Water chemistry

WATER CHEMISTRY

Hardness of water: Water which does not produce lather with soap solution readily, but forms a white curd, is called hard water.

Hardness in water is that characteristic, which “prevents the lathering of soap”. This is due to presence of water of certain salts of calcium, magnesium and other heavy metals dissolved in it. When hard water is treated with soap does not produce lather and forms a white scum or precipitate, due to the formation of insoluble soaps of calcium and magnesium.

2C17H35COONa + CaCl2 (C17H35COO)2Ca + 2NaCl Sodium stearate Hardness Calcium stearate

Soap (insoluble)2C17H35COONa + MgCl2 (C17H35COO)2Mg + 2NaCl

Temporary hardness (Carbonate hardness):

It is caused by the presence of dissolved bicarbonates of calcium, magnesium and other heavy metals and carbonate of iron. Temporary hardness can be removed by boiling of water. Bicarbonates are decomposed into insoluble carbonates or hydroxides, which are deposited as a crust at the bottom of vessel on boiling the water.

Heat Ca(HCO3)2 --------- CaCO3 + H2O + CO2

Calcium bicarbonate Calcium carbonate (insoluble)

Mg(HCO3)2 --------- Mg(OH)2 + 2 CO2 Magnesium bicarbonate Magnesium hydroxide

Permanent hardness (Non-carbonate hardness):

It is due to the presence of chlorides and sulphates of calcium, magnesium, iron and other heavy metals. Unlike temporary hardness, permanent hardness is not destroyed on boiling.

Equivalents of calcium carbonate:

The concentration of hardness is expressed in terms of equivalent amount of CaCO3 , since this mode permits the multiplication and division of concentration, when required. The choice of CaCO3 in particular is due to its molecular weight is 100 (equivalent weight = 50) and moreover, it is the most insoluble salt that can be precipitated in water treatment.

Mass of hardness producing substanceThe equivalents of CaCO3 = ------------------------------------------- X 50

Equivalent weight of hardness producing substance

Units of Hardness:

i) parts per million (ppm): It is the part of calcium carbonate equivalent hardness per 106 parts of water.

i.e. 1 ppm = 1 part of CaCO3 eq. hardness in 106 parts of water.ii) Milligrams per litre (mg/L) is the number of milligrams of CaCO3

equivalent hardness present per litre of water.

1mg/L = 1 mg of CaCO3 eq. hardness of 1 L of water.

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But 1 L of water weighs = 1kg =1000g =1000 X 1000 mg= 106 mg.

Therefore, 1mg/L = 1mg of CaCO3 eq per 106 mg of water.

= 1 part of CaCO3 eq per 106 parts of water =1ppm

Determination of temporary & permanent hardness of water by EDTA method:

It is a complexometric method.

Ethylene diamine tetra acetic aced (EDTA):

In the form of its sodium salt yields the anion:

Which form complex ions with Ca2+ and Mg2+

or MY2-

Where M= Ca or Mg.

In order to determine the equivalence point, indicator erochrome black-T or EBT (an alcoholic solution of blue dye) is employed, which form unstable wine-red complex with Ca2+ and Mg2+ ions. However, this indicator is effective at a pH of about 10. When EBT is added to hard water buffered to a pH of about 10 by employing NH4OH+NH4Cl buffer, a wine-red unstable complex is formed.

pH=10M2+ + EBT ---------- [M-EBT] complex

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So initially a wine-red coloured complex is obtained. During the course of titration against EDTA solution, EDTA combines with M2+ (Ca2+ or Mg2+) ions form stable complex M-EDTA and releasing free EBT, which instantaneously combines with M2+ ions still present in the solution, thereby wine-red colour is retained.

titration[M-EBT] complex + EDTA -------- [M-EDTA] complex + EBT (Wine-red) (Blue)

M2+ + EBT --------- [M-EBT] complex Blue wine-red

However, when nearly all M2+ ions have formed [M-EDTA] complex, then next drop of EDTA added displaces the EBT indicator from [M-EBT] complex and wine-red colour changes to blue colour (due to EBT). Thus, at equivalent point,

[M-EBT] complex + EDTA -------- [M-EDTA] complex + EBT (blue)

Thus, change of wine-red colour to distinct blue marks the end-point of titration.

Various steps involved in this method are:

1. Preparation of standard hard water: dissolve 1.0 of pure, dry CaCO3 in minimum quantity of dilute HCl and then evaporate the solution to dryness on a water bath. Dissolve the residue in distilled water to make 1 L solution. Each mL of this solution thus contains 1 mg of CaCO3 eq hardness.

2. Preparation of EDTA solution: dissolve 4 g of pure EDTA crystals + 0.1 g MgCl2

in 1 L of distilled water.

3. Standardization of EDTA solution: Rinse and fill the burette with EDTA solution. Pipette out 50mL of standard hard water in a conical flask. Add 10-15 mL of buffer solution and 4 to 5 drops indicator. Titrate with EDTA solution, till wine-red colour changes to clear blue. Let volume used be V1 mL.

4. Titration of unknown hard water: Titrate 50 mL of water sample just in above step. Let the volume used be V2 mL.

5. Titration of permanent hardness: take 250mL of the water sample in a large beaker. Boil it till the volume is reduced to about 50mL. Filter, wash the precipitate with distilled water, collecting filtrate and washings in 250mL measuring flask. Finally make up the volume to 250mL with distilled water. Then, titrate 50mL of boiled water sample just as in above step. Let volume used be V3 mL.

Calculations:

50mL of standard hard water = V1 mL of EDTA

=> 50 X 1 mg of CaCO3 = V1 mL of EDTA

1 mL of EDTA = 50/ V1 mg of CaCO3 eq

Now 50mL of given hard water = V2 mL of EDTA

= V2 X 50 / V1 mg of CaCO3 eq

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In 1 L (water 1000mL) of given hard = 1000 V2 / V1 mg of CaCO3 eq

total hardness of water = 1000 V2 / V1 mg/L

= 1000 V2 / V1 ppm

Now 50mL of boiled water = V3 mL of EDTA

= V3 X 50 / V1 mg of CaCO3 eq

1000mL(1L) of boiled water = 1000 V3 / V1 mg of CaCO3 eq

Permanent hardness = 1000 V3 / V1 ppm

And Temporary hardness = [Total hardness – Permanent hardness]

ALKALINITY

Alkalinity of water is measure of acid-neutralizing ability. It is attributed to the presence of the caustic alkalinity (OH- and CO3

2- ) and temporary hardness (HCO3-).

These can be estimated separately by titration against acid, using phenolphthalein and methyl orange as indicators. The determination is based on following reactions.

i) [OH-] + [H+] H2Oii) [CO3

2- ] + [H+] [HCO3-]

iii) [HCO3-] + [H+] H2O + CO2

The titration of the water sample against a standard acid upto phenolphthalein indicator end-point marks the completion of reactions i) & ii). This amount of acid used thus corresponds to hydroxide + one half of the normal carbonate present.

On the other hand titration of the water sample against a standard acid to methyl orange indicator endpoint marks the completion of i), ii) & iii).

Hence the amount of acid used after the phenolphthalein end point corresponds to one half of normal carbonate + all the bicarbonates; while the total acid used represents the total alkalinity ( due to OH- , CO3

2- and HCO3- ions).

The possible combinations of ions causing alkalinity in water are:i) OH- only orii) CO3

2- only oriii) HCO3

- only oriv) OH- & CO3

2- together orv) CO3

2- & HCO3- together

OH- + HCO3- CO3

2- + H2O

Thus, OH- & HCO3- ions cannot exist together in water. On the basis of same

reasoning, all the three ions (OH- , CO32- and HCO3

-) cannot exist together.

Procedure: pipette out 100ml water sample in a clean conical flask. Add to it 2 to 3 drops of a phenolphthalein indicator. Run N/50 HCl from a burette, till the pink colour is disappeared. Then to the same solution, add 2 to 3 drops of methyl orange , continue the titration, till the color changes yellow to orange pink.

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i) When P=0, both OH- & CO32- ions are absent, and alkalinity in that case

due to HCO3- only.

ii) When P=½M, only CO32- ion is present, since half of carbonate

neutralization reaction i.e. [CO32- ] + [H+] [HCO3

-] takes place with phenolphthalein indicator; while complete carbonate neutralization reaction i.e. [HCO3

-] + [H+] H2O + CO2 occurs when methyl orange indicator used. Thus, alkalinity due to CO3

2- = 2P.

iii) When P=M, only OH- is present, because neither CO32- nor HCO3

- is present, thus alkalinity due to OH- = M.

iv) When P > ½M, in this case, besides CO32- , OH- ions are also present. Now

half of CO32- equal to M-P; so alkalinity due to complete CO3

2- =2(M-P)Therefore alkalinity due to OH- = M - 2(M-P) = 2P – M.

v) When P < ½ M, ;in this case, besides CO32- , HCO3

- ions are also present now alkalinity due to CO3

2- = 2P.Alkalinity due to HCO3

- = (M-2P).

AlkalinityOH- ppm CO32- ppm HCO3

- ppm

P=0 0 0 M

P=½M 0 2P 0

P=M M 0 0

P > ½M 2P-M 2(M-P) 0

P < ½ M 0 2P M-2P

WATER SOFTENING METHODS

Ion exchange method: Removal of all ions present in water is called demineralization. The demineralization of water is done by using Ion exchange resins.

Ion exchange resin: Ion exchange resins are insoluble, cross linked, long chain organic polymers with a microporous structure. The ion exchange property of these polymers is due to mainly the functional groups attached to them. These functional groups may be acidic or basic. Based on functional groups the resins may be classified as: a) Cation exchange resins b) Anion exchange resins.

i) Cation exchange resins (RH+): They are mainly styrene-di vinyl benzene copolymers, which on sulphonation or corboxylation, -SO3H or –COOH groups are introduced to polymers. They become capable to exchange their H+ ions with the cation in water.

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ii) Anion exchange resins (R’OH-): They are styrene-di vinyl benzene or

amino-formaldehyde copolymers, which contain amino or quaternary ammonium or quaternary phosphonium or tertiary sulphonium groups as an integral part of the resin matrix. These, after treatment with dil.NaOH solution, become capable to exchange their OH- ion with the anions in water.

Basic or anion exchange resin (hydroxide form)

Process: It consists of two tanks. Cation resins and anion resins are kept in the 1st

and 2nd tank respectively. The hard water first is passed first through cation exchange column, which removes all the cations like Ca2+, Mg2+ etc. from it, and equivalent amount of H+ ions are released from this column to water.

2 RH+ + Ca2+ R2Ca2+ + 2 H+

2 RH+ + Mg2+ R2Mg2+ + 2 H+

After cation exchange column, the hard water is passed through anion exchange column, which removes all the anions like SO4

2-, Cl-, etc. present in the water and equivalent amount of OH- ions are released from this column to water.

R’OH-- + Cl- R’Cl- + OH-

2R’OH- + SO42- R’2SO4

2- + 2 OH-

2R’OH- + CO32- R’2CO3

2- + 2 OH-

The H+ and OH- ions released from both the column get combined to produce water molecule.

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H+ + OH- H2O

Thus, water coming out from the ion exchanger is free from cations as well as anions. Ion free water is known as deionized or demineralized water.

Regeneration: When capacities of cation and anion exchangers lost to exchange H+ and OH- ions, they are then said to be exhausted.

The exhausted cation exchange is regenerated by passing a solution of dil.HCl or dil.H2SO4.

R2Ca2+ + 2 H+ 2 RH+ + Ca2+ (washings)

R2Mg2+ + 2 H+ 2 RH+ + Mg2+ (washings)

The column is washed with deionized water and washings which contain Ca2+, Mg2+ , SO4

2- , Cl- ions is passed to sink or drain.

The exhausted anion exchange column is regenerated by passing a solution of dil.NaOH.

R’2SO42- + 2 OH- 2R’OH- + SO4

2- (washings)

R’2CO32- + 2 OH- 2R’OH- + CO3

2- (washings)

R’Cl- + OH- R’OH-- + Cl- (washings)Advantages:

The process can be used to soften highly acidic or basic waters.

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It produces water of very low hardness (2ppm), so it is very good for treating water for use in high pressure boilers.

Disadvantages:

The equipment is costly and more expensive chemicals are needed.

If water contains turbidity, then the out put of the process is reduced. The turbidity must be below 10ppm. If it is more it has to be removed first by coagulation and filtration.

Reverse osmosis: When two solutions of unequal concentrations are separated by a semi permeable membrane (does not permit the ions, atoms, molecules etc.), flow of solvent takes place from dilute to concentrated sides.

If, however, a hydrostatic pressure in excess of osmotic pressure is applied on the concentrated side, the solvent flow reverses, i.e. solvent is forced to move from concentrated side to dilute side across the membrane. This is the principle of reverse osmosis.

Thus, in reverse osmosis process methods pure water is separated from its contaminants, rather than removing contaminants from the water.

This membrane filtration is some times also called “super-filtration” or “Hyper filtration”.

Method : In this process, pressure of the order 15 to 40 kg cm2- is applied to the sea water/ impure water to force its pure water out through the semi permeable membranes; leaving behind the dissolved solids.

The membrane consists of very thin film of cellulose acetate, affixed to either side of a perforated tube. However, more recently superior membranes made of polymethacrylate and polyamide polymers have come into use.

Advantages: Reverse osmosis process is a distinct advantage of removing ionic as well as

non ionic, colloidal and high molecular weight organic matter.

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It removes colloidal silica, which is not removed by demineralization. The maintenance cost is almost entirely on the replacement of the semi

permeable membrane. The life time of membrane is quite high, about 2years. The membrane can be replaced within a few minutes, there providing

uninterrupted water supply. Due to low capital cost, simplicity, low operating cost and high reliability, the

reverse osmosis is gaining ground at present for converting sea water into drinking water and for obtaining water for very high pressure boilers.

Specifications of potable water:

Textile industry needs frequent dying of clothes, and the water used by this industry should be soft and free from organic matter. If hard water used uniform dying is not possible. Because hard water decrease the solubility of acidic dyes. Basic dyes even precipitate out in such hard water. Organic matter imparts foul smell. If the matter contains Fe, Mn, color or turbidity it causes uneven dyeing and leaves stains on fabrics. Hence, water should be free from these impurities.

Laundries require soft water, free from color, Mn and Fe. Because hardness increases consumption of soaps. Salt of Fe and Mn impart grey or yellow shade to the fabric.

Boilers require water of zero hardness otherwise efficient heat transfer is prevented by scale formation. Untreated water can also lead to corrosion of boiler material, some times even explosion can also occur.

Paper industry requires water free from SiO2, turbidity, alkalinity and hardness. SiO2

produces cracks in the paper. Turbidity, Fe & Mn affects the brightness and color of the paper. Alkalinity consumes alum and increase the cost of paper. Hardness increases the ash content of the paper.

Beverages require water which should not be alkaline as it destroys or modifies the taste as it tends to neutralize the fruit acid.

Sugar industry If hard water is used in sugar refining it results in the formation of deliquescent sugar. More over, these impurities cause difficulty in the crystallization of sugar.

Cooking water used should be free from dissolved salts producing hardness. Fuel requirement is high if hard water is used. More over, more time is required for cooking. Also if hard water is used for making tea or coffee, it imparts unpleasant taste and muddy-looking extract.

Dairies and pharmaceutical industries require ultra pure water which should be colorless, taste less, odorless and free from pathogenic organism.

DISINFECTION OF WATER

CHLORINATION: chlorination is the most commonly used disinfectant in water treatment throughout world. It can be employed directly as gas or in the form of concentrated solution in water. It produces hypochlorous acid, which is a powerful germicide.

Cl2 + H2O HOCl + HCl Bacteria + HOCl Bacteria are killed

Death of micro-organism, bacteria etc. results from chemical reaction of hypochlorous acid with the enzymes in the cells of organism etc. Since enzyme is

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essential for the metabolic processes of the micro-organism, so death of micro-organism results due to inactivation of enzyme by hypochlorous acid.

Apparatus used for disinfection by chlorine is known as chlorinator. It is a large tower which contains number of baffle plates. From its top, raw water and proper quantity chlorine solution are introduced. These get thoroughly mixed during their passage through the water. For filtered water, about 0.3 to 0.5ppm of Cl2 is sufficient. Disinfected water is taken out from the out let at the bottom of chlorinator.

Factors affecting efficiency of chlorine:

i) Temperature of water: the rate of reaction with enzymes increases with temperature. Consequently, death rate of micro-organisms by chlorine increases with rise in temperature.

ii) Time of contact: death rate of micro-organisms by chlorine is proportional to the number of micro-organisms remaining alive. Initially, the death rate is maximum and with time, it goes on decrease.

iii) pH of water: at lower pH values (between 5 – 6.5), a small contact is required to kill organisms.

Advantages of chlorination:

i) it is effective and economical.ii) It is stable, require small space for storage, and does not deteriorate on

keeping.iii) It can be used at high as well as low temperatures.iv) It does not introduce any impurity in water.v) It is most ideal disinfectant.

Disadvantages:

i) excess of chlorine, produces bad taste and disagreeable odor.ii) Excess chlorine produces irritation on muscus membrane. The quantity of

free chlorine in treated water should not exceed 0.1 to 0.2ppm.iii) It is more effective below pH 6.5 and less effective at higher pH vales.

Break-Point chlorination: It means that chlorination of water to such an extent that living organisms as well as other organic impurities in water are destroyed. It

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involves in addition of sufficient amount of chlorine to oxidize organic matter, reducing substances and free ammonia in raw water, leaving behind mainly free chlorine which possesses disinfecting action against pathogenic bacteria’s. It is also known as free-residual chlorination.

Initially for lower doses of Cl2 , there is no free residual chlorine since all the added chlorine gets consumed for doing complete oxidation of reducing substances present in water.

As the amount of chlorine dosage is increased, amount of residual chlorine also show steady increase. This stage corresponds to the formation of chloro-organic compounds without oxidizing them.

At still higher dose of applied chlorine, oxidation of organic and micro-organisms gets in consequently the amount of free residual chlorine also decrease. When the oxidative destruction is completed it reaches minima.

After minima, the added chlorine is not used in any reaction. Thus, the residual chlorine keeps increasing in proportion to added chlorine. Hence, for effectively killing micro organisms, sufficient chlorine has to be added. Addition of chlorine in such dosages is known as break-point or free residual chlorination.

Advantages: it ensures complete destruction of organic compound which impart color, bad odor and unpleasant taste to water. It completely destroys all the disease causing bacteria. It prevents the growth of any weeds in water.

De-chlorination: Over chlorination after the break point produces unpleasant taste and odour in water. These objectionable qualities may be removed by filtering the over-chlorinated water through a bed of molecular carbon. Alternatively, a small percentage of activated carbon may be added directly to the water and after allowing a short reaction period, it is then removed by filtration. Objectionable qualities resulting from over-chlorination may also be remedied by the addition of a small percentage of sulphur dioxide or sodium sulphate or sodium thiosulphate, etc.

SO2 + Cl2 + 2H2O H2SO4 + 2HCl

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Na2SO3 + Cl2 + 2H2O Na2SO4 + 2HCl

OZONATION: Ozone is a excellent disinfectant. It is produced by passing silent electric discharge through cold and dry oxygen.

Silent electric current3O2 --------------- 2O3

Ozone is highly unstable and breaks down, liberating nascent oxygen.

O3 - O2 + [O] nascent

The nascent oxygen is very powerful oxidizing agent and kills all the bacteria as well as oxidizes the organic matter present in water.

For carrying out the disinfection by ozone, ozone is injected into the water and the two are allowed to come in contact in a sterilizing tank. The disinfected water is removed from the top. The contact period is about 10-15 minutes and the usual dose strength 2-3ppm.

Advantages: removes colour, odour and taste without giving residue, not harmful, since it is unstable an decompose into oxygen.

Disadvantage: quit expensive.

BOILER TROUBLES(Boiler Scales)

In boilers, water evaporates continuously and the concentration of the dissolved salts increases progressively. When their concentrations reach saturation point, they are thrown out of water in the form of precipitates on the inner walls of the boiler.

If the precipitation takes place in the form of loose and slimy precipitate, it is called sludge. On the other hand, if the precipitated matter forms a hard, adhering crust/coating on the inner walls of the boiler, it is called scale.

Sludge is a soft, loose and slimy precipitate formed within the boiler. Sludge can easily be scrapped off with a wire brush. It is formed at comparatively cold portions of the boiler and collects in areas of the system, where the flow rate is slow or at bends. Sludges are formed by substances which have greater solubilities in hot water than in cold water. E.g. MgCO3, MgCl2, CaCl2, MgSO4, etc.

Scales are hard deposits, which stick very firmly to the inner surfaces of the boilers. Scales are difficult to remove, even with the help of hammer and chisel. Scales are the main source of boiler troubles.

Formation of scales may be due to:

i) Decomposition of calcium bicarbonate:

Ca(HCO3)2 CaCO3 + H2O + CO2 Scale

However, scales composed chiefly of calcium carbonate is soft and is the main cause of scale formation in low-pressure boilers but in high-pressure boilers, CaCO3 is soluble.

CaCO3 + H2O Ca(OH)2 (soluble) + CO2

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ii) Deposition of calcium sulphate: The solubility of calcium sulphate in water decreases with rise of temperature. Thus, solubility of CaSO4 is 3,200 ppm at 150C and it reduces to 55 ppm at 2300C and 27 ppm at 3200C. In other words, CaSO4 is soluble in cold water, but almost completely insoluble in super-heated water. Consequently, CaSO4 gets precipitated as hard scale on the heated portion of the boiler. This is the main cause of scales in high-pressure boilers.

iii) Hydrolysis of magnesium salts: Dissolved magnesium salts undergo hydrolysis forming magnesium hydroxide precipitate, which forms a soft type of scale.

MgCl2 + 2H2O Mg(OH)2 + 2HCl Scale

iv) Presence of silica: SiO2, even present in small quantities, deposits as calcium silicate and magnesium silicate. These deposits stick very firmly on the inner side of the boiler surface and are very difficult to remove. One important source of silica in water is the sand filter.

Effects of scales:

Scales have a low thermal conductivity, so the rate of heat transfer from boiler to inside water is greatly decreased. In order to provide steady supply of heat to water, excessive or over heating is done and this causes increase in fuel consumption.

The over-heating of the boiler tube makes the boiler material softer and weaker and this causes distortion of boiler tube and makes the boiler unsafe to bear the pressure of the steam, especially in high pressure boilers.

Scales may some times deposit in the valves and condensers of the boilers and choke them partially. This results in decrease in efficiency of the boiler.

When thick scales crack, due to uneven expansion, the water comes suddenly in contact with over-heated iron plates. This causes in formation of a large amount of steam suddenly. So sudden high pressure is developed, which may even cause explosion of the boiler.

Removal of scales:

If they are loosely adhering, with the help of scraper or piece of wood or wire brush.

If they are brittle, by giving thermal shocks. If they are adherent hard, by dissolving them by adding them chemicals.

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Some important questions:

1 List the essential requirements of potable water.

2 Name the salts responsible for the temporary and permanent hardness of water sample.

3 What is demineralization of hard water? Name the chemicals used to regenerate exhausted cation and anion exchangers.

4 Explain the principle behind the colour change from wine red to blue of the indicator in the EDTA titration of hardness estimation of water.

5 What do you mean by hardness of water? How is it classified?

6 What is EDTA? Write its structure and uses.

7 Name the substance (compound) responsible for disinfection during chlorination.

8 Define hardness of water? Why do we express hardness in terms of CaCO3.

9 What is the indicator used in EDTA method? What is the end point.?

10 Discuss the water softening by ion – exchange process.

11 What is Desalination? Discuss any one method of desalination of seawater.

12 Describe briefly the estimation of hardness of water sample by EDTA method.

13 A 100 ml sample of water contains 12 mg of MgSO4 (Mol. Wt. = 120) and 22.2 mg of CaCl2 (Mol.Wt. = 111). Calculate the hardness in ppm units.

14 What is a boiler scale? Explain how it is formed in the boiler.

15 Discuss briefly the role of cation and anion exchange resins in softening water.

16 A sample of water contains 21.9 mg of Magnesium bicarbonate, 19.0 mg of MgCl2 and 18 mg of MgS04 per litre. Calculate the temporary and permanent hardness of this sample (At. Wt Mg = 24, Ca = 40, S = 32, Cl = 35.5)

17 Explain how water is disinfected by chlorine. Mention the advantages and disadvantages of chlorination process.

18 100 ml of a sample of hard water required 15 ml of 0.01 M EDTA for titration using EBT indicator. 100 ml of sample was boiled and filtered. The filtrate is

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made upto 100 ml with distilled water. This made up solution required 8 ml of 0.01 M EDTA solution for titration. Calculate the total, permanent and temporary hardness of the sample of hard water in terms of ppm units.

19 What are scales and sludges in boilers? What are their disadvantages caused to boilers?

20 How the carbonate and bicarbonate alkalinity is determined experimentally in a water sample?

21 Water sample contains OH-

, HCO3-

& CO3-

, Cl-

, SO4- 2

. Which ion causes

alkalinity & why.

22 What is meant by break point chlorination? What is its significance in water treatment?

23 50 ml of water sample consumed 15 ml of N/50 HCl using phenolphthalein indicator. In another titration 50 ml of same water consumed 25 ml N/50 HCl with methyl orange indicator. Identify and calculate the type of alkalinity and express the same in CaCO3 equivalents.

24 What is reverse osmosis? How is sea water purified by this method?

25 50 ml of a sample of water consumed 20 ml of 0.01 M EDTA. The same water after boiling consumed 12 ml of same EDTA. Calculate total temporary and permanent hardness of water.

26 Describe the estimation of hardness of water sample by EDTA Method.

27 What happens if temporary hard water is boiled? Give equations.

28 What are the specification of potable water?

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