Ap Chemistry Worksheet - Dr. Kathleen Gorski, Wilbraham And Monson Acaddemy Page 6
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243.24 Calculate the percentage by mass of the indicated element in the following compounds: (a)
carbon in acetylene, C
H
, a gas used in welding; (b) hydrogen in ascorbic acid, HC
H
O
, also
2
2
6
7
6
known as vitamin C; (c) hydrogen in ammonium sulfate, (NH
)
SO
, a substance used as a
4
2
4
nitrogen fertilizer; (d) platinum in PtCl
(NH
)
, a chemotherapy agent called cisplatin; (e)
2
3
2
oxygen in the female sex hormone estradiol, C
H
O
; (f) carbon in capsaicin, C
H
NO
, the
18
24
2
18
27
3
compound that gives the hot taste to chili peppers.
3.27 (a) What is Avogadro’s number, and how is it related to the mole? (b) What is the
relationship between the formula weight of a substance and its molar mass?
3.34 Calculate the following quantities:
-2
(a) mass, in grams, of 1.50 x 10
mol of CdS
(b) number of moles of NH
Cl in 86.6 g of this substance
4
-2
(c) number of molecules in 8.447 x 10
mol C
H
6
6
-3
(d) number of O atoms in 6.25 x 10
mol Al(NO
)
3
3
3.53 (a) Combustion analysis of toluene, a common organic solvent, gives 5.86 mg of CO
and
2
1.37 mg of H
O. If the compound contains only carbon and hydrogen, what is its empirical
2
formula? (b) Menthol, the substance we can smell in mentholated cough drops, is composed of
C, H, and O. A 0.1005-g sample of menthol is combusted, producing 0.2829 g of CO
and
2
0.1159 g of H
O. What is the empirical formula for menthol? If menthol has a molar mass of
2
156 g/mol, what is its molecular formula?
3.68 The complete combustion of octane, C
H
, the main component of gasoline, proceeds as
8
18
follows:
2 C
H
(l) + 25 O
(g) ! 16 CO
(g) + 18 H
O (g)
8
18
2
2
2
(a) How many moles of O
are needed to burn 1.50 mol of C
H
?
2
8
18
(b) How many grams of O
are needed to burn 10.0 g of C
H
?
2
8
18
(c) Octane has a density of 0.692 g/mL at 20 °C. How many grams of O2 are required to burn
15.0 gal of C
H
(the capacity of an average fuel tank)?
8
18
(d) How many grams of CO
are produced when 15.0 gal of C
H
are combusted?
2
8
18
3.78 One of the steps in the commercial process for converting ammonia to nitric acid is the
(g) ! 4 NO (g) _ 6 H
conversion of NH
to NO:
4 NH
(g) + 5 O
O (g)
In a
3
3
2
2
certain experiment, 2.00 g of NH
reacts with 2.50 g of O
(a) Which is the limiting reactant?
3
2
(b) How many grams of NO and of H
O form? (c) How many grams of the excess reactant
2
remain after the limiting reactant is completely consumed? (d) Show that your calculations in
parts (b) and (c) are consistent with the law of conservation of mass.
3.86 If 1.5 mol of C
H
OH, and 1.5 mol C
H
, and 1.5 mol of CH
CH
COCH
are completely
2
5
3
8
3
2
3
combusted in oxygen, which produces the largest number of moles of H
O? Which produces
2
the least? Explain.
[3.94] An organic compound was found to contain only C, H, and Cl. When a 1.50-g sample of
the compound was completely combusted in air, 3.52 g of CO
was formed. In a separate
2
experiment the chlorine in a 1.00-g sample of the compound was converted to 1.27 g of AgCl.
Determine the empirical formula of the compound.
6
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