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Alkalinity Test in Water | Easy Titration Method

alkalinity test

Alkalinity Test in Water 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)

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 TCaustic Alkalinity
P = 00
P < 1/2 T0
P = 1/2 T0
P > 1/2 T2P – T
P = TT

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