Analysis of purified water
Determination of pH
Reference:
BP, 1988 p A-103
Equipment
: pH meter
Reagents
: standard buffer solutions (pH 4.0, 7.0, 9.2)
buffer solutions of pH closer to the expected pH value of the sample at
25 ° ± 2°C. Immerse the
electrode in water. Shake it for about one minute and note the constant reading
of pH on the pH meter.
Determination of total solids
Reference: IS: 3025-1964 P18
Procedure : Note
the tare weight of the Evaporating dish. Evaporate 100ml of the sample in the
evaporating dish on steam bath. Dry the residue at 105°C for one hour. Col in a desicator and weigh. Not the weight of
the residue.
Total
solids = Weight of residue (mg.) ´ 1000
(ppm) Volume
of sample taken (ml.)
Determination of total dissolved solids
Reference: IS: 3025-1964 p 19
Procedure: Filter
the sample through what man filter paper 42. Not the tare weight for the
evaporating dish. Evaporate 100ml of the filtered sample in the evaporating
dish on steam bath. Dry the residue at 105°C
for one hour. Cool in a desicator and weigh. Note the weight of the residue.
Total
dissolved Solids = Wt. Of residue
(mg.) ´ 1000
(ppm)
Volume of sample taken (ml.)
Determination of total hardness
Reference: Chemical & Biological methods for
water pollutions studies p-73
Reagents
BDH
Total hardness indicator tablets
0.01
M EDTA Solutions
Dissolve
3.723 g of disodium salt of EDTA in water to prepare 1 Liter of solution
In a volumetric flask.
Buffer Solutions
a) Dissolve 16.9 g of NH4CL in 143 ml. Of conc.
Ammonia (25%)
b) Dissolve
1.179 g of disodium EDTA and 0.78 g of MgSO4. 7H2O in
60ml. Of water.
Mix
both (a) and (b) solutions and dilute to 250ml. With water.
Procedure
Take 100ml of sample in conical flask. (If sample is
having higher calcium, take a smaller volume and dilute to 50ml.).
Add 1ml. Buffer and one tablet of BDH total hardness
indicator. The solution turns wine red. Titrate against EDTA solution. At
the end point, Colour changes from wine red to blue.
Calculations
Total hardness (as CaCO3) = Vol. Of 0.01
M EDTA used ´ 1000
(ppm)
Vol. Of sample taken
Determination of content of
chloride.
Reference: IS: 3025-1964 p 34
Reagents
0.02
N Silver Nitrate
Dissolve
3.400 g of dried AgNO3 (AR) in water to make 1 litre of
solutions in a volumetric flask. Keep this solution in a amber coloured bottle.
Potassium
Chromate solution (5%)
Dissolve
5g of potassium Chromate in water and make up to 100ml. Add silver nitrate
solution to produce slight red precipitate and filter. Keep the filtrate as
indicator in a bottle.
Procedure
Take
100ml. of sample in a conical flask and add 2ml. of potassium Chromate
indicator solution. Titrate with 0.02N Silver Nitrate until a persistent red
tinge appears. Note the volume of silver nitrate used.
Calculations
Chloride
= V ´ N ´ 1000 ´ 35.5
(ppm)
100
Where:
V= Volume of AgNO3 Used (ml.)
N = Normality of AgNO3
Determination of Sulphate
Reference: IS : 3025-1964 P-27
Regents
1
N Nitric Acid
BDH
Total hardness tablet
Standard Barium Chloride Solution
Dissolve
2.443 g of barium Chloride in water and dilute to 1 litre in a volumetric
flask.
Buffer Solution
Dissolve
67.5 g of ammonium Hydroxide (Sp. gr. 0.92) and dilute with water to 1 litre.
Standard
EDTA Solution (0.01M)
Dissolve
3.723 g of disodium salt of EDTA in water to make up to 1000 ml in a volumetric
flask.
Procedure
Neutralize
125 ml of the sample with dilute nitric acid (1N) adding a slight excess and
boil to expel carbon dioxide. Add 10 ml or more if required, of standard barium
Chloride solution to the boiling solutions and allow to cool. Dilute to 250 ml,
makes and allow the precipitates to settle. Withdraw 50 ml of the clear
solution; add 0.5 to 1.0 ml of buffer and one tablet of BDH total hardness
indicator. Titrate with standard EDTA solution to a blue colour which does not
change on addition of further drops of EDTA solutions.
Calculation
Sulphate
(as SO4) = 9.6 (0.1 A+B-4C)
(ppm)
Where:
A
= Total hardness of the sample*
B
= Volume of standard barium chloride taken (ml)
C
= Volume of standard EDTA used (ml)
*Total
hardness (A)
Procedure
Take
100 ml of sample in a conical flask (if sample has higher Concentration
of Calcium, then take 25 ml of sample and dilute to100 ml) add 1 ml
of buffer solution and one tablet of BDH total hardness indicator or erichrome
Black T. Titrate with standard 0.01 M EDTA solution till the colour changes
from wine red to blue .
Calculations
Totalhardness (as CaCO3) = Volume of EDTA used ´ 1000
(mg /
litre) Volume
of sample taken
Determination of Calcium
Reference: Manual on water and waste water
analysis P,88
Reagents
0.01 M
EDTA solutions
Dissolve
3.723 g of disodium salt EDTA in water to prepare 1 litre of solution in a
volumetric flask.
2 N Sodium hydroxide
Dissolve
80.0 g of NaOH in 1000 ml in a Volumetric flask.
Muroxide
indicator or Ammonium Perpurate
Mix 0.1 gm Murexide with 10.0 gm of NaCL and grind it in pastle mortar.
Take
50 ml of sample in conical flask and add 1 ml of sodium hydroxide to raise pH
to 12.0. Add a pinch of murexide or ammonium perpurate
indicator. Titrate with 0.01 M EDTA till pink colour changes to
purple. Note the volume of EDTA required and keep it aside to compare end
points of sample titrated.
Calculation
Calcium = Vol. Of 0.01 M EDTA used ´ 400.8
(ppm) Vol.
Of sample taken
Determination of content of CO2
Reference: IP 1985 p 544
Regents
0.15%
W/V Calcium Hydroxide solution in water.
Take
25 ml of sample and add 25 ml of Calcium Hydroxide solutions. Find out if any
turbidity is in the solutions. Absence of turbidity indicates that the carbon
dioxide is not present.
Determination of Oxidisable substance
Reference: Analar standard of chemicals p-870
Reagents
0.01 N Potassium permanganate solution
Dilute sulphuric acid. (Appx.10%)
Procedure
Take 500 ml of sample in conical flask and add 1 ml of dilute sulphuric acid. Add 0.5 ml of 0.01 N Potassium Permanganate and heat to boiling. The pink colour does not entirely disappear.
Determination of content of Ammonia.
Reference: IP- 1985 p.544
Reagents
Dilute Ammonium Chloride solution.
Alkaline Potassium Mercury-Iodide solutions(Nessler’s Regent)
Take 3.5 g of Potassium Iodide and 1.25 g of Mercuric Chloride in a 100 ml of Volumetric Flask. Dissolve in 80 ml of water. Add a cold saturated Solution of Mercuric Chloride in flask with constant stirring until a slight red precipitate remains. Dissolve 12 g of Sodium Hydroxide in the above solution and add a little more of cold saturated solution of Mercuric Chloride and sufficient water to produce 100 ml. Allow to stand and decant the clear liquid.
Procedure
Take 20 ml of sample in Nessler Cylinder (1) and add 1 ml of alkaline Potassium Mercuric- Iodide solution and observe the solution against While tile. Take 7.5 ml
of sample. Add 2.5 ml of Dil. Ammonium chloride and 1.0 ml of Nessler’ reagent.
NESSLER CYLINDER (1) NESSLER CYLINDER(2)
Colour of solution (1) should be less intense as compared to (2)
Determination of Acidity or Alkalinity
Reference: Chemical & Biological methods for water pollution studies
ACIDITY:
Reagents
0.05N NaOH
Phenolphthalein
Methyl Orange
Procedure
Take 100 ml of sample in a titration flask. Add 2-3 ml of methyl orange indicator.
1. If soln. turns yellow, Methyl orange acidity absent. In case contents turn pink, titrate with 0.05N Sodium hydroxide.
End point : Pink to yellow
2. Now add phenolphthalein. Titrate with 0.05N Sodium hydroxide.
CALCULATIONS:
(METHYL ORANGE ACIDITY)
(mg/litre) (A) = VXN X 1000 X 50
vol. of sample
(PHENOLPHATHALEIN ACIDITY)
(mg/litre) (B) = VXN X 1000 X 50
vol. of sample
Total Acidity: (A+B) X N X 1000 X 50
vol. of sample
ALKALINITY:
Reagents
0.1N HCl
Phenolphthalein
Methyl Orange
Procedure
Take 100 ml of sample in a titration flask. Add 2-3 ml of phenolphthalein indicator.
1. Carbonate Alkalinity(CO3)
CALCULATIONS:
(PHENOLPHTHALEIN ALKALINITY) ———P
(mg/litre) (PA) = VXN X 1000 X 50
vol. of sample
2. Bicarbonate Alkalinity(HCO3)
CALCULATIONS:
(METHYL ORANGE ALKALINITY) ———M
(mg/litre) (TA) = VXN X 1000 X 50
vol. of sample
|
IF |
CO3 Alkalinity |
HCO3 Alkalinity |
|
|
|
|
|
|
|
|
|
P = 0 |
0 |
T |
|
|
|
P < ½ T |
2P |
T-2P |
|
|
|
P= ½ T |
2P |
0 |
|
|
|
P> ½ T |
2(T-P) |
0 |
|
|
|
P=T |
0 |
0 |
|
|
|
|
|
|
|
|
Determination of Chemical Oxygen (COD).
Reference: IS: 2488-1966
Reagents
Conc. Sulphuric acid
Mercuric Sulphate
Silver Sulphate
0.25 N Potassium Dichromate
Dissolve 12.259 gm of Potassium Dichromate Previously dried at 1100 C for one hour
in water to make 1 litre of solution.
Ferroin Indicator
Dissolve 1.485 gm of 1.10 phenanthroline and 0.695 gm of ferrous sulphate in water to make 100 of solution.
0.1 N Ferrous ammonium sulphate (FAS solution)
Dissolve 39.2 gm of ferrous ammonium sulphate in water adding 20 ml of conc. H2SO4
To make 100 ml of solution. Standardise the solution as follows:-
Weigh accurately about 150 mg of potassium dichromate (AR grade) previously dried at 1100 C for one hour. Dissolve in about 20 ml water and add 10 ml of conc. Sulphuric acid. Cool, add few drops of ferroin indicator and titrate with ferrous ammonium sulphate solution.
Normality = Wt. Of K2Cr2O7 (mg)
Vol. Of FAS used X 49.03
Procedure
Take 20 ml of sample in a 250-500 ml COD flask. Add to it, 20 ml of 0.25 N K2Cr2O7 solution and a pinch of silver sulphate and mercuric sulphate. Add 40 ml conc. Sulphuric acid and a few glass beads to avoid bumping. Fix a Friedrich condenser o the neck of the flask and reflux it for 2 hours on a hot plate. Wash the condenser with about 100 ml of distilled water. Cool to room temperature. Add few drops of Ferroin indicator and titrate with 0.1 N ferrous ammonium sulphate. Similarly, run a blank with distilled water same quantity of the chemicals.
Calculation
COD (ppm) = (b-a) x N x 1000 x 8
V
Where :
a = Vol. Of ferrous ammonium sulphate used with sample
b = Volume of ferrous ammonium sulphate used with blank
V = Volume of sample ammonium sulphate used.
N = Normality of ferrous ammonium sulphate used.
NOTE :
Dilute and volume of sample to be taken can be adjusted depending upon its expected COD value which can be judged from the solution before reflux.
Analysis of purified water PDF Notes
