Verification of sulfite with formaldehyde

Chemicals needed

distilled water

formaldehyde solution 1% GSGESUND.gif (476 Byte) Xn    R 40-43    S 23-37

sodium sulphite GSGESUND.gif (476 Byte) Xi    R 31

phenolphtalein solution

hydrochloric acid 7%

it is basically advantageous to use still less concentrated acids

Equipment needed

test tube

Test procedure


The diluted solution can be disposed of into the drainage.


Sodium hydroxymethyl sulfite(bisulfite adduct) and sodium hydroxide are formed. The latter is strongly alkaline and therefore causes the indicator to change.

HCHO + H2O +  Na2SO3 --> HOCH2OSOO- + 2 Na+ + OH-


Dropwise added formaldehyde solution causes the indicator to change.


Derived from experiment 6.,"Nachweis mit Formaldehyd", p.122,[7]