Magnesium Oxide
MgO
Mol. Wt. 40.30
magnesium oxide
Content
〔1309-48-4〕
Magnesium Oxide, when ignited, contains not less than 96.0% of
magnesium oxide (MgO).
Description
Magnesium Oxide occurs as a white or whitish powder, or granule.
Identification
Dissolve 1 g of Magnesium Oxide in 25 ml of diluted hydrochloric
acid (1 → 4). The solution responds to the test for Magnesium Salt as described in the
Qualitative Tests.
Purity (1)
Water-soluble substances Not more than 2.0%.
Weigh 2.0 g of Magnesium Oxide, add 100 ml of water, heat in a water bath for 5
minutes, and immediately filter. Cool, measure 25 ml of the filtrate, evaporate to
dryness in a water bath, and dry at 105℃ for 1 hour. Weigh the residue.
(2)
Hydrochloric acid-insoluble substances Not more than 1.0%.
Weigh 2.0 g of Magnesium Oxide, and add 75 ml of water. Add dropwise
hydrochloric acid to the suspension while shaking until the insoluble substances no
longer reduce, and boil for 5 minutes. Cool, filter through a filter paper for quantitative
analysis (5C), wash the residue on the filter paper thoroughly with water until the
washings do not give positive tests for Chloride, and ignite together with the filter paper.
Weigh the residue.
(3)
Free alkali
Measure 50 ml of the filtrate obtained in test (1), add 2 drops of
methyl red TS, and add 2.0 ml of 0.05mol/l sulfuric acid. A red color develops.
(4)
Heavy metals Not more than 20 µg/g as Pb.
Test Solution Weigh 1.0 g of Magnesium Oxide, and dissolve in 25 ml of diluted
hydrochloric acid (1 → 4). Evaporate to dryness in a water bath, and near the end of
evaporation, stir the residue well to make a fine powder. Dissolve with 20 ml of water,
evaporate to dryness in the same manner, and dissolve again with 20 ml of water. Filter
if necessary. Add 2 ml of diluted acetic acid (1 → 20) and water to make 50 ml.
Control Solution Measure exactly 2 ml of Lead Standard Solution, add 2 ml of
diluted acetic acid (1 → 20) and water to make 50 ml.
(5)
Calcium oxide
Not more than 1.5%.
Measure exactly 50 ml of solution A prepared in Assay below, and add water to
make 300 ml. Add 0.6 ml of tartaric acid (1 → 5), then 10 ml of triethanol amine (3 →
10) and 10 ml of potassium hydroxide solution (1 → 2). Allow to stand for 5 minutes,
titrate with 0.01 mol/l EDTA, using a microburet (indicator: about 0.1 g of NN indicator),
and express the consumed volume as b ml. The end point is observed when the
red-purple color of the solution completely disappears and the solution becomes blue.
Calculate the content by the formula
Content of calcium oxide (CaO) =
(6)
Arsenic
b (ml) × 0.5608
(%) .
Weight (g) of the sample
Not more than 4.0 µg/g as As2O3.
Test Solution Weigh 0.50 g of Magnesium Oxide, and dissolve in 5 ml of diluted
hydrochloric acid (1 → 4).
Apparatus Apparatus B.
Loss on Ignition Not more than 10.0% (1,000℃, 30 minutes).
Assay
Weigh accurately about 0.5 g of Magnesium Oxide, previously ignited,
moisten with 5 ml of water, add 10 ml of hydrochloric acid and 10 ml of perchloric acid,
cover with a watch glass, and heat gradually. After thick white fumes are evolved, heat
for another 10 minutes. After cooling, add about 50 ml of hot water and 5 ml of diluted
hydrochloric acid (1 → 2), heat slightly, and immediately filter through a filter paper
for quantitative analysis (5C), and add water to the filtrate to make exactly 500 ml.
Take this solution as solution A. Measure exactly 10 ml of solution A, add water to make
100 ml, add 5 ml of ammonia−ammonium chloride buffer (pH 10.7) and 2 drops of
eriochrome black T TS, and immediately titrate with 0.01 mol/l EDTA until the red color
of the solution changes to blue. Determine the consumed volume as a ml. Using b ml of
the consumed volume obtained under Purity (5), calculate the content by the formula
Content of magnesium oxide ( MgO) =
(a − 0.2b) × 2.0152
(%) .
Weight (g ) of the sample