Determination Purity of Formaldehyde by Titration | Formaldehyde Purity

The provided this procedure, to determine the purity of formaldehyde using a back-titration method with sodium hydroxide (NaOH) and hydrochloric acid (HCl).

APPARATUS

a). 250 ml Erlenmeyer flask.

b). 5 ml stoppered weighing bottle.

c). 100 ml measuring cylinder.

d). Burette.

REAGENTS

a). 1 (M) sodium sulfite solution.

b). 1.0 (N) standard hydrochloric acid (HCl).

c). Phenolphthalein indicator solution.

Purity of Formaldehyde Procedure 

Take formaldehyde sample in a beaker and neutralize with 1(N) NaOH solution using phenolphthalein indicator. 

Take 50 ml of 1 (M) sodium sulphite solution in a 250-ml Erlenmeyer flask. 

Add 3 drops of phenolphthalein indicator and carefully neutralize by titration with 1.0(N) HCl solution till it becomes colorless. 

Now take a neutral formaldehyde sample in a 5 ml stoppered weighing bottle. 

From it transfer about 2 gm(accurately weighed) sample to the Erlenmeyer flask. 

Put the stopper and shake properly for thorough mixing. 

Titrate the resulting mixture slowly with standard 1.0 (N) HCl acid taken in a burette till complete deceleration.

1 ml 1(N) HCl acid = 0.03003 gm HCHO

Purity of formaldehyde (%) = Acid Titrate (ml) x normality of acid x 3.003/W

Wt of formaldehyde sample taken (gm)

Formaldehyde purity = 37- 40%