Sodium Hydroxide

             NaOH                                          MW= 40

DEFINITION

Sodium hydroxide contains not less than 97.0 per cent and not more than the  equivalent of 100.5 per cent of total alkali, calculated as NaOH.

 

 CHARACTERS

White, crystalline masses, supplied as pellets, sticks or slabs, deliquescent,  readily absorbing carbon dioxide, very soluble in water, freely soluble in alcohol.

 

 IDENTIFICATION

A.    Dissolve 0.1 g in 10 ml of water R. Dilute 1 ml of the solution to 100 ml with  water R. The pH  of the final solution is not less than 11.0.

B.    2 ml of solution S (see Tests) gives reaction (a) of sodium.

 

 TESTS

Solution S

Carry out the procedure described below with caution. Dissolve 5.0 g in 12 ml of  distilled water R. Add 17 ml of hydrochloric acid R1, adjust to pH 7 with 1 M  hydrochloric acid  and dilute to 50 ml with distilled water R.

Appearance of solution

Dissolve 1.0 g in 10 ml of water R. The solution is clear and colourless .

 

 Carbonates

Not more than 2.0 per cent, calculated as Na2CO3, as determined in the assay.

 

 Chlorides: 

 Dissolve 1.0 g in 5 ml of water R, acidify the solution with about 4 ml of nitric acid R  and dilute to 15 ml with water R. The solution, without addition of dilute nitric acid R,  complies with the limit test for chlorides (50 ppm).

 

 Sulphates:

Dissolve 3.0 g in 6 ml of distilled water R, adjust to pH 7 with hydrochloric acid R  (about 7.5 ml) and dilute to 15 ml with distilled water R. The solution complies with  the limit test for sulphates (50 ppm).

 

 Iron:

10 ml of solution S complies with the limit test for iron (10 ppm).

 

 Heavy metals:

12 ml of solution S complies with limit test A for heavy metals (20 ppm). Prepare the  standard using lead standard solution (2 ppm Pb) R.

 

 ASSAY:

Dissolve 2.000 g in about 80 ml of carbon dioxide-free water R. Add 0.3 ml of  phenolphthalein solution R and titrate with 1 M hydrochloric acid . Add 0.3 ml of  methyl orange solution R and continue the titration with 1 M hydrochloric acid .

 

 1 ml of 1 M hydrochloric acid  used in the second part of the titration is equivalent to  0.1060 g of Na2CO3.

1 ml of 1 M hydrochloric acid  used in the combined titrations is equivalent to 40.00  mg of total alkali, calculated as NaOH.

Calculation

Result of later reaction:

STORAGE

Store in an airtight, non-metallic container.