INDUSTRIAL CHEMISTRY

Industrial Chemistry

1. Industrial chemistry processes have enabled scientists to develop replacements for natural products

Discuss the issues associated with shrinking world resources with regard to one identified natural product that is not a fossil fuel, identifying the replacement materials used and/or current research in place to find a replacement for the named material

The world’s natural resources are decreasing in supply due to the overwhelming demand from the rapidly increasing world’s population. Through history, natural resources such as wool, cotton were extensively used in the Industrial Revolution. Since then there has been huge demand for other resources such as (e.g. sperm whale oil, ivory, nitrate deposits etc.) for a variety of applications. Thus because these natural resources are running out, there is an increasing need to find replacement materials which can be used in the same applications as its natural counterpart.

Wood is a natural product which is very important and heavily used in society. It is prevalent in our society with applications such as: furniture, paper, bridges and railroad ties, fence posts and electrical poles and textile fabrics. Although wood is a renewable resource, the huge demand for wood by society has exceeded our forests’ ability to supply wood. Adding to the problem is the rapid deforestation happening in countries such as Brazil where areas of trees the size of a football field are being cleared every minute. In the world, there is an average net destruction of 40 million acres of trees. Because of wood’s wide acceptance in many applications, the demand for wood remains high. Therefore alternatives need to be found else we risk losing this natural resource altogether. Some problems of the huge demand for wood:

Deforestation thereby destroying natural habitats and severely affecting organisms. Leads to erosion because when trees are clear-cut, there are neither roots to hold the soil in place nor vegetation to protect soil from hard rain.

Clearance of old growth forests exacerbates climate change problem as this is responsible for 22% of the global carbon dioxide emissions.

Social problems – taking over indigenous lands to obtain wood.

Progress 1: Alternative materials

Construction and building industries account for 25% of the world’s wood harvest. Materials such as steel and concrete have potential to replace wood mainly in building materials. Steel is a metal alloy which contains iron, carbon and other elements including nickel and aluminium. This makes it stronger and more durable than wood thus it can be used to make bridges and other construction works. It also costs less and is easier to erect. Unlike timber, steel is readily available and is one of the strongest construction materials available. Considerable potential also exists for replacing wood with non-fibre alternatives such as straw in paper and Kenaf (an African fibrous plant) in paper manufacture. Disadvantage is that it is expensive.

Progress 2: Replacing old-growth forests with plantations

Now new source of wood where 80% is used for furniture by industry. However disadvantage is that plantations are not beneficial to wildlife and can change the landscape + resource base for local inhabitants. When old-growth forests are destroyed and replaced by plantations, leads to significance rise of CO2 in atmosphere. Thus it’s not really solving problem.

2. Many industrial processes involve manipulation of equilibrium reactions

explain the effect of changing the following factors on identified equilibrium reactions Pressure

Increase in pressure – shift to side with fewer molecules to lessen pressureDecrease in pressure – shift to side with more molecules to raise pressure

Volume Increase in volume = decrease in pressure (shift to more molecules)Decrease in volume = increase in pressure (shift to less molecules)

Concentration Increase in concentration of:

Reactant – shift to product side (to use up excess reactant)Product – shift to reactant side (to use up excess product)

Decrease in concentration of:Reactant – shift to reactant side (to replace reactant)Product – shift to product side (to replace product)

Temperature Exothermic Reaction: (i.e. A + B C + D + Heat)

Increase in temp – shift to left (to reduce heat by using it up)Decrease in temp – shift to right (to replace amount of heat)

Endothermic Reaction: (i.e. A + B + Heat C + D)Increase in temp – shift to right (to use up excess heat)Decrease in temp – shift to left (to replace heat)

interpret the equilibrium constant expression (no units required) from the chemical equation of equilibrium reactionsFrom the following reaction:

aA + bB cC + dDWhere a, b, c, d are the number of moles of substances A, B, C, D

K = [C] c x [D] d [A]a x [B]b

Introduction:Equilibrium

when the rate of the forward reaction is equal to the rate of the reverse reaction concentration of all reactants and products stays constant Macroscopic properties (colour and temperature) remain unchanged Microscopic properties continually change. Involve reversible reactions Can only be achieved in a closed system

Le Chatelier’s Principle:Equilibrium shifts to minimize a change or disturbance imposed on the system

Where [ ] is the concentration of the substances in mol/L

Note: Solids are not to be included in the equilibrium expression. Water (e.g. H2O (l)) or liquids present in large volumes are not to be included in the equilibrium expression.

identify that temperature is the only factor that changes the value of the equilibrium constant (K) for a given equation

Factors that do not change the equilibrium constant (K): Pressure Volume Concentration Catalysts – make the reaction rate faster, equilibrium is reached faster but is not changed

Factors that change the equilibrium constant (K):Temperature

For an exothermic reaction:aA + bB cC + dD + Heat

When the temperature increases – equilibrium shifts left. i.e. [C] and [D] decreases, [A] and [B} increases.

K = [C] c x [D] d

[A]a x [B]b

i.e. the value of K decreases when heat is addedor the value of K increases when heat is removed.

For an endothermic reaction:aA + bB + Heat cC + dD

When the temperature increases – equilibrium shifts to the righti.e. [C] and [D] increases, [A] and [B] decreases

K = [C] c x [D] d [A]a x [B]b

i.e. the value of K increases when heat is addedor the value of K decreases when heat is removed.

identify data, plan and perform a first-hand investigation to model an equilibrium reaction

Real Reaction Analogy of ModelRate of reaction (forward and reverse) Rate of water flow into (forward) and out (reverse) of

plastic containerEquilibrium position (how much products/reactants) Level of water in each containerIncrease in concentration of reactants or products Addition of water in plastic container or reservoir will

result in a new equilibrium that minimises the change.Closed system Closed systemActivation energy for reactants higher than products Different pathways for forward and reverse reactions

Equilibrium:o Rate that pump lifts up the water = rate that water empties out of plastic container.o For a particular pump speed, the levels of water in both containers do not changeo If the pump speed is changed, then a new equilibrium will be reached.

Limitations of Model:o Cannot display the impact of pressure and temperature on equilibrium

choose equipment and perform a first-hand investigation to gather information and qualitatively analyse an equilibrium reaction

We utilised the following equilibrium reaction:

Fe3+ (aq) + SCN-

(aq) FeSCN2+ (aq) + heat

Yellow colourless deep red

Equipment:

o 0.1M iron (III) chlorideo 0.1M ammonium thiocyanateo 0.5M iron (III) chlorideo 0.5M ammonium thiocyanateo 0.5M sodium hydrogen phosphateo Distilled watero 6 test tubeso 100mL beaker

Method:

I. In the beaker, make up a solution by adding 4 drops of 0.1M iron (III) chloride and 4 drops of 0.1M ammonium thiocyanate. Make the total volume up to 50mL by adding distilled water. This is the equilibrium mixture.

II. Divide 30mL of the solution into the 6 test tubes so that there is about the same amount in each.III. Add 3-4 drops of 0.5M iron (III) chloride into test tube 1. Observe any changes. IV. Add 3-4 drops of 0.5M ammonium thiocyanate into test tube 2. Observe any changes. V. Add 0.5M sodium hydrogen phosphate to test tube 3. Observe any changes (phosphate ions react

with Fe3+ ions to produce colourless ions).

VI. Add hot tap water into test tube 4. Observe any changes. VII. Place test tube 5 in an ice bath and observe any changes.

VIII. Keep last test tube as a control to compare any changes. IX. Repeat experiment 10 times for more reliable results.

Explanation of results:

o When drops of 0.5M iron (III) chloride added to equilibrium mixture in test tube 1, solution turned deep red as equilibrium shifts to the right to use up the added iron (III) chloride (Le Chatelier’s principle).

o When drops of 0.5M ammonium thiocyanate added to equilibrium mixture in test tube 2, solution turned deep red as equilibrium shifts to the right to use up the added ammonium thiocyanate (Le Chatelier’s principle).

o When drops of sodium hydrogen phosphate added to equilibrium mixture in test tube 3, solution turned colourless as the phosphate ions react with the Fe3+ ions to produce colourless Fe(PO4)2

2-. o When test tube 4 was heated, solution gradually turned a pale yellow colour as equilibrium shifts

to the left to absorb heat (Le Chatelier’s principle). o When test tube 5 was cooled, solution gradually turned deep red as equilibrium shifts to right to

release heat (Le Chatelier’s principle).

process and present information from secondary sources to calculate K from equilibrium conditions

3. Sulfuric acid is one of the most important industrial chemicals

outline three uses of sulfuric acid in industry

Manufacture of ammonium sulfate fertilizer and phosphate fertilizerSulfuric acid reacts with ammonia produced by a coke oven, to form ammonium sulfate.

2NH3 (g) + H2SO4 (l) (NH4)2SO4 (s)Sulfuric acid converts insoluble calcium phosphate in phosphate rock to mixtures that are soluble in water and are therefore available for plants. This mixture is dried, crushed and used as superphosphate

Dehydrating agentAs a result of its strong water affinity it is used as a drying agent in the production of:

o Chlorine gas - produced by electrolysis of sodium chloride solution.o Explosiveso Detergentso Esters – brings about condensation reactions in the production of esters

Cleaning iron or steelTo galvanise or plate iron or steel, oxides, grease and dirt must be removed. This is done by treating the metal with sulfuric acid.

describe the processes used to extract sulfur from mineral deposits, identifying the properties of sulfur which allow its extraction and analysing potential environmental issues that may be associated with its extraction

Frasch processMethod:

o Three concentric are drilled down into the sulfur deposito Superheated and pressurized liquid water at 160-170 H C/1.5MPa is injected into the sulfur

deposit through the outer pipe. o The high temperature water melts the sulfur. Sulfur-water emulsion formed. o Compressed air is injected through the central pipe and forces the sulphur water to the

surface through the middle pipe. o The emulsion is collected at the surfaceo As it cools, the emulsion separates into water and solid sulfur

Properties of sulfur related to its extractiono Very low melting point (113 H C) due to weak dispersion forces between molecules, allowing

the superheated water to melt the sulfur at 160 H Co Insoluble in water and does not react chemically with it. Its insolubility allows it to be

separated from the water at the end of the Frasch processo Low density produces a sulfur-water emulsion that is light and readily transported to the

surface by air pressure.o Inert, non-toxic and non-volatiles, which poses no health risks to on-site workers.

Potential environmental issueso Recovered water contains dissolved minerals. Needs to be sufficiently cooled before to

avoid thermal pollution and must be recycled to avoid contamination of local ecosystemo While sulfur is non-volatile and does not escape into the environment, it can be oxidized

very easily to form the pollutant sulfur dioxide. Hence, the extracted sulfur must be cooled quickly to avoid this from happening.

o Underground caverns left by the extraction of sulfur can result in ground subsidences as a result of the difficulty to back-fill the mine.

Extraction from natural gas and crude oilSulfur can also be obtained from natural gas and crude oil. Incomplete combustion of H2S produces elemental sulfur:

3H2S (g) + O2 (g) → 2H2O (g) + 3S (g) + SO2 (g)

outline the steps and conditions necessary for the industrial production of H2SO4 from its raw

materials

Contact Process

1. Elemental sulfur is combusted in excess, dry oxygen to ensure complete combustion. S (s) + O2 (g) → SO2 (g)

2. Sulfur dioxide is passed over vanadium pentoxide or platinum catalyst at 400 H C to produce sulfur trioxide which takes place in a catalytic converter.

2SO2 (g) + O2 (g) → 2SO3 (g) [ΔH = –99 kJ/mol]

3. The cooled sulfur trioxide is then dissolved in sulfuric acid in the absorption tower to produce oleum (H2S2O7)

SO3 (g) + H2SO4 (l) → H2SO4 (l) 4. The oleum reacted with water in the diluter, forming 98% sulphuric acid.

H2S2O7 (l) + H2O (l) → 2H2SO4 (l)

Note: Gaseous sulfur trioxide cannot be added directly to water as the reaction is very exothermic and would produce a dangerous sulfur dioxide mist. To avoid this problem, sulfur trioxide is added to sulfur dioxide to form liquid before dissolving in water to produce sulfur dioxide.

describe the reaction conditions necessary for the production of SO2 and SO3

Combustion of Sulfuro sulfur must be cleaned with dry oxygeno high surface area (i.e. crushed rock) – high yieldo high temperature (1000 H C) – high rate of reaction

Catalytic ConverterIt is an equilibrium reaction which involves a compromise between reaction rate, equilibrium yield and economic factors.

o Temperatures from 450 – 600 H C will produce a fast rate of reaction and good yield at an appropriate economic cost.

At room temperature, the yield would be extremely high, though it will occur at an uneconomically slow rate.

Increasing the temperature increases the rate of reaction; however, the forward reaction is exothermic, so increasing the temperature pushes equilibrium to the left to absorb the heat, thus decreasing the yield.

Furthermore, a high temperature could damage the catalyst, making it less efficiento Catalyst, vanadium oxide is used to increase the rate of reaction and minimise economic

cost of productiono Increasing the pressure would push equilibrium to the right, to reduce the number of

particles and thus pressure. This would produce a higher yield.o Excess oxygen is also used to push equilibrium to the right to increase the yield.

All these reaction conditions produce a yield of 99% sulfur trioxide.

apply the relationship between rates of reaction and equilibrium conditions to the production of SO2 and SO3

Conditions + reaction rate Increase yield Economic factors Conditions used

Temperature High temperature

e.g. 1000 H C

Low temperature

e.g. 25 H C

High temperatures involve a

large use of electricity

which is expensive

Medium

temperature e.g.

450 – 600 H C

Pressure Between 100 and

200 kPa increase

collision

frequency of

reacting gases

High pressure

drives

equilibrium to the

right, reducing

no. of particles.

High-pressure apparatus is

extremely expensive.

Low pressure of

100 to 200 kPa

Concentration

of reactants --------------------Increase conc. of

reactants

Increasing the amount of

oxygen will have minimal if

no economic cost

Excess oxygen

used in converter

Other Catalyst Removal of

product – drives

equilibrium to the

right

---------------------------Removal of sulfur

trioxide to increase

yield. Use of

catalyst.

describe, using examples, the reactions of sulfuric acid acting as:

Oxidising Agento Reactive metals are oxidised by dilute sulfuric acid, releasing hydrogen gas.

Zn (s) + 2H3O+ → Zn2+ (aq) + H2 (g) + 2H2O (l)In concentrated sulfuric acid reactions, it is the sulfate ion that is the oxidant. The sulphate ion is usually reduced to sulfur dioxide, sulfur or hydrogen sulphide.

o Oxidation of bromide and iodide ions to the elements bromine and iodine, while sulfuric acid is reduced to sulfur dioxide. Smell gases. Brown vapour produced for bromine.

2KBr (s) + 3H2SO4 (l) → 2KHSO4 (s) + SO2 (g) + 2H2O (l) + Br2 (l)2KI (s) + 3H2O (l) 2KHSO4 (s) + SO2 (g) + 2H2O (l) + I2 (s)

o Oxidation of unreactive metals such as copper, mercury, tin and lead to produce metal sulfate, sulfur dioxide and water. Sizzling, gas formed.

Cu (s) + 2H2SO4 (aq) → CuSO4 (aq) + 2H2O (l) + SO2 (g)Sn (s) + 2H2SO4 (aq) → SnSO4 (aq) + 2H2O (l) + SO2 (g)

Dehydrating Agento Conc. sulfuric acid removes water form carbohydrates and other organic substances –

leaving black carbon to rise out of the beaker.C12H22O11 + 11H2SO4 (aq) → 12C (s) + 11H2O (l)Sucrose

o Removes water from hydrated copper sulfate crystals turning the blue crystals in to the white crystals

CuSO4.5H2O → CuSO4 (s) + 5H2O (l)o Dehydrates ethanol to produce ethylene.o Catalyst used in the manufacture of esters to remove water and thus drive equilibrium to the

right, increasing the yield. describe and explain the exothermic nature of sulfuric acid ionisation

The ionisation of sulfuric acid is extremely exothermic, releasing a large amount of heat. Sulfuric acid ionises in two exothermic steps:

H2SO4 (aq) + H2O (l) → H3O+ (aq) + HSO4- (aq) + HEAT

HSO4- (aq) + H2O (l) → H3O+ + SO4

2- (aq) + HEAT

identify and describe safety precautions that must be taken when using and diluting concentrated sulfuric acidTo protect your skin and clothing

o Always wear protective gloves and a laboratory coat as conc. sulfuric acid will char skin and cotton.

o Always wear safety glasses.o If sulfuric acid contacts the skin, it must be washed off with large amounts of running water.

If larger amounts are spilled on the skin, it is best to wipe the excess away rapidly with a paper towel and then wash with large volumes of water.

When diluting sulfuric acid:o Add small amount of acid to large volumes of water, stirring continuously to disperse the

heat.If sulfuric acid is spilt on the bench or floor:

o It should be isolated quickly to prevent spreading. o Sand should be spread over the acid to absorb it. o Place the acid soaked sand in plastic buckets for disposal and neutralisation with sodium

bicarbonate. o The floor should then be cleaned with sodium bicarbonate then water and detergent.

When storing conc. sulfuric acid:o Use well sealed containers, stored in a secure, cool and well ventilated room in small plastic

trays to prevent that any leaks do not contact the wooden workbench or shelf.o Store away from metals, bases and water as sulfuric acid will react with these substances

exothermicallyWhen transporting sulfuric acid:

o Stored in steel drums and tankers as steel is stronger than glass or plastic and is less likely to rupture if there is an accident.

o The acid will not react with the metal as an inert oxide layer will form between the acid and the metal.

o Water must not be allowed to contaminate the conc. sulfuric acid as it will result in significant ionisation and a build up of heat. It will also react with the steel to produce hydrogen gas.

gather, process and present information from secondary sources to describe the steps and chemistry involved in the industrial production of H2SO4 and use available evidence to analyse the process to predict ways in which the output of sulfuric acid can be maximised

The first step in the process is the formation of sulfur dioxide. Molten sulfur (extracted using the Frasch process) is sprayed into a combustion furnace where it reacts with dry air which mainly consists of oxygen. The air is dried by passing it through concentrated sulfuric acid which acts as a dehydrating agent by absorbing the moisture. The air is dried to prevent SO2 reacting with water to form unwanted sulfurous acid. It is an exothermic reaction which essentially goes to completion:

S (l) + O2 (g) SO2 (g) + heat

The second step in the process is the production of sulfur trioxide. The sulfur dioxide produced from the previous step is entered into a conversion tower where it is reacted with excess oxygen. In the conversion tower there are the following reaction conditions to maintain a balance between yield of sulfur trioxide and the rate of reaction:

Moderate temperatures of around 400-550ºC. Pressures of around 1-2 atm pressure. Vanadium (V) oxide catalyst – V2O5 which are situated on silica pellets to increase surface area for the reaction.

In this step, the reactant gases pass over the first catalyst bed at a temperature of around 550ºC which causes the conversion of around 70% sulfur trioxide. To increase the yield, the temperature is decreased to 400ºC at the above catalyst bed which results in the formation of more sulfur trioxide as the reaction is exothermic; decreasing temp will shift equilibrium to the right. Finally the gas is cooled again to produce 99.7% conversion rate of sulfur trioxide. Reaction is below:

2SO2 (g) + O2 (g) 2SO3 (g) + heat

The 3rd step in the contact process is the production of oleum. The sulfur trioxide produced in the last step is reacted with concentrated sulfuric acid which is recycled from the last step in the process. The reaction occurs in an absorption tower:

SO3 (g) + H2SO4 (l) H2S2O7 (l)

This reaction is utilised instead of reacting sulfur trioxide with water to produce sulfuric acid. This is because if sulfur trioxide is reacted with water to form sulfuric acid, the solution would react explosively and lots of heat would be generated as it is exothermic. A mist of sulfuric acid droplets would form and it would be expensive for industry to separate this mist from the air.

Finally the last step in the process is the production of concentrated sulfuric acid. The oleum produced in the previous step is diluted in water to form 98% concentrated sulfuric acid. Some of the concentrated sulfuric acid is recycled to react with SO3 to produce oleum and the rest of it is collected and stored in a storage tank.

H2S2O7 (l) + H2O (l) 2H2SO4 (l)

Output of sulfuric acid can be maximised by:

o Adding excess oxygen into the combustion furnace. o Moderate – low temperatures in the conversion tower to increase yield of sulfur trioxide. o Add excess oxygen to the sulfur dioxide in the conversion tower. o Constant removal of sulfur trioxide in the conversion tower.

perform first-hand investigations to observe the reactions of sulfuric acid acting as:– an oxidising agent– a dehydrating agent

An oxidising agentPotassium bromide + H2SO4H2SO4 used as oxidising agent – bromine ions become bromine atoms

2Br- Br2

2KBr(s) + 3H2SO4(l)   2KHSO4(s) + Br2(g) + SO2(g) + 2H2O(l)Observation: red/orange vapour/gas forms

A dehydrating agent1. Place sugar in beaker (white, crystalline solid)2. Add concentrated sulfuric acidObservation: Solution gradually got darker, steam was released, black column of carbon rose out of beaker C12H22O11(s) 12C(s) + 11H2O(l) (conc H2SO4 above arrow)

use available evidence to relate the properties of sulfuric acid to safety precautions necessary for its transport and storage

Since sulfuric acid is one of the most important industrially produced chemicals and yet it is so corrosive and harmful means that safely transporting sulfuric acid is essential.

Concentrated sulfuric acid

Concentrated sulfuric acid contains mostly molecules thus there are no free ions. This means that it can be transported in steel or iron containers as it does not contain H+ ions to react with the iron/steel. In addition to this, iron/steel containers are robust and strong thus it is ideal to transport concentrated sulfuric acid. Care must be taken to prevent any moisture from entering container as the concentrated sulfuric acid can absorb the moisture and ionise rapidly producing excessive amounts of heat (exothermic reaction).

Dilute sulfuric acid

However dilute sulfuric acid (H2SO4.H2O) contains hydrogen ions (because it’s fully ionised) which can react with the steel/iron containers. Thus glass or plastic containers are used to store or transport dilute sulfuric acid as the hydrogen ions do not attack these containers

4. The industrial production of sodium hydroxide requires the use of electrolysis

explain the difference between galvanic cells and electrolytic cells in terms of energy requirementsCell feature Galvanic Cell Electrolytic CellOxidation Anode (–) Anode (+)Reduction Cathode (+) Cathode (–)Electron flow Anode to cathode From neg terminal to cathode

and from anode to positive terminal

Net cell reaction Spontaneous Non-spontaneousElectrical energy Produced Required Feature Galvanic Cell Electrolytic CellUses In batteries To electroplate metals as well

as purifying metals. Diagram

outline the steps in the industrial production of sodium hydroxide from sodium chloride solution and describe the reaction in terms of net ionic and full formulae equations

First of all, salt water is collected from the oceans. However various impurities are present in salt water. Thus salt water needs to be purified and the contaminants removed. Here are some equations showing the removal of these impurities in salt water:

Contaminant Removal from sea waterCalcium ions Calcium ions are removed from salt water by reacting

it with sodium carbonate: CaCl2 (aq) + Na2CO3 (aq) CaCO3 (s) + 2NaCl (aq)_

Magnesium ions Magnesium ions are removed from salt water by reacting it with sodium hydroxide: Mg(NO3)2 (aq) + 2NaOH (aq) Mg(OH)2 (s) + 2NaNO3

(aq)

Iron ions Iron ions are removed from salt water by reacting it with sodium carbonate or sodium hydroxide: Fe(NO3)2 (aq) + Na2CO3 (aq) FeCO3 (s) + 2NaNO3 (aq)

Fe(NO3)2 (aq) + 2NaOH (aq) Fe(OH)2 (s) + 2NaNO3 (aq)

Sulfate ions Sulfate ions are removed from salt water by reacting it with calcium chloride: K2SO4 (aq) + CaCl2 (aq) 2KCl (aq) + CaSO4 (s)

After the removal of these impurities, the salt water (sodium chloride + water) is concentrated. This can be referred to as saturated brine. Then this brine undergoes electrolysis to produce:

o Sodium hydroxideo Hydrogen gaso Chlorine gas

FORMULA EQUATION:

2NaCl (aq) + 2H2O (l) 2NaOH (aq) + H2 (g) + Cl2 (g)

FULL IONIC EQUATION:

2Cl- (aq) + 2H2O (l) 2OH-

(aq) + H2 (g) + Cl2 (g) (After cancelling Na+ spectator ion)Looking at the above reactions, the chlorine ions in the salt water solution are oxidised to form chlorine gas and the water in the salt water solution is reduced to form hydroxide ions and hydrogen gas. Electrons are lost from chlorine ions and these electrons are gained by the water molecules.

distinguish between the three electrolysis methods used to extract sodium hydroxide: mercury process diaphragm process membrane process

by describing each process and analysing the technical and environmental difficulties involved in each process

MERCURY CELL

o Titanium plates are used as anodeso Chloride ions are oxidised at the anodes to produce chlorine gas which is removed from the

cell and stored in cylinderso Deplete brine is removed from the system and contains small amounts of mercury.o Mercury acts as a liquid cathode at the bottom of the container and reduces sodium ions form

a mercury-sodium amalgam.o The amalgam into the decomposer which contains pure water.o The water reacts readily with the sodium ions in the amalgam to produce sodium hydroxide

and hydrogen gas. Hydrogen gas is collected and stored in cylinders. o The remaining mercury is recycled back into the system.

Environmental concernso Although theoretically, the mercury is recycled infinitely throughout the system, some

mercury is inevitably discharged from cell and into the ocean through the deplete brine. o Some bacteria in the ocean can convert mercury into compounds such as dimethyl mercury,

Hg(CH3)2, which will be passed through the food chain to humans. Mercury poisoning affects the nervous system and can cause brain damage.

DIAPHRAGM CELL

o Consists of two components separated by an asbestos diaphragm to allow a flow of sodium ions

o Titanium anode and iron mesh cathode.o Chloride ions are oxidised at the anode to produce chlorine gaso Water is reduced at the cathode producing hydrogen gas.o Sodium ions flow from the anode through the diaphragm to the cathode to balance the charge

of the hydroxide ion formed there.o Sodium ions react with hydroxide ions to form sodium hydroxide.

Technical and Environmental difficulties:o Keeping hydrogen and chlorine gas separated as they react vigorously on contact)o Minimising contact between hydroxide ion and chorine in solution because OH– + Cl2 forms

bleach ClO– in the depleted brine solution which is deposited in the ocean. o Thus, a slight positive pressure is maintained on the anode side of the diaphragm, to minimise

the diffusion of hydroxide ions to the anode side.o However, the slight positive pressure results in the diffusion of chloride ions to the cathode

compartment resulting in impure sodium hydroxide that contains chlorine.o The diaphragm is made of asbestos and small losses do occur at great risk to human health

MEMBRANE CELL

o The set-up is almost exactly like the diaphragm cell, except the membrane separating the anode compartment and the cathode compartments is an ion-exchange membrane interlaced with inert negative ions which allow sodium ions to move the cathode compartment

o Chlorine and hydroxide ions, thus, cannot pass through the membrane as they are repelled by it.o In this cell, the conc. sodium hydroxide produced is pure and does not contain chlorineo Depleted brine solution does not contain hypochlorite, ClO-

Mercury Cell Diaphragm Cell Membrane CellElectrolyte Conc. brine (NaCl) solutionCathode Liquid mercury Iron mesh Iron meshAnode Titanium Titanium TitaniumCathode reaction Na+ + e– → Na(Hg)

2Na + 2H2O → 2NaOH + H2

2H2O (l) + 2e– → H2 (g) + 2OH– (aq)

Anode reaction 2Cl– (aq) → Cl2 (g) + 2e–

Overall reaction 2NaCl (aq) + 2H2O (l) → Cl2 (g) + H2 (g) + NaOH (aq)Diaphragm ---------------------------- Asbestos Ion exchange membraneExpense to operate Expensive Expensive More expensive - new

technology Conc NaOH made Highest (~50%) Lowest (~11%) Medium (30-40%)NaOH produced with brine or in a separate chamber?

Brine and NaOH mix and have to be separated.

Separate chambers Membrane will not let OH- or Cl- ions through

thus in separate chamber.

Electrical energy Operating voltage 4-4.5 volts. Operating voltage 4-5 volts.

Operating voltage 3-4 volts and may become

lower.Environmental/health problems

Mercury is a heavy metal and is toxic. It bioaccumulates in the food chain and can damage kidneys in humans.

Asbestos is toxic and may causes diseases

such as asbestosis and mesothelioma

No asbestos or mercury thus having no

environmental/health problems.

identify, plan and perform a first-hand investigation to identify the products of the electrolysis of an aqueous solution of sodium chloride

Basically different products can be formed when conducting electrolysis of sodium chloride. The products formed depend on the concentration of the sodium chloride. If dilute NaCl is used, usually oxygen gas would be produced at the anode and hydrogen gas + hydroxide ions produced at the cathode. However if concentrated sodium chloride is used, chlorine gas would be produced at the anode and hydrogen gas + hydroxide ions produced at the cathode.

To identify the substances at each electrode, glowing splint test can be used to identify gas and litmus paper or universal indicator can be used to identify solution. If in the glowing splint test a ‘popping’ noise is heard, then the gas is hydrogen. If the splint reignites, then it is oxygen. If litmus paper is bleached, solution contains chloride ions and if solution turns universal indicator purple then there are hydroxide ions present.

Safety includes wearing safety goggles to prevent corrosive sodium hydroxide from splashing into eyes causing burns and irritations. Experiment should be undertaken in a fume cupboard because chlorine gas is toxic and can cause respiratory problems and is corrosive.

analyse information from secondary sources to predict and explain the different products of the electrolysis of aqueous and molten sodium chloride

In the electrolysis of sodium chloride there are two possibilities at the anode:o H2O → 2e– + ½O2 + 2H+ [emf = –1.23V]o Cl– → e– + ½Cl2 [emf = –1.40V]

Possibilities at the cathode:o Na+ + e – → Na [emf = –2.71V]o H2O + e– → ½H2 + OH– [emf = –0.83V]

Aqueous NaCl (dilute)Anode: H2O → 2e– + ½O2 + 2H+ [as the emf is lower – less energy needed for the reaction to occur]Cathode: H2O + e– → ½H2 + OH– [as emf is lower]

Molten NaCl (conc.)Anode: Cl– → e– + ½Cl2 As [Cl–] increases, the emf for the second anode reaction decreases to approximately –1.10V, making the reaction easier to occur.

Cathode: H2O + e– → ½H2 + OH–

In the electrolysis of molten sodium chloride, there are only sodium and chloride ions present. Thus at the anode the only possible reaction is when the chlorine ions oxidise to form chlorine gas:

2Cl- (l) Cl2 (g) + 2e-

The only possible reaction at the cathode is when the sodium ions are reduced to form sodium metal:

2Na+ (l) + 2e- 2Na (l)

FULL EQUATION: 2NaCl (l) Cl2 (g) + 2Na (s)

Thus from the electrolysis of molten sodium chloride it is easy to predict the products formed. The products formed are: chlorine gas and sodium metal.

However the electrolysis of aqueous sodium chloride is more complicated due to the presence of water. The possible anode reactions are: when chloride ions are oxidised to form chlorine gas OR when water molecules are oxidised to form hydrogen ions + oxygen gas.

If at anode chlorine ions oxidise to form chlorine gas: 2Cl- (l) Cl2 (g) + 2e-

If at anode water molecules are oxidised: 2H2O (l) O2 (g) + 4H+ (aq) + 4e-

However the electromotive force (EMF) for each reaction is different. The reaction with the highest EMF will most likely proceed (more spontaneous reaction). The E value (using data sheet) for 1st reaction is -1.36V and 2nd reaction is -1.23V. Theoretically, oxygen would be expected to form at the anode. However this is not the case. Oxygen is only produced with very dilute NaCl solutions. With concentrated NaCl solutions chlorine gas is produced instead. This occurs because of an effect called over voltage and also because the conditions are different to those in which standard reduction potentials are measured e.g. concentrations of Cl- ions is high, not 1 molL-1.

The possible reactions at the cathode are when sodium ions are reduced to form sodium ions OR when the water molecules are reduced to form hydroxide ions and hydrogen gas.

If at cathode sodium ions are reduced: Na+ (aq) + e- Na (s)

If at cathode water molecules are reduced: 2H2O (l) + 2e- 2OH-

(aq) + H2 (g)

However like at the anode, the electromotive force (EMF) for each reaction is different. The reaction with the highest EMF will most likely proceed (more spontaneous reaction). The E value (using data sheet) for 1st reaction is -2.71V and 2nd reaction is -0.83V. Thus the 2nd reaction will occur at the cathode since it has a higher E value meaning it is a more spontaneous reaction.

Thus in most cases the products formed are: chlorine gas and hydrogen gas + hydroxide ions.

5. Saponification is an important organic industrial process

describe saponification as the conversion in basic solution of fats and oils to glycerol and salts of fatty acids

Ester + Sodium Hydroxide → Alkanol + Sodium salt of alkanoic acidOR more prescisely:

Ester + Hydroxide ion → Alcohol + carboxylate anionTriglyceride + sodium hydroxide → soap + glycerol(fats and oils)

Fats and oils are esters of glycerol (1, 2, 3 – trihydroxy – propane.) Acids added to glycerol in esterification may be:

o saturated – contain only single bonds in the carbon chain (solid fats)o unsaturated – contain some double or triple bonds in the carbon chain (liquid oild)

Animal fats and vegetable oils are esters known as triglycerides.

Animal fats:o Saturated palmitate group CH2OOC(CH2)14CH3 o Saturated stearate group CHOOC (CH2)16CH3

Vegetable fats:o Unsaturated oleate group CH2OOC(CH2)7 == CH(CH2)7CH3

Example of saponification:Glyceryl tristearate + Sodium hydroxide → Sodium stearate + glycerol

(soap)

describe the conditions under which saponification can be performed in the school laboratory and compare these with industrial preparation of soap

Basically in a school laboratory, we are limited in resources thus what we did was obtain coconut oil (as the oil) because it’s cheap and readily available and added sodium hydroxide to it and boiled the solution. With constant stirring, we added 2-3 drops of food colouring. After about 10 minutes, we added sodium chloride to precipitate out the soap and we allowed it to cool. Then we left it to dry and the next day we extracted soap and tested it further. However In the industrial production of soap, there are many factors which differ from the school laboratory production of soap.

Industrial production method of soap:

Fatty Acid Neutralisation process:

Initially, the fats and oils are hydrolysed by high pressure steam. This breaks down the fats into fatty acids and glycerol.

At this point, glycerol is drawn away, purified and sold to the cosmetics industry for use in creams etc. The fatty acids are passed into another vessel where they are distilled. This causes the separation of

different fatty acids from each other. At this point, some fatty acids can be drawn off and sold as individual substances. This also allows the control of the range of fatty acids (different chain lengths) which are present in a particular soap.

The fatty acids continue into the next reaction vessel where they are mixed with an alkali (usually sodium hydroxide) and neutralised to form soap in a continuous process.

The soap is recovered and is then pumped into giant mixers called crutchers where other desired ingredients are added to it e.g. colours, fragrances.

Finally the soap is rolled into flakes, cast into bars or spray-dried into soap powder. Now it is ready for commercial use.

In the batch process, the raw materials are mixed together in a vessel and allowed to react together. After the reaction, the desired products are separated from reaction mixture.

In the continuous process, the raw materials are fed in at one end of the industrial plant (or at various stages along the way) and the products are withdrawn at the other end in a continuous flow.

Another prominent industrial production of soap is the kettle boiled batch process. In this method, large amounts of fats/oils, caustic soda (sodium hydroxide) and water are added to a large open steel tank called a kettle. High pressures and temperatures are used to keep the reaction boiling. It also keeps the reaction well stirred. At the conclusion of the saponification reaction, additional salt is added to the mixture to solidify the soap and it’s washed with steam to separate glycerol.

PRODUCING SOAP IN SCHOOL LAB vs . INDUSTRIAL PRODUCTION OF SOAP

Factor School laboratory process Industrial processRaw materials Coconut oil, sodium

hydroxide, water. These are often pure.

Mixture of blended fats and oils with sodium hydroxide. Some common fats and oils include: tallow, coconut oil, palm kernel oil and palm oil. However these reactants are not pure – wastes e.g. tallow from discarded beef from abattoir. Blended in exact stoichiometric amounts.

Mixing raw materials

All added at the start. Continuously stirred solution with a stirring rod.

Kettle process: All added at the startNeutralisation process: fats/oils hydrolysed by steam and then fatty acids are neutralised. The materials are stirred by using steam or electricity.

Temperature and pressure

Standard atmospheric pressure. Temperature about 50-80ºC using Bunsen burner.

Higher temperature and pressures. Usually temperatures between 240-270ºC and pressures of about 4.5-5 MPa.

Container 250mL beaker Kettle process: A large open steel tank called a kettle. Neutralisation process: reacted in large vessels

and then perfumes, colours added in huge tank called a crutcher.

Time Reaction in about 1 hour and we left it overnight to solidify soap.

Washing and setting of soap takes several days.

Disposal of wastes

Decanted liquid layer above soap (mainly glycerol + water + excess NaOH)

In both processes, glycerol is removed, purified and sold to the cosmetics industry for use in creams. However in neutralisation process some fatty acids are removed and sold individually.

Further processing

We added food colouring to the soap.

Soap washed with steam, colour dyes and fragrances added, distilled to remove impurities and vacuum dried. Then soap cast or stamped into bars, rolled into flakes or spray dried into powder.

Catalyst Nil Kettle process: metal catalystNeutralisation process: zinc oxide

Safety Wear safety goggles and continuously stir.

Safety goggles, protective clothing e.g. coats.

account for the cleaning action of soap by describing its structure

Structure of soap:

Composed of positive ion (usually sodium or potassium) and negative ion Negative ion made up of carboxylate end group, called the head and a long hydrocarbon chain

called the tail The head is hydrophilic while the tail is hydrophobic The tail dissolves in dirt while the head forms a bond with water, causing micelles to form When soap dissolves in water, the cation separates from the carboxylate anions. Soap interferes with normal hydrogen bonding in the water resulting in a lower surface tension.

First of all, soap is a surfactant meaning that when it enters the water, it decreases the surface tension of the water. This is because soap contains the long hydrocarbon tail which disrupts the hydrogen bonding between water molecules thus decreasing the surface tension. Soap has an effective cleaning action because of its structure.

The first step in soap’s cleaning action is shown in the following diagram:

This diagram shows when the soap molecules enter the water. Notice that the positive ion in soap molecule dissociates in the water and hence does not

take part in the cleaning action of soap.

In the diagram above, we can see that the oil droplet has been surrounded by the soap molecules. The long hydrocarbon tails are embedded in the oil molecule because it’s non polar and so is the oil droplet thus they interact using dispersion forces. They repel the water molecules as they are hydrophobic (water hating). However the negative anion sticks out because it is attracted to the water molecules at it is charged and polar. The anion forms hydrogen bonds with the water molecules and thus is hydrophilic (water loving).

In the diagram above, the interaction between the long hydrocarbon tails with the oil droplet and the anion with the water molecules are strong enough to lift the oil droplet from fabric and thus leave oil droplet suspended in the water. Note that the soap molecules are able to break up the oil/dirt forming smaller droplets called micelles. Now the oil droplet is ready to be removed.

explain that soap, water and oil together form an emulsion with the soap acting as an emulsifierEmulsion – when two immiscible liquids are dispersed through each other using a surfactant

do not settle on standing cannot be separated by filtration

Oil-in-water emulsion:

The oil molecules are surrounded by water thus the hydrophobic hydrocarbon tails are attracted to the oil droplet (dispersion forces) and the charged anion head is attracted to the water molecules (hydrogen bonds). The oil micelles do not clump together because the anionic heads of adjacent soap molecules repel each other (electrostatic attraction). Thus the soap acts as an emulsifier as it allows the oil droplets to remain suspended in the water without forming a layer on top.

Water-in-oil emulsion:the water molecules are surrounded by oil thus the hydrophobic hydrocarbon tails are attracted to the surrounding oil (dispersion forces) and the charged anion head is attracted to the water molecules (hydrogen bonds). The soap acts as an emulsifier as it allows the water droplets to remain suspended in the oil without forming a layer

distinguish between soaps and synthetic detergents in terms of:

Hard water is the name given to water which has excessive amounts of calcium and magnesium ions.

Factor Soap DetergentStructure Three types of detergent:

anionic, cationic and non-ionic. These structures are shown in the next dot point. Usually has polar head like soap + hydrocarbon tail.

Chemical composition

Sodium or potassium salts combined with fatty acids from triglycerides.

Usually hydrocarbons with a sulfate, sulfonate or another hydrophilic group at the end.

Effect in hard water Soap forms a greyish precipitate called scum due to the reaction between the soap anions and the calcium + magnesium ions in the water. Thus this reduces cleaning ability of soap and reduces lathering.

Lathers in hard water and does not form a precipitate with calcium or magnesium ions.

distinguish between anionic, cationic and non-ionic synthetic detergents in terms of:

Chemical compositionANIONICLong hydrocarbon tail and an anionic head, which is usually a sulfonate, i.e. R – O – SO2 – O–

Strongly lathering, more effective surfactant than soap

CATIONICo Derivatives of the ammonium ion in which the H atoms are replaced by alkyl groupso Generally there are 1 or 2 long chain alkyl groups (10 to 20 C atoms) and 2 or 3 methyl groups.o Strongly lathering, binds strongly to negative surfaces of wet fabric, hydrocarbon tails reduce

fibre tangling, excellent for cleaning plastic products, mild antiseptic properties.Example: Cetyl trimethyl ammonium bromide

NON-IONICo Have a long hydrocarbon tailo The polar head is made by joining several ethoxy groups (– CH2 – CH2 – O –) together with an H

on the endo Weakly lathering- important to prevent foam clogging of water jets in dishwashers, strong alkalis

present to dissolve the grease.Example: Dodecyl alcohol ethoxyalate

(– CH2 – (CH2)8 – CH2 – CH2 – CH2 – O – (CH2 – CH2 – O)n – CH2 – CH2 – OH

ANIONIC CATIONIC NON-IONICo laundry detergentso cleaning glasso hand soapso shampooso dishwashing liquid

o fabric softenerso hair conditionerso clean plastico mild antiseptics

o paintso cosmeticso adhesiveso mixed with anionic and

cationic detergents to reduce

o heavy-duty engine lubricant amount of lather or foam

perform a first-hand investigation to carry out saponification and test the product

Method for Saponification: NaOH + H2O + C2H5OH boiled with coconut oil in a large beaker with a magnetic stirrer and

boiling chips Pour water into beaker when foam rises too high Wait for it too cool down substantially before adding NaCl Soap is “salted out” with NaCl solution as NaCl ions dissolve more readily into water, thus soap

forms. Wash soap of NaOH

Method for testing product:1. Set up 3 test tubes each with the same amount of distilled water2. Add equal amounts (1 spatula) of one emulsifier to each test tube3. Shake for one minute4. Measure depth of bubbles with a ruler5. Repeat steps 1, 2 and 3 with hard water6. Repeat steps 1 and 2 with a mixture of oil and water (use a control)

Results:Lab Soap Commercial Soap Detergent

Distilled water 2 cm 3.5 cm 4.5 cmHard water No bubbles (precipitate formed) 2.5 cmOil and Water Forms an emulsion

Controlled variables – amount of emulsifier- Amount of solvent- Time shaken

gather, process and present information from secondary sources to identify a range of fats and oils used for soap-making

Tallow - fat obtained as a by product of beef (and sometimes sheep) processing and is the most common sort of animal fat used in soap manufacture. It is usually obtained from the wastes discarded in abattoirs.

Coconut Oil - from the dried fruit of the coconut palm tree. The fruit is dried and the oil is pressed out of the dried fruit.

Palm kernel oil - from the nuts of the palm tree and has similar properties to coconut oil. Palm oil - from the fleshy fruit of the palm trees rather than the nut. Palm oil has longer chains than

palm kernel oil. This gives it properties similar to tallow.

perform a first-hand investigation to gather information and describe the properties of a named emulsion and relate these properties to its uses

Mayonnaise: Mayonnaise is an emulsion of vegetable oil and egg yolks, with the emulsifier being the lecithin

found naturally in the egg yolk. It’s a vinegar and oil emulsion where lecithin stabilises the mixture.

Properties in Relation to Uses: Mayonnaise is a stable emulsion, due to the strong emulsifying properties of lecithin. It does not

separate into its component liquids even when stored for long periods of time. This property is useful as it is a food product; it needs to stay in an edible condition, in

storage, for relatively long periods of time. Mayonnaise also has the property of having a creamy feel, and not feeling oily thus having a

pleasant taste. Because of the emulsifier, mayonnaise can be used in sandwiches as it is easily spread.

perform a first-hand investigation to demonstrate the effect of soap as an emulsifier

Aim: To demonstrate the effect of soap as an emulsifier. Method:

1. Obtain a large conical flask2. Add about 50mL of distilled water to flask. 3. Add about 50mL of vegetable oil to flask, shake and observe what occurs. 4. Obtain second conical flask and add about 50mL distilled water. 5. Add about 50mL of vegetable oil into the flask.6. Add 4-5 drops of liquid soap/detergent or a few flakes of solid soap. 7. Shake and observe what happens.

Results/observations: Water + oil emulsion Soap Added

Conclusion:

When soap was added to the water + oil emulsion, a cloudy layer was observed between the water and oil layers. We also observed tiny oil droplets suspended in the soapy water thus demonstrating soap’s effectiveness as an emulsifier.

solve problems and use available evidence to discuss, using examples, the environmental impacts of the use of soaps and detergentsBiodegrability

early anionic detergents were not biodegradable so foams persisted in waterways for years This was because of the highly branched hydrocarbon tails that microbes in the environment

found hard to decompose This environmental problem was solved by creating synthetic detergents with non-branching

tails which were biodegradable and could be broken down readily by microbial decomposers.

Phosphates Although synthetic detergent was more successful in hard water, the presence of calcium

and magnesium ions still resulted in the flocculation small colloidal particles, such as clay, which would soil clothes.

To prevent this, phosphates or ‘builders’ were added to detergents However, the presence of phosphates resulted in algal blooms in natural bodies of water as

well as eutrophication of the waterways Recently, sodium zeolate has replaced phosphates. They help remove calcium and

magnesium ions from hard water by exchanging sodium ions for calcium and magnesium ions.

Soaps have little impact on the environment because they are made from natural organic products which are easily broken down by bacteria thus they are biodegradable. They are broken down into simpler substances such as water and carbon dioxide.

However detergents have significant impacts on the environment. Earlier detergents contained branched hydrocarbon chains thus it was harder for bacteria to break down – resulting in less biodegradability. When these detergents entered waterways, they caused excessive foaming resulting in aesthetical and environmental problems. To fix this problem of excess foaming and depletion in biodegradability, the structure of detergents have changed with new detergents having linear chains which are much more easily broken down by bacteria thus increasing its biodegradability. However the disadvantage with these new detergents is that they contain phosphate builders (e.g. sodium tripolyphosphate – Na5P3O10). These builders are added to enhance the cleaning power of the detergent by increasing the alkalinity and to help ‘soften’ the water. However when these detergents are disposed in waterways, there are high levels of phosphates present. Phosphates are nutrients for vegetation but it high levels in waterways leads to excessive growth of algae.

This is a huge problem as the algae form a layer on the top of the water, thereby starving the plants and organisms below essential sunlight. They also use up oxygen in the water and hence there are depleting levels of oxygen in the water, affecting plants and aquatic organisms such as fish, crab. When this algae die, they use up more oxygen in the water as they decompose. Thus eutrophication occurs as a result from the release of these detergents from households and industries.

To combat the problem of eutrophication caused by these detergents, phosphate builders are gradually being replaced with chemicals known as zeolites - complex compounds of aluminium, silicon and oxygen. Zeolites are effective as they soften water and reduce occurrences of eutrophication. When added as sodium zeolates in detergent, it replaces calcium ions in the water but the disadvantage is that they are not as effective in removing magnesium ions. Thus to obtain optimal water softening, a co-builder (usually a polycarboxylate) is used.

6. The Solvay process has been in use since the 1860s

identify the raw materials used in the Solvay process and name the productsCaCO3 + 2NaCl → Na2CO3 + CaCl2

Calcium carbonate (lime) + saturated brine → Sodium carbonate + Calcium Chloride

describe the uses of sodium carbonateSodium carbonate is used in the production of:

o Glass It is heated with silica (sand) and calcium carbonate to over 1500ºC where

sodium and calcium carbonates decompose into their oxides. These oxides combine with silica to form silicates which is found in glass.

o Soaps and Detergents – used as a replacement for NaOH Sodium carbonate is often reacted with calcium hydroxide to produce sodium

hydroxide which is used to produce soap. Using sodium carbonate is a cheap and efficient process.

o Used to soften hard water as carbonate ions precipitate magnesium and calcium. Hard water consists of excessive amounts of calcium and magnesium ions.

This is a huge problem when soap is in water as the anion in soap reacts with these ions to produce unwanted grey precipitates – scum. Thus sodium carbonate can be added to the soap to precipitate out the calcium and magnesium ions, which enhances soap’s cleaning ability.

o Baking soda production Sodium carbonate can be reacted with carbon dioxide to produce sodium

hydrogen carbonate (NaHCO3) which is used as baking soda, in chemical spills and in fire extinguishers.

o Standard base in volumetric analysis Pure, anhydrous sodium carbonate is often used as a primary standard in

volumetric analysis – e.g. in titrations where it can be used to determine the concentration of an acidic solution.

identify, given a flow chart, the sequence of steps used in the Solvay process and describe the chemistry involved in:

STEP 1: Brine purification + addition of ammonia

Brine is concentrated sodium chloride solution and is mostly found in the ocean’s salt water. Brine contains many impurities which are undesirable in the Solvay process. These may include calcium and magnesium ions. To remove these impurities there are two methods:

Precipitating out the ions by reacting it with either sodium carbonate or sodium hydroxide.

Ca2+ (aq) + CO3

2- CaCO3 (s)

Mg2+ (aq) + 2OH-

(aq) Mg(OH)2 (s)

Fractional crystallisation – where the more soluble contaminants are crystallised out from the brine solution.

Now this purified brine is entered into a vessel called an ammonia saturator. Here the brine flows down over many partitions in the ammonia saturator and ammonia (mainly from the Haber process), is passed up the tower thus dissolving in the brine. The solution is cooled by ice-cooled water and the result is the formation of ammoniated brine.

STEP 2: Production of sodium hydrogen carbonate

This ammoniated brine is passed into the Solvay tower (also called the carbonator). Here there is a reaction between the ammoniated brine (consisting of ammonia, water and sodium chloride) with carbon dioxide which is bubbled through. This carbon dioxide comes from the decomposition by heat of limestone (calcium carbonate) in a furnace:

CaCO3 (s) CaO (s) + CO2 (g)

HEAT

The carbon dioxide reacts with water to produce weak carbonic acid which in turn neutralises ammonia to form ammonium and hydrogen carbonate ions. These hydrogen carbonate ions react with sodium ions (from the salt) to produce sodium hydrogen carbonate (NaHCO3). The reaction mixture is cooled to about 0ºC which allows the aqueous sodium hydrogen carbonate to crystallise out leaving ammonium chloride in solution. The overall reaction for this step is:

NH3 (g) + NaCl (aq) + H2O (l) + CO2 (g) NH4Cl (aq) + NaHCO3 (s)

STEP 3: Formation of sodium carbonate

The solution in the previous step is filtered leaving the filtrate of ammonium chloride. The solid sodium hydrogen carbonate is collected and heated in a furnace to about 300ºC. This results in the formation of sodium carbonate, water and carbon dioxide. The carbon dioxide is recycled and reused as it is entered into the Solvay tower for the production of NaHCO3.

2NaHCO3 (s) Na2CO3 (s) + CO2 (g) + H2O (l)

HEAT

STEP 4: Recovery of ammonia The calcium oxide (lime) which was produced in step 2, is reacted with water to form calcium hydroxide (slaked lime). This is shown in the equation below:

CaO (s) + H2O (l) Ca(OH)2 (s)

Now refer back to the ammonium chloride filtrate which was also produced in step 2. This is reacted with the calcium hydroxide to regenerate ammonia:

Ca(OH)2 (s) + 2NH4Cl (aq) CaCl2 (aq) + 2NH3 (g) + 2H2O (l)

discuss environmental issues associated with the Solvay process and explain how these issues are addressed

Disposal of calcium chloride

Calcium chloride is a waste product in the Solvay process and it’s produced in large amounts. In some cases, the Solvay plant would sell this waste calcium chloride to industries where it would be used as a concrete additive, drying agent or to melt ice on the roads. However the major problem is that the supply of calcium chloride heavily outstrips the demand for it. As a result, the Solvay plant is forced to dispose of it at nearby landfills or waterways.

However this increases the level of dissolved salts in waterways, resulting in significant impacts for the local ecosystems. The aquatic plants and organisms may not be able to cope with this rise in chloride ion concentration. It causes destruction of vegetation in the area and also erosion. As a result, Solvay plants have addressed this issue by evaporation to dryness of the waste (more expensive method) and disposal in specially designed burial sites.

Heat release/thermal pollution

Overall, the Solvay process is an exothermic reaction thus excessive amounts of heat are released into the atmosphere and waterways. This can cause thermal pollution and significant impacts on organisms – especially in waterways. Thermal pollution arises from a significant temperature rise (of about 5-10ºC). This temperature change can cause the destruction of fish eggs and broadly the deaths of aquatic organisms such as frogs and crab + fall in levels of dissolved oxygen. In order to reduce this problem, the Solvay plants dilute their waste water, water from nearby lakes and rivers are added to cool the wastes or expensive heat diffusers are used.

Mining

The raw materials for the Solvay process are limestone (calcium carbonate) and brine. In order to obtain these materials, mining needs to be undertaken. This could have environmental implications such as the destroying of natural habitats and pollution. To combat this problem, Solvay plants are looking for other sources for these raw materials e.g. brine from the ocean.

Ammonia loss

Although ammonia in the Solvay process is recycled and reused, there are still noticeable amounts of ammonia released into the atmosphere. This is a problem as ammonia is a toxic gas which when inhaled can cause respiratory problems such as asthma and bronchitis. Thus to reduce this problem, Solvay plants implement good design and careful monitoring.

Dust

Dust is a problem for people in the vicinity of the Solvay plant and can cause allergies and respiratory problems such as asthma and bronchitis. This is being addressed by improving truck loading facilities and upgrading dust suppression systems in the plant.

perform a first-hand investigation to assess risk factors and then carry out a chemical step involved in the Solvay process, identifying any difficulties associated with the laboratory modelling of the step

We modelled the production of sodium hydrogen carbonate. We obtained a solution of ammoniated brine, dry ice (source of carbon dioxide) and a conical flask.

Method:

I. Obtained a 500mL conical flask. II. Add 200mL of ammoniated brine to the conical flask.

III. Add 2 spoonfuls of dry ice into the flask and quickly close the fume cupboard. IV. Repeat experiment.

Safety:

o Wear safety goggles to prevent poisonous aqueous ammonia from entering into eyes causing burns + irritants.

o Conduct experiment in a fume cupboard to prevent toxic ammonia gas from being released into the atmosphere. Ammonia is extremely discomforting to the upper respiratory tract + lungs and high exposure can cause unconsciousness, narcosis and may lead to death.

Difficulties:

Oversimplifies process. Some NaHCO3 crystals formed on the side of the flask. Only a very small amount of crystals formed. Small sample. Conducted in fume cupboard thus it was hard to see reaction.

Justify:

Dry ice was used as it was a source of carbon dioxide as well as allowing the contents in flask to cool enabling NaHCO3 crystals to form. Dry ice extremely cold at room temperature.

Reaction:

NH3 (aq) + NaCl (aq) + H2O (l) + CO2 (g) NaHCO3 (s) + NH4Cl (aq)

process information to solve problems and quantitatively analyse the relative quantities of reactants and products in each step of the process

PROBLEM 1: Find the masses of limestone and brine needed to produce 1 tonne (1000kg) of sodium carbonate?

STEP 1: WRITE EQUATION

CaCO3 (s) + 2NaCl (aq) Na2CO3 (s) + CaCl2 (aq)

STEP 2: FIND THE NUMBER OF MOLES OF SODIUM CARBONATE

Number of moles = mass (in grams) / molar mass = (1000000) / 105.99 = 9435 moles

Looking at the mole to mole ratio, NaCl: Na2CO3 = 2:1Therefore there are 18870 moles of NaCl.

STEP 3: FIND THE MASS

Using the equation n = m/M, the mass of NaCl = 1103 kg (or 1.1 tonnes). Now using the mole to mole ratio again, we can see that CaCO3: Na2CO3 is 1:1, therefore there are 9435 moles of limestone. Therefore the mass of limestone (calcium carbonate) needed = 944 kg (or 0.94 tonnes).

PROBLEM 2: During the preparation of calcium oxide, 1000kg of limestone (calcium carbonate) is heated. What mass of calcium oxide is produced and calculate the volume of carbon dioxide produced if the molar volume = 24.5L?

STEP 1: WRITE EQUATIONCaCO3 (s) CaO (s) + CO2 (g)

STEP 2: FIND THE NUMBER OF MOLES OF CALCIUM CARBONATE

The number of moles of calcium carbonate = (1000000) / 100.09 = 9991 moles. Using the mole to mole ratio, CaCO3: CaO is 1:1 therefore it also has 9991 moles.

STEP 3: FIND THE MASS

The mass of calcium oxide = (9991) x (56.08) = 560kg. Using the mole to mole ratio again, we can see that there is a 1:1 ratio between calcium carbonate and carbon dioxide. Therefore there are 9991 moles of carbon dioxide. Using the equation n = V/Vm, the volume of carbon dioxide produced = 245L.

use available evidence to determine the criteria used to locate a chemical industry using the Solvay process as an example

An ideal Solvay plant would be located in the following circumstances:o Near areas where raw materials such as limestone, salt and ammonia are readily available

and at a low cost i.e plant must be near Haber factory, or a limestone mine.

o On the coast with access to the ocean – for the safe discharge of calcium chloride waste away from rivers

o In an area with source of electricity and energy for the process – near coal mine etc. However, the availability of raw materials should take precedence over the availability of energy source as the process uses low energy.

o Where there are convenient connections to markets for the products of the Solvay process locally, domestically and internationally.

o Convenient links with transport for the transportation of raw materials to the factory and products from the factory

o Chemical factories should be located near towns or cities to ensure the availability of personnel for the plant

o Environmental issues must be considered – heat exchangers are to be established