Year 11 Chemistry ~ Unit 2 Area of Study 1. Water: Essential to Life Water is the most abundant liquid on Earth, covering over 70% of the planet.

Year 11 Chemistry ~ Unit 2

Area of Study 1

Water: Essential to Life

Water is the most abundant liquid on Earth, covering over 70% of the planet.

The Earth’s position in the solar system means that it gains the maximum benefit from the sun’s heat.

Water on Earth will neither boil or freeze.

Water: Essential to Life

Figure 10.2 For the space scientist, the presence of gaseous or frozen water in outer space is not an indicator of life, but the presence of liquid water would be considered as a positive sign. So far, however, none has been detected in outer space, which makes our home planet a unique place in the solar neighbourhood.

The Water Cycle

The water on Earth exist in solid, liquid and gas and can readily change from one state to another.

The water on earth changes state in order to transport it self around the planet.

This movement is called the water cycle.

Water and Living Things - Photosynthesis

Water is involved in the reactions of life: photosynthesis and respiration.

Photosynthesis is a reaction between water and carbon dioxide that forms glucose (energy source of all living things).

)(2)(6126)(2)(2 666 gslchlorophyl

gl OOHCCOOH

Respiration

As living things require energy, the glucose will react with oxygen in a process called respiration.

When respiration takes place, water that was removed from photosynthesis is returned to the water cycle.

)(2)(2)(2)(6126 666 glgs COOHOOHC

Water and Living Things

Water fulfils several other functions in plants and animals. Providing a transport system for

nutrients and soluble wastes. It provides a system to transfer heat. It provides a cooling system to the body.

The Propertiesof Water

Water exists as a liquid over a temperature range commonly found on Earth

Hydrogen bonds between water molecules - relatively strong compared to other intermolecular forces.

Strong hydrogen bonds give water a relatively high melting temperature compared to other molecules of similar size.

Polar molecule - difference in electronegativity between oxygen and hydrogen.

Polarity means it can dissolve many substances – Universal solvent (it such a good solvent….is not found pure in nature… LIKE DISSOLVES LIKE

Oils are non-polar which means they are insoluble – float on water.

Most gases have low solubility (decrease temp increase gas solubility)

High Melting and Boiling Temperatures

Water Expands on Freezing

When water freezes, the molecules form a lattice where each water molecule forms hydrogen bonds with four other molecules.

The hydrogen bonds take up a set amount of space.

As was melts, the water molecules are able to move closer together.

As such, the liquid will occupy less space than the solid.

High Latent Heat Values Latent heat measures the energy needed to change the

state of a substance at its melting and boiling temperature.

Latent heat of fusion is the energy needed to change a fixed amount of water from a solid to a liquid at 0°C.

Latent heat of vaporisation is the energy needed to change a fixed amount of water from a liquid to a gas at 100°C.

The higher latent heat means that more heat is needed to melt or boil water than for equivalent amounts of other substances.

High Latent Heat Values

High Heat Capacity

Water has the capacity to store a large amount of heat energy.

The specific heat capacity of a substance is the amount of heat energy needed to raise 1 gram of the substance by 1°C.

Water has a specific heat energy of

4.2Jg-1°C-1. When calculating the heat energy

(Joules, J) needed to heat a particular mass of a substance, the following formula can be used:

Heat energy = specific heat capacity x mass (g) x temperature change = SHC x m x ΔT

The Process of Dissolving

When one substance dissolves in another, the following processes occur: Solute particles are

separated. Solvent particles

separate from each other.

Solvent and solute particles attract each other.

Dissolves Polar covalent compound that can form hydrogen bonds with water(s) or (l) (aq)

Ionisation Polar covalent molecule.So highly polarised due to electronegativity that the covalent bond breaks

The dipole–dipole attraction between the molecules of water and hydrogen chloride leads to the breaking of the polar covalent bond between the hydrogen and chlorine atoms.

Dissociation Ionic solids in a 3D ionic latticePositive cations and negative anions separate from each other+ and – ions are more attracted to water due to the ion-dipole attraction so water pulls them out of their bonds.Not all ionic compounds are soluble because the energy required to break the bonds within the lattice is much greater than the energy that the water molecules can provide.

Dissolve, Dissociate or Ionise?? A substance will dissolve in water if is polar or can form ionic particles.

)(52)(522

aqOH

l OHHCOHHC

)(3)()(32 22aqaq

OHs COKCOK

Chapter 11

Solubility Guide

Measuring Solubility

The solubility of a substance refers to the maximum amount that can be dissolved in a given amount of solvent at a certain temperature.

A solution in which no more solute can be dissolved is said to be saturated.

Solubilities can be measured and compared by determining the mass of a solute that will dissolve in 100g of solvent at a given temperature.

Solubility Curves

The relationship between solubility and temperature can be represented by a solubility curve.

Each point on the curve represents saturated solution.

Every point below the curve represents an unsaturated solution.

Every point above the curve represents a supersaturated solution.

Crystallisation

As a solution cools, some of the solute will no longer stay dissolved and small crystals will form.

This is known as crystallisation.

Lower temperatures will decrease the solubility of a solute.

Solubility of Gases

Gases are much less soluble in water than most solids but their ability to be soluble is essential for the survival of aquatic life. Fish breathe the dissolved oxygen in water and plants rely on dissolved carbon dioxide.

The solubility of a gas depends on temperature of the liquid and the pressure of the gas.

As temperature increases, the gas becomes less soluble. This is evident by the small bubbles that form as you heat water.

Gas becomes more soluble as the pressure is increased.

Solubility of Gases

Temperature increase = Less solubleTemperature increase = Less soluble

Concentration of Solutions

The concentration of a solution is the amount of solute present compared to the amount of solution.

High amount of solute = concentrated. Low amount of solute = dilute.

Concentration of Solutions

Calculating Concentration

The concentration of a solution can be calculated by comparing the ratio of solute compared to solvent.

The most commonly used units for concentration are: Mass of solute per litre of solution Amount, in mol, of solute per litre of

solution.

Mass per Litre

When calculating the concentration of a solution in mass per litre we use:

)(__

__

Lsolventofvolume

soluteofmassionconcentrat

Amount per Litre

Measuring solubility in moles per litre is the most common method used by chemists.

This is also known as the molarity of a solution.

The units used are moles per litre or molar (M).

Amount per Litre

The molarity of a solution can be calculated using the following formula:

n = c x V

To convert to grams per litre, multiply by the molar mass.

Amount in mol

Concentration in molL-1 or M

Volume in L

Dilution

When more solvent is added to a solution, the action is described as dilution.

Even though the volume of the solution will change, the amount of solute remains the same.

Dilution will change the concentration of the solution.

Dilution

Because the number of moles of solute remains the same for both the original solution and the diluted solution, the concentration can be calculated using the following relationship:

c1V1 = c2V2Concentration and volume of the original solution

Concentration and volume of the diluted solution

Removing Dissolved Solutes

As mentioned earlier, water is an extremely effective solvent.

As such, it is very difficult to find pure water naturally.

There are a range of different ways we can purify water.

Chapter 12

Precipitation Reactions

Sometimes when two solutions are mixed a solid will form and separate from the solution.

This solid is called a precipitate. A precipitate is easily separated from a

solution through filtering. If a known impurity is in the water, it can be

removed by adding a solution that will form a precipitation reaction and the precipitate can then be filtered off.


When a substance dissolves in water it will dissociate into ions.

When two solutions are mixed together the ions from both solutions will also mix together.

At times, some of the cations and anions will attract each other to form an insoluble compound.



Figure 12.3 Possible exchange of ions in solution.

Balanced Chemical Equations

Reactions can be represented by writing balanced chemical equations.

1. Identify possible products of the reaction by swapping the cations and anions of the reactants.

2. Use a valency table to write the correct formulas of the reactants and products.

Balanced Chemical Equations

3. Write the equation and balance it so that equal numbers of all atoms occur on both sides.

4. Use the solubility table to deduce which of the products will form the precipitate and place the subscript (s) next to it to denote the state.

Ionic Equations

Because the ions in solution are dissociated, it is more accurate to write ionic equations.

When writing ionic equations, you can see that only some ions undergo a change and others remain the same on both sides of the equation.

These ions are often referred to as spectator ions and can be left out of the ionic equation.

Treatment of Drinking Water

Because of the amount of solutes dissolved in water and for the fact that water provides the environment for some bacteria to live, drinking water must go through a number of steps in order to make it suitable for drinking.

The first step in this process is flocculation where solids are removed and acids are neutralised.


Lime (Ca(OH)2) is added to the water to neutralise the acids.

Alum (Al2(SO4)3) is then added to form a precipitate with the hydroxide ions from the lime.

The gelatinous precipitate traps solids that are suspended in the water.

The water is then left for the solids to settle before they are removed.


The water is then filtered through a bed of sand and gravel to remove any other suspended particles.

The final step is chlorination. Gaseous chlorine is passed through the

water to destroy any bacteria. Some countries fluoridate their water by

adding fluoride ions. Fluoridation strengthens the enamel on the

teeth and helps to fight tooth decay.



Desalination

Desalination is the practice of collecting sea water and removing the salts to make it suitable for drinking.

One method of removing the salts in water is distillation.

Distillation involves the evaporation of water to separate it from the salts before condensing the steam and collecting the pure water.

Distillation is a very expensive process is not practical to be used to desalinate water on a large scale.

Desalination

Desalination

Osmosis is the natural tendency for water to move from a region of low salt concentration to a region with high salt concentration.

This process can be reversed if the salt water is placed under high pressure.

During reverse osmosis, the salt water and fresh water are separated by a semipermiable membrane that allows the water through but not the dissolved ions.

Desalination

Reverse osmosis is more suitable for large scale desalination plants.

The only difficulty being finding a suitable membrane that will not rupture under pressure.

Chapter 13

Introducing Acids and Bases

Acids and the related compounds called bases are very commonly used within our homes.

Acid comes from the Latin ‘acere’, which means 'sour’.

In industry, solutions of acids are used extensively to produce a wide range of products such as fertilisers, drugs, explosives and plastics.

Acids

Properties of Acids

Taste sour Have relatively low pH. Tend to be corrosive. Acids change litmus (a blue vegetable

dye) from blue to red. Can conduct electricity when in

solution (Aqueous).

Bases

Acids react with bases in such a way that they will remove each other’s properties.

As such, they are said to neutralise each other.

Bases can be found in many household cleaning products because they react fats and oils to form water-soluble soaps.

Bases

Properties of Bases

Taste bitter Feel slippery or soapy Have a relatively high pH. Are Caustic (Corrosive) Bases don't change the color of litmus; but

they can turn red (acidified) litmus back to blue.

Can conduct electricity when in solution.

Safety with Acids and Bases

Acids and Bases need to be treated with caution:

Avoid contact with skin and eyes, Wear safety glasses and lab coat, Label all bottles and containers, When diluting acids, add the acid to

the water (not the water to the acid), Notify the teacher if a spill occurs.

Indicators

Indicators are often extracted from plant dyes and their colour changes with the pH of a solution.

A Universal indicator is a mixture of many indicators and changes through a range of colours from red to green to violet.

A pH meter can be used to determine the pH of solutions that do not change colour.

Indicators

Indicators

Indicators

Figure 13.3 The pigment extracted from red cabbage acts as an acid–base indicator. Here (left to right) it has been added to hydrochloric acid, sodium hydroxide solution and water.

Reactions of Acids and Bases

Acids and bases were originally grouped together because they have similar chemical behaviours.

When acids react they will usually form a salt (a metal cation and non-metal anion) and other products.

The salt will depend on what anion is formed from the acid.

Reactions of Acids and Bases

General Reaction Types Involving Acids – Type 1






General Reaction Types Involving Acids – Summary

BrØnsted-Lowry Acids and Bases

Johannes BrØnsted and Thomas Lowry described the reactions of acids as involving the donation of protons (H+)

A proton is a hydrogen atom that has lost its electron.

A substance is an ACID if it DONATES a proton (H+).

A substance is a BASE if it ACCEPTS a proton (H+).

BrØnsted-Lowry Acids and Bases

• It is a reciprocal relationship as the acid donates a proton to the base who accepts it.

• This is why acids and bases react together.

+ Cl -- (aq)

+ Cl -- (aq)

Acid

HCl (g) + H2O (g)

HCl (g) + H2O (g)

H3O+

H3O+

(aq)

(aq)

Base

H+

H+

Acid-Base Conjugate Pairs

If substances can be formed from each other by donating or accepting a proton they are said to be a conjugate acid-base pair.

Acid Base ConjugateAcid

+ Cl -- (aq)

+ Cl -- (aq)

HCl (g) + H2O (g)

HCl (g) + H2O (g)

H3O+

H3O+

(aq)

(aq)

ConjugateBase

Acid-Base Conjugate Pairs

The Hydrogen Ion

The Hydrogen Ion H+ (aq) (Proton) in a solution is also represented as H3O+ (aq).

This is called a hydronium ion and reacts in exactly the same way as the H+ ion.

Amphiprotic Substances

Some substances can act as acids or bases depending on what they are reacting with.

This means they can Accept AND Donate Protons.


Acid

Acid

Base

Base

Therefore HCO3- is Amphiprotic


Acid and Base Strength

Different acid solutions of the same concentrations do not have the same strength.

The tendency of an acid or base to accept or donate protons from water can be used as a measure of their strength.

Strong Acids

A Strong acid very readily donates a proton. If an acid readily donates all its protons

(H+’s) this means it completely ionises. Acids that completely ionise in solution are

called Strong Acids. Solutions containing strong acids would

contain ions only with virtually no unreacted acids remaining.

Strong acids are HCl, H2SO4, HNO3

Weak Acids

A Weak Acid only donates some of its protons.

This means it only partially ionises (or Dissociates) – or in other words, not every molecule breaks apart.

Acids that partially ionise in solution are called Weak Acids.

Weak acids are CH3COOH, HF

Strong and Weak Acids

Figure 14.6 (a) In a 1 M solution, hydrochloric acid is virtually completely ionised in water.(b) However, in a 1 M solution of ethanoic acid, only a small proportion of ethanoic acid molecules are ionised.

Strong and Weak Bases

Strong bases easily accept protons (or an H+).

Strong bases include OH-, HCO3-

Weak bases can accept protons (or an H+) but do not do so readily.

Weak Bases include ammonia (NH3).

Polyprotic Acids

Polyprotic Acids are acids that can donate more than one proton.

The number of protons an acid can donate depends on how many hydrogens it has to begin with.

Monoprotic acids donate only one proton. Diprotic acids donate two protons. Triprotic acids donate three protons.

Strength vs Concentration

It is important not to confuse the terms Strong and Weak with Concentrated and Dilute.

Strength is a measure of the ionisation of an Acid or Base.

Concentration is how much of an Acid or Base actually dissolves in a solution.

Strength vs Concentration

Acidic, Basic and Neutral Solutions

The acidity of a solution is a measure of the concentration of Hydrogen Ions (H+) present.

The higher the concentration of H+ ions the more acidic the solution.


Pure water will ionise slightly by acting as a very weak acid and a very weak base:

Pure water is said to be neutral because the concentration of the H+ and the OH- ions are both exactly the same – 10-7M

H2O(l) + H

2O(l) H

3O+(aq) + OH--

(aq)

H2O(l) + H

2O(l) H

3O+(aq) + OH--

(aq)


Acidic Solutions contain greater concentrations of H3O+ than OH-.

Neutral Solutions contain equal concentrations of H3O+ and OH-.

Basic Solutions contain lower concentrations of H3O+ than OH-.

Measuring Acidity

Experiments have shown that all aqueous solutions (aq) contain both H3O+ and OH- ions.

Their product is always 10-14.[H3O+] x [OH-] = 10-14

If either [H3O+] or [OH-] are increased, the other must decrease proportionally.

Measuring Acidity

A solution is: Acidic if [H3O+] > 10-7 and [OH-] <

10-7

Neutral if [H3O+] = 10-7 and [OH-] = 10-7

Basic if [H3O+] < 10-7 and [OH-] > 10-7

The pH Scale

The pH scale is a convenient way of indicating the acidity of a solution.

The strength of an acid is based on the [H3O+] but these values are often very small numbers.

The pH can be calculated by:

pH = -log[H+]

The pH Scale

The pH Scale

The pH Scale

Calculations Involving Reactions

A balanced chemical equation tells us the proportion of reactants that must react together to complete a chemical reaction.

The coefficients in a balanced equation give us the ratio of amounts of reactants and products.

Mole Ratios

For the reaction:

2 moles of H2 react with 1 mole of O2 to form 2 moles of water.

The amount of oxygen gas used will always be equal to half the amount of hydrogen used and half the amount of water produced.

2H2(g) + O

2(g) 2H

2O(g)

2H2(g) + O

2(g) 2H

2O(g)

Stoichiometry

Stoichiometry is the term used for using mole ratios to calculate relative amounts of reactants used or products formed.

If a quantity of either a reactant or product is known, the quantities of all other reactants and products can be calculated using stoichiometry.

Stoichiometry

The following steps outline the stoichiometric process:

Step 1 – Write a balanced equation. Step 2 – Calculate the amount (in mol) of the

substance with the known quantity. Step 3 – Use the mole ratio to calculate the

amount of the required substance. Step 4 – Calculate the quantity required.

Excess Reactants

In most situations the amounts of reactants will not be exactly the amount required to react completely.

It is more than likely that one of the reactants will be used up before the other.

The reaction stops when one of the reactants (the limiting reagent) is used up even though some of the other substance is unreacted.

The other substance is said to be in excess.

Excess Reactants

It is important to identify the limiting reagent and the reactant that is in excess when doing calculations on a reaction.

All calculations must be centred around the limiting reagent.

Volumetric Analysis

The concentration of solutions of acids and bases can be determined accurately by a technique called volumetric analysis.

This involves reacting a solution with unknown concentration with a solution of accurately known concentration (a standard solution).

Volumetric Analysis

A volumetric analysis involves the following steps:

1. A pipette is used to dispense a known volume (aliquot) of the solution to be analysed into a conical flask.

2. An indicator is added to show when the equivalence point of the acid-base reaction is reached.

Volumetric Analysis

3. The standard solution is placed into a burette to be titrated (reacted) with the unknown solution.

4. The standard solution is titrated carefully with the unknown solution until the indicator changes colour and equivalence point is reached.

5. The volume (titre) is recorded and the process is repeated a number of times to ensure accuracy.

6. Stoichiometry is used to determine the unknown concentration.

Volumetric Analysis

Figure 15.7 The equipment needed to conduct a volumetric analysis: (a) volumetric flask; (b) pipette; (c) burette.

Oxidation and Reduction

Many of the chemical reactions that play a significant role in maintaining our environment are oxidation-reduction reactions or redox reactions.

Examples of redox reactions are the reactions that corrode metals, combustion reactions and photosynthesis and respiration.

Redox Reactions

Originally, oxidation was described as a reaction with oxygen.

When oxygen reacts with a substance, the substance is said to be oxidised.

A transfer of oxygen is referred to as redox reaction.

The substance that has gained oxygen has oxidised.

The substance that has lost oxygen has reduced.

Redox Reactions

Oxidation and reduction occur simultaneously during a redox reaction.

Consider the redox reaction:

Fe2O

3(s) + 3CO(g) 2Fe(s) + 3CO

2(g)

Fe2O

3(s) + 3CO(g) 2Fe(s) + 3CO

2(g)

Oxidation – gain of oxygen

Reduction – loss of oxygen

Electron Transfer

Not all redox reactions involve the transfer of oxygen.

A more accurate description of a redox reaction is the transfer of electrons.

Oxidation is the loss of electrons. Reduction is the gain of electrons.

OIL RIGOxidation Is Loss Reduction Is Gain

Half Equations

Consider the Redox reaction:

)()(2)( 22 sgs MgOOMg

The magnesium will undergo oxidation by losing electrons to form magnesium ions:

eMgMg 22

22 24 OeO

The oxygen gas will undergo reduction by gaining electrons to form oxide ions:

Writing Overall Redox Equations

When writing equations for redox reactions we usually write the half equations first.

The number of electrons must be balanced so that both half equations contain the same amount of electrons.

All the reactants from both half equations are written on the left hand side of the equation while all the products are written on the right.

The electrons are cancelled out.

Copper and Silver Nitrate

Figure 16.4 Copper wire placed in a silver nitrate solution forms deposits of silver crystals.

Oxidants and Reductants

An oxidant (or oxidising agent) is a substance that causes another to be oxidised, and is itself reduced.

A reductant (or reducing agent) is a substance that causes another to be reduced, and is itself oxidised.

Oxidants and Reductants

Classifying Redox Reactions

It is relatively easy to identify whether half equations are either oxidation or reduction reactions but sometimes it is not so easy to identify full equations as redox reactions.

Redox reactions can be identified by observing a change in Oxidation Numbers of the substances involved.

Oxidation Number Rules

Oxidation numbers are determined using the following rules:

1. Free elements have an oxidation number equal to 0. Eg Na(s), C(s), Cl2(g).

2. In ionic compounds the oxidation number s equal to the charge on the ion. Eg CaCl2: Ca2+=+2 and Cl- = -1.

3. Oxygen usually has an oxidation number of -2 and hydrogen has +1 but there are a few exceptions.

Oxidation Number Rules

4. The sum of oxidation numbers in a neutral compound is 0 and in a polyatomic ion is equal to the charge of the ion.

Using Oxidation Numbers to Identify Redox Reactions

By defining oxidation numbers for the atoms involved in a reaction we can look for increases and decreases in oxidation numbers.

An increase in oxidation number means the element has undergone oxidation.

A decrease in oxidation number means the element has undergone reduction.

Example

For the reaction:

)(2)(2)( 22 ggg COOCO +2 -2 0 +4 -2

Carbon in the carbon monoxide has gone from +2 to +4 which means that oxidation has occurred.

Oxygen in the oxygen gas has gone from 0 to -2 which means that reduction has occurred.

As both oxidation and reduction have occurred the reaction is a redox reaction.

Writing Half Equations

Although most half equations are quite easy to write, some involving polyatomic ions can be more difficult.

The following steps will make balancing these half equations easier:

1. Balance all elements except O and H in the half equation.

2. Balance the O atoms by adding water. 3. Balance the H atoms by adding H+ ions. 4. Balance the charge by adding electrons (e)

and then add states.

Example

A green solution containing Fe2+ ions is mixed with a purple solution containing MnO4

- ions. Fe3+ and Mn2+ ions are formed.

Write a balanced equation for this reaction.

The half equation involving the iron ions is quite simple:

Fe2+(aq) Fe3+ + e-

Example

The half equation involving the manganese is a little more difficult:

Step 1: Balance all elements except for O and HMnO4

- Mn2+

Step 2: Balance O by adding waterMnO4

- Mn2+ + 4H2O

Step 3: Balance H atom by adding H+

MnO4- + 8H+ Mn2+ + 4H2O

Step 4: Balance the charge with electronsMnO4

- + 8H+ + 5e- Mn2+ + 4H2O

Example

To complete the full balanced equation we must balance the electrons in each half equation:

Fe2+ Fe3+ + e-

MnO4- + 8H+ + 5e- Mn2+ + 4H2O

5Fe2+ 5Fe3+ + 5e-

Combine the two equations:MnO4

- + 8H+ + 5e- + 5Fe2+ Mn2+ + 4H2O + 5Fe3+ + 5e-

Cancel out the electrons:MnO4

- + 8H+ + 5Fe2+ Mn2+ + 4H2O + 5Fe3+

(X5)

Evidence for Electron Transfer

When a redox reaction takes place, the results can be visible but it is not always possible to see the transfer of electrons.

To show the transfer of electrons the half reactions must be separated and joined by an external circuit.

A galvanometer can be placed within the circuit to measure the flow of electrons.

Such an experiment is called a galvanic cell.

Galvanic Cells

Figure 16.7 The apparatus used to demonstrate electron flow during oxidation–reduction reactions.

Galvanic Cells

Galvanic cells consist of two half cells. Each half cell must consist of an electrode

to conduct the electrons and an electrolyte in which ions are free to move through the solution.

Oxidation will occur in one half cell and reduction will occur in the other.

The electrode at which oxidation occurs is called the anode.

The electrode at which reduction occurs is called the cathode.

Galvanic Cells

The half cells are also connected by a salt bridge.

A salt bridge contains an ionic compound that allows ions to flow between the solutions to complete the circuit and prevent an over accumulation of charge.

Anions flow into the anode to balance out the positive charge formed from oxidation.

Cations flow into the cathode to balance out the negative charge formed from reduction.

Galvanic Cells

The Electrochemical Series

Chemists have constructed a table of half equations for redox reactions that can be formed in half cells in the order of their reactability or their ability to Oxidise. This is called the Electrochemical Series.

The elements that reduce most readily are at the top of the series.

The elements that are lower in the series are more likely to oxidise.

The electrochemical series is only valid for the conditions from which it was formed (standard conditions).

The Electrochemical Series

Predicting Redox Reactions

The series can be used to predict what will happen when two specific half cells are combined to form a galvanic cell.

The half cell that is higher in the series will reduce and the one lower will oxidise.

Predicting Redox Reactions

Green Chemistry

Many aspects of our life have been enhanced by chemistry and the chemical industry.

The production of new and improved products have extended life expectancies and made living more comfortable.

However, these new have sometimes come at a cost to the environment and to human health.

Laws and processes have been put in place to identify hazardous substances and to replace them with safer chemicals that will do the same job.

Green Chemistry

Figure 17.2 The stepwise process that leads to the scientific development, evaluation and possible replacement of a product designed to fill a particular need.

Development of CFCs

Chlorofluorocarbons (CFCs) have been identified as a group of compounds that are responsible for the deterioration of the ozone layer.

The ozone layer acts as a filter that prevents some UV light from reaching the Earth.

CFCs were used as a cheaper and safer alternative for refrigeration, air conditioning and as propellants for aerosol cans.

Development of CFCs

It was after some time that scientists discovered that in the presence of UV light, CFCs would react with and breakdown ozone in the ozone layer.

As a result, the frequency of skin cancer in some areas increased.

The use of CFCs became outlawed and the hunt for a more environmentally friendly alternative began.

Development of CFCs

Research determined that the chlorine atom in CFCs as the main factor in the reaction with ozone.

Hydrofluorocarbons (HFCs) were developed as an alternative and were found to be just as effective without the environmental impact.

Green Chemistry

Laws and treaties that were enacted to reduce global pollution were aimed at dealing with wastes after the had been produced.

Green Chemistry is a set of principles that evaluates the environmental impact of a chemical process.

The green approach is that the best way to minimise hazardous waste is not to produce it in the first place.

Principles of Green Chemistry

Year 11 Chemistry ~ Unit 2 Area of Study 1. Water: Essential to Life Water is the most abundant liquid on Earth, covering over 70% of the planet.

Documents

water cyclethe water

water molecules

frozen water

presence of liquid water

heat energy

freezingwhen water freezes

suns heat

latent heat of fusion