e and barium bromide weighing
0.6 gram is treated with 45.15 cubic centimeters of 0.2017 N silver
nitrate, and the excess titrated with 25 cc. of 0.1 N KSCN solution,
using ferric alum as an indicator. Calculate the percentage of bromine
in the sample.

!Answer!: 40.11%.

72. A mixture of the chlorides of sodium and potassium from 0.5000
gram of a feldspar weighs 0.1500 gram, and after solution in water
requires 22.71 cc. of 0.1012 N silver nitrate for the precipitation of
the chloride ions. What are the percentages of Na_{2}O and K_{2}O in
the feldspar?

!Answer!: 8.24% Na_{2}O; 9.14% K_{2}O.

GRAVIMETRIC ANALYSIS

73. Calculate (a) the grams of silver in one gram of silver chloride;
(b) the grams of carbon dioxide liberated by the addition of an excess
of acid to one gram of calcium carbonate; (c) the grams of MgCl_{2}
necessary to precipitate 1 gram of MgNH_{4}PO_{4}.

!Answers!: (a) 0.7526; (b) 0.4397; (c) 0.6940.

74. Calculate the chemical factor for (a) Sn in SnO_{2}; (b) MgO
in Mg_{2}P_{2}O_{7}; (c) P_{2}O_{5} in Mg_{2}P_{2}O_{7}; (d) Fe in
Fe_{2}O_{3}; (e) SO_{4} in BaSO_{4}.

!Answers!: (a) 0.7879; (b) 0.3620; (c) 0.6378; (d) 0.6990; (e) 0.4115.

75. Calculate the log factor for (a) Pb in PbCrO_{4}; (b) Cr_{2}O_{3}
in PbCrO_{4}; (c) Pb in PbO_{2} and (d) CaO in CaC_{2}O_{4}.

!Answers!: (a) 9.8069-10, (b) 9.3713-10; (c) 9.9376-10; (d) 9.6415-10.

76. How many grams of Mn_{3}O_{4} can be obtained from 1 gram of
MnO_{2}?

!Answer!: 0.8774 gram.

77. If a sample of silver coin weighing 0.2500 gram gives a
precipitate of AgCl weighing 0.2991 gram, what weight of AgI could
have been obtained from the same weight of sample, and what is the
percentage of silver in the coin?

!Answers!: 0.4898 gr.; 90.05%.

78. How many cubic centimeters of hydrochloric acid (sp. gr. 1.13
containing 25.75% HCl by weight) are required to exactly neutralize
25 cc. of ammonium hydroxide (sp. gr. .90 containing 28.33% NH_{3} by
weight)?

!Answer!: 47.03 cc.

79. How many cubic centimeters of ammonium hydroxide solution (sp. gr.
0.96 containing 9.91% NH_{3} by weight) are required to precipitate
the aluminium as aluminium hydroxide from a two-gram sample of alum
(KAl(SO_{4})_{2}.12H_{2}O)? What will be the weight of the ignited
precipitate?

!Answers!: 2.26 cc.; 0.2154 gram.

80. What volume of nitric acid (sp. gr. 1.05 containing 9.0%
HNO_{3} by weight) is required to oxidize the iron in one gram of
FeSO_{4}.