P T SHUKUR, B Tech, MBA
Quantitative analysis for Quality Control of Water
Total Hardness
Total Hardness is estimated by complexometric titration with standard EDTA solution using Dotite BT as indicator
Procedure
Pipette out 50ml water sample into a conical flask. Add 10ml of buffer solution and wait for 5 minutes. Titrate with standard M/100 EDTA solution taken in the burette using Dotite BT as Indicator. End point is sharp color change from Wine red to blue. Total Hardness is calculated as follows.
Total Harness = V x 1000/50 mg/litre
Ca Hardness
Ca Hardness is estimated by complexometric titration with standard EDTA solution using Dotite NN as indicator.
Procedure
Pipette out 50ml water sample into a conical flask. Add 5ml of 10% KOH solution and wait for 5 minutes. Add 0.5ml NH2OH.HCl. Titrate with standard solution of M/100 EDTA taken in the burette using Dotite N’N’ Indicator. End point is sharp color change from Wine red to blue. Ca Hardness is calculated as follows.
Ca2+ = V x 0.4008 x 1000/50
In terms of Caco3 = Ca2+ x 2.495 mg/litre
Chloride in Water
Chloride content in water is estimated by Argentometric titration with standard AgNO3 using K2Cro4 as indicator.
Procedure
Pipette out 50 ml water sample into a clean conical flask. Add I ml of k2cro4 indicator solution into to the sample. Titrate with standard 0.1N agno3 solution. Endpoint is sharp color change to Orange red. Chloride ion is estimated as
Chloride (mg/l) = A x N x 35.45 x 1000 mg/litre
Vol. of sample
Where, A = Vol. of agno3 required for sample
N = Normality of agno3
Total Alkalinity
Total alkalinity in water sample can be determined by titrating a known volume of sample against standard sulphuric acid solution using methyl red indicator.
Procedure
Pipette out 50 ml water sample into a clean conical flask. Add 2-3 drops of methyl red indicator. Titrate with standard N/50 H2SO4 solution taken in the burette. Endpoint is sharp color change from blue to white. Alkalinity is calculated as
Total alkalinity = VX 1000/50 ppm
Total Dissolved Solids (TDS)
At present Conductivity/TDS meter is used to find the both parameters. The following chemical analysis can also be used.
1. Take 100ml of water into a pre-weighed clean, dry porcelain dish.
2. Evaporate the water in the basin to dryness over a water bath
3. Clean the outside of the dish, dry it in an air oven at 105oC for an hour to remove moisture, cool and weigh.
4. the difference between the weights is the weight of total soluble salts.
Calculation
Volume of water taken = 100ml
Weight of empty dish = Agrams
Weight of dish + residue = B grams
Weight of TDS in 100ml sample = (B – A) grams
TDS (mg/l) = (B – A) x 106
100
Total Suspended Solids
TSS in water sample is determined by filtering the sample through filters with nominal pore sizes varying from 0.45mm to about 2.0mm. TSS test is somewhat arbitrary because it depends on the pore size of the filter paper.
Procedure
Accurately weigh a GS 25 filter paper. Shake the given water sample vigorously and Filter 500ml sample through the filter paper using a filtration a pump. Dry at 100oC for 2 hr. Cool and weight is noted .TSS is calculated as
TSS = (W2-W1) /Vx 106 mg/litre
W1= Weight of filter paper
W2 = Weight of filter paper with sample
V= volume of sample taken
Total Phosphate in Circulating water
The estimation is based on the reaction of the phosphate ions with acidified molybdate reagent to give phosphor-molybdate complex which is then reduced to a blue compound by SnCl2 or by suitable reducing agent. The absorbance of the compound is measured by spectrophotometry.
Procedure
Pipette out 10 ml water sample into a clean graduated test tube. Add 1ml H2SO4 and 10 ml potassium per sulphate solution. Cover with aluminum foil, autoclave for 1 hr. Cool, add 2-3 drops phenolphthalein and add NaOH drop wise to pink colour. Add 5ml ammonium Molybdate solution. Mix well and add 0.25ml SnCl2. Make up to 50ml. Mix well and allow t stand 15mts. Measure absorption rate at 700nm using spectrophometer. Prepare a blank solution with distilled water and follow same procedure.
HCl Concentration (for acid washing of Chlorinator)
Before circulating the HCl in the hypo-chlorinator, its concentration will be analyzed. Concentration of HCl can be estimated by potentiometric titration using standard NaOH solution.
Procedure
Pipette out 10ml acid in to a 100ml beaker. Add 50ml Distilled Water and keep a magnetic stirrer in it. Dip pH meter electrode and slowly add standard NaOH (1N) from burette with stirring. When pH increases to 3 minimize addition of NaOH. Continue addition slowly with stirring till pH increases to 8. Note volume of NaOH. Then HCl percentage is calculated as
% HCl = (V1 x N1 x 0.3646)/sp. Gravity of HCl
Where V1 = Volume of NaOH
N1 = Normality of NaOH
Sp. Gravity is measured using a hydrometer
T Fe of water (Soluble Fe)
Total Iron in circulation water is estimated by absorption photometric method.
Procedure
Pipette out 50ml sample in to a conical flask. Add 5ml 3N HCl. Boil and reduce the volume to 25%. Cool and transfer in to a 50ml standard flask. Add 1ml NH2OH.HCl and 2.5ml O-phenanthrolein hydrochloride. Put a small piece of Congo red paper. Add 6N NH4OH drop by drop till color turns red. Add 2.5ml buffer solution and make up to volume 50ml. Wait for 30mts and take spectrophotometer reading at l = 510nm