Sodium Hydroxide
Caustic Soda
NaOH
Sodium
Mol. Wt. 40.00
hydroxide
Definition
〔1310-73-2〕
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
(2)
(1)
Sodium Hydroxide solution (1 → 50) is strongly alkaline.
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).
the consumed volume of 1 mol/l hydrochloric acid as b (ml).
Content of sodium hydroxide (NaOH)
=
0.04000 × b × 40
× 100 (%)
Weight (g ) of the sample
Content of sodium carbonate (Na2CO3)
Express
=
0.05299 × (a − b) × 40
× 100 (%)
Weight (g ) of the sample