Problems B
183
the reaction of concentrated H 2 SO 4 with nitrates in the presence of metallic
mercury, by the reaction
2KN0 3 + 4H 2 SO 4 + 3Hg -> K 2 SO 4 + 3HgSO 4 + 4H 2 O + 2NO
In a simple form of this apparatus, the NO is collected over water in a graduated tube and its volume, temperature, and pressure are measured. A 1.000 g
sample containing a mixture of KNO 3 and K 2 SO 4 is treated in this manner,
and 37.50 ml of NO is collected over water at a temperature of 23°C and a
pressure of 732.0 torr. Calculate the percentage of KNO 3 in the original sample.
20. A commercial laboratory wished to speed up its routine analysis for HNO 3 in
a mixture of acids, using the nitrometer mentioned in Problem 19. To do this, it
collects the NO over mercury, uses enough concentrated H 2 SO 4 to make
correction for water vapor unnecessary, thermostats its graduated tube at
25.0°C, and takes all pressure measurements at 730.0 torr. The tube is graduated to 100.0 ml. What weight of original acid sample should always be taken
so that the buret reading under these conditions also indicates directly the
percentage of HNO 3 in the original sample?
21. In the Dumas method for measuring the total nitrogen in an organic compound, the compound is mixed with CuO and heated in a stream of pure CO 2 .
All the gaseous products are passed through a heated tube of Cu turnings, to
reduce any oxides of nitrogen to N 2 , and then through a 50% solution of KOH
to remove the CO 2 and water. The N 2 is not absorbed, and its volume is
measured by weighing the mercury (density = 13.56 g/ml) that the N 2 displaces from the apparatus.
(a) A 20.1 mg sample of a mixture of glycine, CH 2 (NH 2 )COOH, and benzoic
acid, C 7 H 6 O 2 , yields N 2 at 730 torr and 21°C. This N 2 displaces 5.235 g of
mercury. Calculate the percentage of glycine in the original mixture.
(b) A 4.71 mg sample of a compound containing C, H, (), and N is subjected
to a Dumas nitrogen determination. The N 2 , at 735 torr and 27°C, displaces 10.5532 g of mercury. A carbon-hydrogen analysis shows that this
compound contains 3.90% H and 46.789r C. Determine the empirical
formula of this compound.
PROBLEMS B
22. Balance the following equations, which show the starting materials and the
reaction products. It is not necessary to supply any additional reactants or
products. A A sign indicates that heating is necessary.
(a) H 3 BO 3 -^ H 4 B 6 O U + H 2 O
(b) C 6 H 12 O 6 -> C 2 H 5 OH + C0 2
(c) CaC 2 + N 2 A. CaCN 2 + C
(d) CaCN 2 + H 2 O -> CaCO 3 + NH 3
(e) BaO + C + N 2 ± Ba(CN) 2 + CO
(f) C 6 H 6 + O 2 ± C0 2 + H 2 0
183
the reaction of concentrated H 2 SO 4 with nitrates in the presence of metallic
mercury, by the reaction
2KN0 3 + 4H 2 SO 4 + 3Hg -> K 2 SO 4 + 3HgSO 4 + 4H 2 O + 2NO
In a simple form of this apparatus, the NO is collected over water in a graduated tube and its volume, temperature, and pressure are measured. A 1.000 g
sample containing a mixture of KNO 3 and K 2 SO 4 is treated in this manner,
and 37.50 ml of NO is collected over water at a temperature of 23°C and a
pressure of 732.0 torr. Calculate the percentage of KNO 3 in the original sample.
20. A commercial laboratory wished to speed up its routine analysis for HNO 3 in
a mixture of acids, using the nitrometer mentioned in Problem 19. To do this, it
collects the NO over mercury, uses enough concentrated H 2 SO 4 to make
correction for water vapor unnecessary, thermostats its graduated tube at
25.0°C, and takes all pressure measurements at 730.0 torr. The tube is graduated to 100.0 ml. What weight of original acid sample should always be taken
so that the buret reading under these conditions also indicates directly the
percentage of HNO 3 in the original sample?
21. In the Dumas method for measuring the total nitrogen in an organic compound, the compound is mixed with CuO and heated in a stream of pure CO 2 .
All the gaseous products are passed through a heated tube of Cu turnings, to
reduce any oxides of nitrogen to N 2 , and then through a 50% solution of KOH
to remove the CO 2 and water. The N 2 is not absorbed, and its volume is
measured by weighing the mercury (density = 13.56 g/ml) that the N 2 displaces from the apparatus.
(a) A 20.1 mg sample of a mixture of glycine, CH 2 (NH 2 )COOH, and benzoic
acid, C 7 H 6 O 2 , yields N 2 at 730 torr and 21°C. This N 2 displaces 5.235 g of
mercury. Calculate the percentage of glycine in the original mixture.
(b) A 4.71 mg sample of a compound containing C, H, (), and N is subjected
to a Dumas nitrogen determination. The N 2 , at 735 torr and 27°C, displaces 10.5532 g of mercury. A carbon-hydrogen analysis shows that this
compound contains 3.90% H and 46.789r C. Determine the empirical
formula of this compound.
PROBLEMS B
22. Balance the following equations, which show the starting materials and the
reaction products. It is not necessary to supply any additional reactants or
products. A A sign indicates that heating is necessary.
(a) H 3 BO 3 -^ H 4 B 6 O U + H 2 O
(b) C 6 H 12 O 6 -> C 2 H 5 OH + C0 2
(c) CaC 2 + N 2 A. CaCN 2 + C
(d) CaCN 2 + H 2 O -> CaCO 3 + NH 3
(e) BaO + C + N 2 ± Ba(CN) 2 + CO
(f) C 6 H 6 + O 2 ± C0 2 + H 2 0