water technology 3

8/2/2019 Water Technology 3

1/12

WATER TECHNOLOGY I

ANALYSIS OF WATER

Dr. E. LaxminarayanaMail: [email protected]

Alkalinity:

Due to the presence of Caustic alkalinity(OH-- & CO3

-2)

Temporary hardness(HCO3-)

These can be estimated by titration against standardacid

The determination is based on

1. OH- + H+ H2O

P2. CO3

-2 + H+ HCO3-

M3. HCO3

- + H+ H2O + CO2


2/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Reaction 1 &2 take place in presence ofPhenolphthalein indicator

All Reactions of Methyl orange indicator

In presence of phenolphthalein indicatorcomplete neutralization of hydroxide & halfneutralization of carbonate takes place.

After phenolphthalein end point completeneutralization of carbonate and all bicarbonates

takes place.


3/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


The possible combinations of alkalinity

OH

-

CO3-2

HCO3-

CO3-2 & HCO3

-

CO3-2 &OH-

OH- & HCO3- ions does not exist

CO3-2, OH- & HCO3

- ions does not exist


4/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Procedure:

100 ml of water sample

add 2-3 drops of phenolphthalein

titrate against N/50 acid from the burette

pink colour is discharged

continue the titration with methyl orange indicator


5/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


--2(M-P)2P-MP>M/2

M-2P2P--P


6/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Estimation of chloride:

Usually it presents as NaCl, MgCl2, CaCl2 Chloride conc. Over 250ppm is not desirable for drinking

It is estimated by titrating against standerd AgNO3

Potacium chromate is indicator

PH is 7-8

AgNO3 Ag+ + NO3-

Ag+ +Cl- AgCl (White)

Ag+ + CrO4-2 Ag2CrO4 (red)AgNO3 + K2CrO4 KNO3 + Ag2CrO4


7/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


K2CrO4 indicator is prepared by dissolving 5 gmsof K2CrO4 in 100 ml distilled water.

Procedure:

50 ml of given sample

add 1 ml of freshly prepared K2CrO4

titrate against AgNO3 from the burette while shaking

colour changes from yellow to red and red colour persists


8/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Blank Titration:

The above procedure is repeated with distilled waterCalculations:

Sample silver nitrate solution

V1N1 = V2N250 x N1 = V2 x 1/50

N1 = V2 x 1/2500

Strenth of chlorine = 35.5 x V2 x 1/2500 gm/L

=1000 x 35.5 x V2 x 1/2500 mg/L


9/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Dissolved oxygen

It is based on the oxidayion of KI by dissolved oxygen

Liberated Iodine is titrated against standard

sodiumthiosulphate using starch as final indicator O2 in water is not capable of reacting with KI, as an

Oxygen carrier (Manganese hydroxide) is used


10/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


KOH + MnSO4 Mn(OH)2 + K2SO4

Mn(OH)2 + O2 MnO(OH)2Basic manganic oxide

MnO(OH)2 + H2SO4 MnSO4 + H2O + (O)

KI + H2SO4+ (O) K2SO4 + H2O + I2

Na2S2O3 + I2 NaI + Na2S4O6


11/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Some times water may has nitrites sulphites and

undergo oxidation in presence of O2 This can be avoided by adding NaN3 to the water

sample

NaN3 + H2SO4 N3H + Na2SO4

HNO2 + N3H N2O + N2 + H2O


12/12

WATER TECHNOLOGY I

ANALYSIS OF WATER


Procedure:

Collect 250 ml of water avoiding contact with air add 2 ml of MnSO4 solution + 2ml of KI

stopper and shake thoroughly

add 20ml of H2SO4 withdraw 100ml and titrate against Na2S2O3 using

starch as indicator

If the volume of hypo is V ml the dissolved oxygen = 8

x V ppm

water technology 3

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