WATER Water is most abundant, useful & misused one It is universal solvent

Uses : Domestic purposes : Cooking, bathing, Drinking Industries : Boilers, Dye industries, cotton.

Sources :

1. Surface water

2. Underground water

1.Surface water :

1. Rain Water2. River Water3. Lake Water 4. Sea Water It is most impure form Continuous evaporation increases

concentration of impurities. Dissolved salts = 3.5 % NaCl = 2.6 %

2. Under Ground Water : Part of rain water, Reaches the earth, percolates into the earth. It comes in constant with a no of minerals

HARDNESS OF WATER

Characteristic of water which prevents lathering of soap

Due to the presence of salts of Ca, Mg & other heavy metals.

Hard water does not produce lather, from white scum or precipitate

Precipitate forms due to the formation insoluble soaps (Calcium stearate & magnesium stearate)

C17H35COONa + Ca+2 (C17 H35COO)2 Ca + Na+

C17H35COONa + Mg+2 (C17 H35COO)2 Mg + Na+

Types :1. Temporary (carbonate) Hardness2. Permanent ( Non carbonate ) Hardness 1.Temporary Hardness : (Carbonate) Caused due to the presence of dissolved

bicarbonates of Ca, Mg, Na, K. Destroyed by boiling.

Ca(HCO3)2 CaCO3 +CO2 + H2O

Mg(HCO3)2 Mg(OH)2 + CO2

2.Permanent hardness (Non Carbonate) : Caused due to the presence of Chloride,

Sulphates, Nitrates of Ca, Mg, and other metals. Can’t be removed by boiling.

Calcium Carbonate Equivalence : Hardness is expressed in calcium carbonate

equivalence. M.Wt. of CaCO3= 100 Most insoluble

cesubsproducinghardnessofweightEquivalentChemical

CaCOofweightequivalentchemicalcesubsproducinghardnessofMass

tan

tan 3

Units : 1 ppm = 1 part of CaCO3 present in 106parts of

water 1 mg/lit. = 1 mg of CaCO3 present in 1L of water

10Cl = 1 part of CaCO3 present in70,000 L of water (1 Gallon)

10 Fr = 1 part of CaCO3 present in 105 parts of water

1 ppm = 1mg/lit = 0.07 0C1 = 0.1 0Fr

EDTA method : (Complexometric method)

EDTA = Elthylene diamine tetra acetic acid

It exists as its di sodium salt

H+NN+H

-OOC

+Na-OOC

COO-

COO-Na+

H2C

CH2

Soap titration method

EDTA method

Estimation of Hardness

Principle : Equivalent point (end point ) is determined by eriochrome black

–T indicator (alcoholic solution of blue dye.) Indicator is effective at pH 10 Buffer used is (NH4OH – NH4Cl) to maintain pH

Colour change wine-red to blue

M+2 +EBT [M(EBT)]Hard water Wine –red(Unstable)

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

PROCEDURE:

Part: 1: Preparation of Standard Hard water: Transfer a known mass (about 10 mg)

of calcium carbonate into a 100ml volumetric flask. Add 40-50 ml(approximately) of water. Add dilute hydrochloric acid till a clear solution is obtained. Make up the volume to the mark by adding water.

Part:2: Standardization of EDTA:

Pipette out 10ml of Standard hard water, into a conical flask. Add 5ml (approx) of buffer and a few drops of Eriochrome black-T indicator. The solution attains wine-red colour. Titrate the contents of the conical flask against the solution of EDTA solution. Stop the addition of solution from the burette when the colour of solution in the conical flask changes from wine-red to blue. Note the burette reading and repeat the titration to get concurrent results. Let the volume of the solution of EDTA consumed in this titration be ‘V1’ ml.

Part:3: Determination of Total Hardness of Test Sample

of Water: Pipette out 10ml of test sample of water in the

conical flask. Add 5ml (approx) of buffer and 3 to 4 drops of Eriochrome black-T indicator. The solution attains wine-red colour. Titrate the contents of the conical flask against EDTA solution till the colour changes from wine-red to blue. Note the burette reading and repeat the titration to get concurrent results. Let the volume of EDTA solution consumed in this titration be ‘V2’ ml.

The total hardness of the test sample of water is calculated as follows:

Calculations: 1) 100ml of standard hard water = x mg of calcium

carbonate 1 ml of standard hard water = x/100 mg of calcium

carbonate 2) V1ml of EDTA solution = 10 ml of standard

hard water 1 ml of EDTA solution = 10/V1 ml of

standard hard water = (10/V1)((x/100)mg

of calcium carbonate = (x/10V1) mg of

calcium carbonate 3) 10 ml of test sample water = V2 ml of EDTA 1000 ml of test sample of water = 100 V2 ml of EDTA = 100 V2 (x/10V1)

mg of Calcium carbonate = (10 V2 x /V1) mg of

Calcium carbonate Total Hardness of test sample of water = (10 V2 x/ V1)

mg/litre

ANALYSIS OF WATER

ALKALINITY: Presence of anions, such as carbonates ,

bicarbonates and hydroxide results in alkalinity of water.

The estimation of water is done through the titrating water sample against standard acid using Phenolphthalein and methyl orange indicator.

Two indicators are used as the different anions to give end points at different PH values.

Out of three anions CO3-2, HCO3

-2 &

OH- out of the three anions any two of them can exist in water together( CO3

-2, OH- ),

(HCO3-2, CO3

-2)

HCO3-2 & OH- can’t be present together

because H+ ion of HCO- 3netutralises OH-.

HCO3– + OH–      CO3

-2 + H2O

Experimental procedure Hundred milliliter of water sample is taken and two

drops of phenolphthalein is added to it. The colour will become pink due to the PH value above 10.This sample of water is titrated with N/50 HCl solution. At the end pink colour disappears this end point termed as P- end point. Now add two drops of methyl orange indicator to the same water (PH>7). At the end point , pink colour disappears this end point known as M- end point /Methyl orange end point.

Reactions CO3-

2 + H+ HCO3-

HCO3-+ H+ H20 + CO2

OH- + H+ H2O Calculations:

The phenolphthalein alkalinity in terms of CaCO3 = P*50*106/50*100*1000=(10P)PPM

The alkalinity of methyl orange =M*50*106/50*100*1000=(10M)PPM

Result of Alkalinity P = 0  P < ½T  P=½T    P>½T        P = T

OH –

alkalinity0002P-TP=T

Carbonate Alkalinity02P2P2(T-P)0

Bicarbonate AlkalinityTT-2P000

Softening of water

It can be done by 2 methods

1) internal treatment.

2) external treatment.

Water used for industrial purposes sufficiently pure. The process of removing hardness producing

substances from water is called softening of water.1. Lime-Soda process: In this method soluble Ca & Mg salts in water are

converted in to insoluble compounds, by adding calculated amount of Lime and soda.

CaCO3 and Mg(OH)2, so precipitated, are filtered off.

EXTERNAL TREATMENT (SOFTENING METHODS)

Cold lime soda process: In this process calculated amount of chemicals (lime and

soda) are mixed with water at RT At RT the precipitates formed are finely divided, will not be

settle down easily. So, it is essential to add small amount of coagulants (Alum,

Sodium aluminate, Aluminium sulphate). These coagulants help in the fine precipitation. Sodium aluminate also helps the removal of silica and oil. This cold L-S process provides water-containing 50-

60ppm.

NaAlO2 + H2O NaOH + Al(OH)3Al2(SO4) 3+Ca(HCO3)2 Al(OH)3+ CaSO4+ CO2HOT LIME SODA PROSESS:It involves treating water with softening chemicals at a

temperature of 80-150oC The reactions proceed fasterSoftening capacity increasedPrecipitates and sludge formed settle down rapidly No coagulants are neededMuch of the dissolved gases driven out of the waterFiltration of softened water is fast

Advantages of Lime Soda process: Very economical. Lesser amount of coagulants is needed. This process increases the pH of water and

protects from corrosion. Mineral quantity is reduced.Disadvantages of Lime Soda process: Careful operation and skilled supervision is

required. Disposal of large amount of sludge is difficult. Removes hardness up to 15ppm.

2. ZEOLITE (PERMUTIT) PROCESS: Zeolite is hydrated sodium alumino silicate. It is also called as Permutits. It capable of exchanging its sodium ions Structure of sodium Zeolite is Na2O.Al2O3.xSiO2.yH2O. Where x = 2-10, y = 2-6

Zeolites are two types1.Natural Zeolites: These are non-porous.

Ex.: Na2O.Al2O3.4SiO2.2H2O

2.Synthetic Zeolites: These are porous and possess gel structure. These have higher exchange capacity Prepared by heating together china clay, faldspar

and soda.

Process: Na2Ze + Ca(HCO3)2 NaHCO3 + CaZeRegeneration: After some time the zeolite is converted in to Ca and Mg

Zeolites and it gets exhausted. At this stage the supply of this hard water is stopped and the

exhausted Zeolite is reclaimed by treating with 10% NaCl CaZe + 2 NaCl CaCl2 + Na2ZeLimitations: If the water is turbid, the suspended matter is to be removed. Large quantity of iron and manganese should be removed;

otherwise they form Mn and Fe Zeolites. if mineral acids are present, they may destroy the Zeolite bed.

Advantages:It removes the hardness up to 10ppm.The equipment used is very compact.No impurities are precipitated, so there is no formation of sludge or scale.It requires less time.It requires less skill.

Disadvantages: Treated water contains more sodium. It removes only positive ions. High turbidity water cannot be treated.

3.Ion Exchange Process: It is also called de-ionization or demineralisation. Ion exchange resins are in soluble, long chain,

cross-linked polymers with a micro porous structure.

Resins containing acid groups (COOH, SO3H) are capable of exchanging their H+ ions with other cations.

Resins containing basic groups (OH-, NH2-) are

capable of exchanging their OH- ions with other anions.

Cation exchange resin Anion exchange resin

For efficient separation ions-selective membranes are employed.

Ex. RCOO-, RSO3- and R4N+Cl-

Examples of resins:

Ion exchange process: The hard water is passes first through cation exchange

column, which removes all the cations like Ca+2,Mg+2 etc. from it, and equivalent amount of H+ ions are released from this column to water thus:

2RH+ + Ca+2 R2Ca+2 + 2H+

2RH+ + Mg+2 R2Mg+2 + 2H+

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 thus: ROH- + Cl- RCl-

2ROH- + SO4-2 2OH-

H+ & OH- ions get combined to produced water molecule.

H+ +OH- H2O Thus water coming from the exchanger is

free from cations as well as anions. Regeneration : Exhausted anion resin is

regenerated by dil. HCl , anion by dil.NaOH.

Internal treatment Internal treatment of boiler water is carried out by

adding proper chemicals to precipitate the scale forming impurities in the form of sludge and to convert the scale forming chemicals into sludges which can be removed by blow down process.

In other method problem causing cations converted in to compounds, which will stay in dissolved form in water and thus do not cause any harm.

Some of the internal treatment methods used for the removed of scale formation in boilers are.

Colloidal conditioning:

Scale formation can be avoided in low pressure boilers by adding substances like kerosene, tannin, agar-agar etc. which get absorbed over the scale forming precipices , there by yielding non-sticky and lose deposits which can be easily removed by blow down process.

Carbonate conditioning

In low pressure boilers, scale formation can be avoided by adding sodiunm carbonate to boiler water, when salts like CaSO4 can be converted into CaCO3 in equilibrium.

CaSO4 + Na2CO3 CaCO3 + Na2SO4

Calgon conditioning:

It involves in adding Sod. Hexameta phosphate (calgon) to boiler water to prevent the scale and sludge formation .

Calgon converts the scale forming impurity like CaSO4 into soluble complex compound.

Na2(Na4(PO3)6) 2Na+ + (Na4(PO3)6)-2

2CaSO4 + (Na4(PO3))-2 (Ca2(PO3)6) -2 + 2Na2SO4 solublecomplex

Phosphate conditioning

It is applicable to high pressure boilers scale formation is avoided by adding sod.phospate, which reacts with Mg,Ca salts forming non-adherent and easily removed by blow down process.

3MCl2 + 2Na3PO4 M3(PO4)2 + 6NaCl

3MSO4 + 2 Na3PO4 M3(PO4) + 6NaSO4

Where M= Ca+2 or Mg+2

The main phosphates employed are Sod.dihydrogen phosphate , disodium hydrogen phosphate , trisodium phosphate.

Treatment with Sodium Aluminates:

It gets hydrolyzed yielding NaOH & gelatinous ppt. of aluminum hydroxide. Thus:

NaAlO2 + 2H2O NaOH +Al(OH)3

The NaOH , so formed , ppts some of the Mg as Mg(OH)2

MgCl2 + 2NaOH Mg(OH)2 + 2NaCl.

The ppts are removed by blow down process.