{2}SO_{4} by weight) will be required to displace the
chloride in the calcium chloride formed by the action of 100 cc. of
0.1072 N hydrochloric acid on an excess of calcium carbonate, and how
many grams of CaSO_{4} will be formed?

!Answers!: 0.298 cc.; 0.7300 gram.

36. Potassium hydroxide which has been exposed to the air is found on
analysis to contain 7.62% water, 2.38% K_{2}CO_{3}. and 90% KOH. What
weight of residue will be obtained if one gram of this sample is added
to 46 cc. of normal hydrochloric acid and the resulting solution,
after exact neutralization with 1.070 N potassium hydroxide solution,
is evaporated to dryness?

!Answer!: 3.47 grams.

37. A chemist received four different solutions, with the statement
that they contained either pure NaOH; pure Na_{2}CO_{3}; pure
NaHCO_{3}, or mixtures of these substances. From the following data
identify them:

Sample I. On adding phenolphthalein to a solution of the substance, it
gave no color to the solution.

Sample II. On titrating with standard acid, it required 15.26 cc. for
a change in color, using phenolphthalein, and 17.90 cc. additional,
using methyl orange as an indicator.

Sample III. The sample was titrated with hydrochloric acid until the
pink of phenolphthalein disappeared, and on the addition of methyl
orange the solution was colored pink.

Sample IV. On titrating with hydrochloric acid, using phenolphthalein,
15.00 cc. were required. A new sample of the same weight required
exactly 30 cc. of the same acid for neutralization, using methyl
orange.

!Answers!: (a) NaHCO_{3}; (b) NaHCO_{3}+Na_{2}CO_{3}; (c)NaOH; (d)
Na_{2}CO_{3}.

38. In the analysis of a sample of KHC_{4}H_{4}O_{6} the following
data are obtained: Weight sample = 0.4732 gram. NaOH solution used =
24.97 cc. 3.00 cc. NaOH = 1 cc. of H_{3}PO_{4} solution of which 1
cc. will precipitate 0.01227 gram of magnesium as MgNH_{4}PO_{4}.
Calculate the percentage of KHC_{4}H_{4}O_{6}.

!Answer!: 88.67%.

39. A one-gram sample of sodium hydroxide which has been exposed to
the air for some time, is dissolved in water and diluted to exactly
500 cc. One hundred cubic centimeters of the solution, when titrated
with 0.1062 N hydrochloric acid, using methyl orange as an indicator,
requires 38.60 cc. for complete neutralization. Barium chloride in
excess is added to a second portion of 100 cc. of the solution, which
is diluted to exactly 250 cc., allowed to stand and filtered. Two
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