Alkalinity test procedure:
Reagents:
- 0.01N HCl: Dilute 0.8ml of A. R. grade HCl in 1 litre of distilled water.
- Methyl Orange indicator: Dissolve 0.1 gms of Methyl Orange in distilled water and make up
the volume to 100 ml with distilled water. - Phenolphthalein indicator: Dissolve 1.0 gm Phenolphthalein powder in 100 ml ethanol.
Standardisation of 0.01 N HCL Solution :
Pipette out 10 ml of standard 0.01N sodium Hydroxide solution with a volumetric pipette in a 100ml conical flask. Add 4 drops of phenolphthalein indicator solution. Titrate against HCl solution taken in a burette. Titrate till the colour changes purple to colourless. This is the end-point.
CALCULATION:
N1V1 = N2V2 or, N1 = N2V2/N1
Where,
N1= Normality of HCl
V1 = Volume of HCl(Burette reading)
N2 = Normality of sodium Hydroxide (previously standardised)
V2 = Volume of sodium Hydroxide (10 ml)
Read Also: List of Laboratory Apparatus and their Uses
Determination of Total Alkalinity in Water:
Pipette out 10 ml of water sample in 100 ml conical flask. Add 1 drop of Methyl Orange indicator in sample and titrate against standard 0.01N HCl solution. Titrate till colour changes from yellow to orange. Note this burette reading (as B. R.)
CALCULATION:
Total Alkalinity in ppm = {B. R. x Normality (HCl) x 50 x 1000}/10 ppm
Determination of Phenolphthalein Alkalinity in Water:
10 ml of water sample in 100 ml conical flask. Add 4 drops of Phenolphthalein indicator in sample and titrate against standard 0.01N HClsolution. Titrate till colour changes from purple to colourless. Note this burette reading (as B. R.)
CALCULATION:
Phenolphthalein Alkalinity in ppm = {B. R. x Normality (HCl) x 50 x 1000}/10 ppm
Determination of Caustic Alkalinity in Water :
Determine total alkalinity (T) and phenolphthalein alkalinity (P) and calculate caustic alkalinity.
CALCULATION:
| Value of P and T | Caustic Alkalinity |
| P = 0 | 0 |
| P < 1/2 T | 0 |
| P = 1/2 T | 0 |
| P > 1/2 T | 2P – T |
| P = T | T |
