Acidity in Water
Reagent
1. Sodium Hydroxide solution -15 N
a. Sodium Hydroxide solution – 1 N:- Dilute 67ml of 15 N NaOH to 1 liter with Distilled water.
b. Sodium Hydroxide solution – 0.02 N:- Dilute 20ml of 1 N NaOH to 1 liter with Distilled water and standardize using std potassium acid phthalate (KHP).
a. Sodium Hydroxide solution – 1 N:- Dilute 67ml of 15 N NaOH to 1 liter with Distilled water.
b. Sodium Hydroxide solution – 0.02 N:- Dilute 20ml of 1 N NaOH to 1 liter with Distilled water and standardize using std potassium acid phthalate (KHP).
2. Potassium Acid Phthalate – 0.02 N – Dissolve 4.084 g of potassium acid phthalate ( dried at 120oC for 2 hours ) in carbon dioxide-free Distilled water and dilute to 1 liter.
3. Phenolphthalein indicator – Dissolve 0.5 g of Phenolphthaleinin 100 ml (1:1) (v/v) alcohol-water mixture and add 0.02 N NaOH dropwise till very faint pink color is observed.
4. Methyl Orange indicator – Dissolve 0.5g methyl orange in distilled water and makeup to 100 ml in a volumetric flask.
PROCEDURE
- pipette out 20ml of sample in 100 ml beaker
- check pH of Sample
- if pH is less than 3.7, Add 2 drops of methyl orange indicator and titrate with 0.02N NaOH solution until the color change to faint orange of pH 3.7. Record the volume of NaOH used.
- if pH is more than 3.7, Add 2-3 drops of phenolphthalein indicator and titrate against 0.02N NaOH to the appearance of the faint pink color characteristic of pH 8.3. Record the volume of NaOH used.
Calculation
Acidity (pH – 3.7) =A*N*50000/V
Acidity (pH – 8.3) =B*N*50000/V
where,
A= used volume in ml of std NaOH titrate to pH 3.7
B= used volume in ml of std NaOH titrate to pH 3.7
N= Normality of std NaOH
V= volume in ml of the sample taken for the test
REFERENCE SPECIFICATION: IS 3025 Part-22