WATER ANALYSIS
Water Quality parameters
The presence of dissolved salts (both organic andinorganic) contaminate water. The purity or quality of water can be assessed by determining the quantity of various salts or gases present in it. The following are Mater quality parameters which are measured by chemicalanalysis.
1.pH
plH is the measure of acidity or alkalinity of water. Non polluted (pure) wvater has pH value equai to 7.
pH=7 Neutral
pH <7 Acidic
pH>7 Alkaline
Water of pH less than 4 will produce sour taste. pH below 6.5 allows corrosion in pipes thereby discharging toxic metals such as Zn, Po, Cd and Cu. High pH causes formation of trihalomethanes which have toxic effects.
Determination of pH of water
1) Calibrate the pH meter with two standard buffer solutions of pH9.2 and 4.
2) Dissolve 10.2 g ofpot. hydrogen phthalate in distrilled water and dilute it to one litre. It provides the solution with pH =4 at room
temperature.
3) Dissolve 3.81 g ofNa,B,0,. 10H,0 in distilled water and dilute it to one litre. It provides to solution witih pH=9.2 at roorntemperature.
4. Rinse the electrode thoroughly with distilled water and wipe out the water using a tissue paper.
5. Dip the electrode in the sample water. Swril the solution and wait for l minute for steady reading.
2. Acidity
Acidity of water is due to the presence of mineral acids and hydrolysis of some salts (e.g. NH,CI, CuSO,).
Determination of Acidity of water
Acidity is determined by titrating the water sample against a strong alkali like NaOH using phenolphthalein or methyl orange as indicator.
Method
1) Take 100 ml of colourless sample of water in a conical flask. Now, add 3 to 4 drops of methyl orange indicator.
2) The solution turns pink. Titrate the solution against NaOH till the colour changes from pink to yellow.
3) Now, add a few drops of phenolphthalein indicator to the same solution and titrate further with NaOH until the solution turns pink.
Calculation
1000 ml of NaOH= 50 gms of CaCO,
i) Methyl orange acidity
mg/L as CaCO, = A× N×1000 × 50/(Volume of sample)
ii) Phenolphthalein acidity
mg/L as CaCO, = B× N× 1000×50/(Volume of sample)
iii) Total acidiiy
mg/L as CaCO, = (A+B) N × 1000 ×50 / (Volume of sample)
Here,
A=Volume of NaOH consumed when methyl orange indicator is used
B=Volume of NaOH consumed when phenolphthalein indicator is used
3. Alkalinity
Alkalinity ofwater is due to the presence of free hydroxyl ions and hydroxyl ions formed, by. the hydrolysis of 'some salts (e.g. carbonates and bicarbonates). Alkalinity is also due to the dissolution of CO, in water. Salts such as silicates, phosphates and borates also produce alkalinity.
Determination of Alkalinity of water
Alkalinity is determined by titrating the water Sample against a strong acid like HCI or H2SO4 using methyl orangẻ or phenolphthalein as indicator.
Method
1. Take 100 ml of colourless water sample in a conical flask. Now, add 3 to 4 drops of phenolphthalin indicator.
2) The solution tuns pink. Titrate the solution against 0.1 N HCI till pink colour disappears.
3) Now, add 3 to 4 drops of methyl orange indicator to the same solution and continue the titration until the yellow colour of the
solution turns pink.
Calculation
1000 ml of IN HCl = 50 gms of CaCO,
i) Phenolphthalein alkalinity
mg/L as CaCO, = A × N × I000 × 50/{Volume of sample}
ii) Methyl orange alkalinity
mg/L as CaCO, = B×N×1000× 50/ (Volume of sample)
ii) Total alkalinity
mg/L as CaCO, = (A+B) × N×1000 × 50/
(Volume of sample)
Here, A = Volume of HCl conserned when phenolphthalein indicator is used
B= Volume ofHCl consumed when methyl orange indicator is used