Sodium Hydroxide
Caustic Soda NaOH
Sodium Hydroxide Caustic Soda NaOH Mol. Wt. 40.00 Sodium
hydroxide 〔1310-73-2〕 Definition Sodium Hydroxide occurs as two forms: the
crystal form called Sodium Hydroxide (crystal) and anhydrous form called Sodium
Hydroxide (anhydrous). Sodium Hydroxide (crystal) is a mixture of sodium
hydroxide (NaOH) and sodium hydroxide monohydrate (NaOH･H2O). Content Sodium
Hydroxide (crystal) contains 70.0－75.0% of sodium hydroxide (NaOH). Sodium
Hydroxide (anhydrous) contains not less than 95.0% of sodium hydroxide (NaOH).
Description Sodium Hydroxide (crystal) occurs as white crystalline powder or
granules. Sodium Hydroxide (anhydrous) occurs as white lumps having various
shapes including pellets, flakes, and rods, or as a white powder.
Identification (1) Sodium Hydroxide solution (1 → 50) is strongly alkaline. (2)
Sodium Hydroxide responds to all tests or Sodium Salt as described in the
Qualitative Tests. Purity (1) Clarity and color of solution Colorless, almost
clear. Sample Solution Weigh 50 g of Sodium Hydroxide, and dissolve in freshly
boiled and cooled water to make 250 ml. Test Solution Measure 5 ml of the
sample solution, and mix with 20 ml of water. (2) Sodium carbonate The content
of sodium carbonate (Na2CO3) obtained in the Assay is not more than 2.0%. (3) Heavy
metals Not more than 30 µg/g as Pb. Test Solution Measure exactly 5 ml of the
sample solution prepared in (1) above, neutralize by gradually adding diluted
hydrochloric acid (1 → 4), and add 2 ml of diluted acetic acid (1 → 20) and
water to make 50 ml. Control Solution To 3.0 ml of Lead Standard Solution, add
2 ml of diluted acetic acid (1 → 20) and water to make 50 ml. (4) Mercury Not
more than 0.10 µg/g as Hg. Test Solution Measure 10 ml of the sample solution
prepared in test (1) above, add 1 ml of potassium permanganate solution (3 →
50) and about 30 ml of water, and shake. Neutralize by gradually adding
purified hydrochloric acid, add 5 ml of diluted sulfuric acid (1 → 2), and
cool. Procedure Add hydroxylamine hydrochloride solution (1 → 5) until the
purple color of the potassium permanganate in the test solution disappears and
the precipitate of manganese dioxide dissolves, add water to make 100 ml, and
transfer into a gas washing bottle for the atomic absorption spectrophotometer.
Add 10 ml of stannous chloride TS, immediately connect with the atomic
absorption spectrophotometer, and start the diaphragm pump to circulate the
air. When the reading on the recorder increase rapidly and then indicates a
constant value, measure the absorbance. The absorbance is not more than that of
the following solution: Measure 2.0 ml of Mercury Standard Solution, add 1 ml
of potassium permanganate solution (3 → 50), 30 ml of water, and the same
amount of purified hydrochloric acid as that used for preparing the test solution,
and proceed in the same manner as for the test solution. (5) Arsenic Not more
than 4.0 µg/g as As2O3. Test Solution Measure 2.5 ml of the sample solution
prepared in test (1) above, add 5 ml of water, and neutralize by gradually
adding hydrochloric acid. Apparatus Apparatus B. Assay Weigh accurately about
50 g of Sodium Hydroxide, and add freshly boiled and cooled water to make
exactly 1,000 ml. Use this solution as the sample solution. Measure exactly 25
ml of the sample solution, add 10 ml of freshly boiled and cooled water, and
titrate with 1 mol/l hydrochloric acid (indicator: 1 ml of bromophenol blue
TS). After neutralizing, add about 1 ml of 1 mol/l hydrochloric acid, boil for
about 5 minutes, and cool. Titrate the excess acid with 0.1 mol/l sodium
hydroxide, and determine the volume (a ml) of consumed 1 mol/l hydrochloric
acid. Separately, measure exactly 25 ml of the sample solution, transfer into a
flask with a ground-glass stopper, and add 25 ml of freshly boiled and cooled
water. To the solution, add 10 ml of barium chloride solution (3 → 25),
stopper, shake gently, and titrate with 1 mol/l hydrochloric acid (indicator: 1
ml of phenolphthalein TS). Express the consumed volume of 1 mol/l hydrochloric
acid as b (ml). Content of sodium hydroxide (NaOH) 100(%) Weight(g) of the
sample 0.04000 b 40 × × × = Content of sodium carbonate (Na2CO3) 100(%)
Weight(g) of the sample 0.05299 (a b) 40 × × − × =
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