Page 123 - Theory and Problems of BEGINNING CHEMISTRY

112 FORMULA CALCULATIONS [CHAP. 7

150 g NaI
Ans. (a)6.78 mol NaI = 1020 g NaI
1 mol NaI
85.0 g NaNO 3

(b)0.447 mol NaNO 3 = 38.0 g NaNO 3
1 mol NaNO 3

169 g BaO 2
(c)0.500 mol BaO 2 = 84.5 g BaO 2
1 mol BaO 2

114gC H 18
8
(d)5.44 mol C 8 H 18 = 620gC 8 H 18
1 mol C 8 H 18
7.23. In 0.125 mol NaClO 4 ,(a) how many moles of sodium ions are present? (b) how many moles of
perchlorate ions are present?
+
Ans. (a) 0.125 mol Na ions (b) 0.125 mol ClO 4 ions. The subscript 4 refers to the number of O atoms per
−
anion, not to the number of anions.
7.24. (a) Calculate the formula mass of H 3 PO 4 .(b) Calculate the number of grams in 1.00 mol of H 3 PO 4 .
(c) Calculate the number of grams in 2.00 mol of H 3 PO 4 .(d) Calculate the number of grams in 0.222
mol of H 3 PO 4 .
Ans. (a) 3 H 3.02 amu (b) 97.99 g
P 30.97 amu 97.99 g
(c) 2.00 mol = 196 g
4 O 64.00 amu 1 mol
total 97.99 amu 97.99 g
(d) 0.222 mol = 21.8g
1 mol
7.25. (a) Determine the number of moles of ammonia in 27.5 g of ammonia, NH 3 .(b) Determine the number
of moles of nitrogen atoms in 27.5 g of ammonia. (c) Determine the number of moles of hydrogen atoms
in 27.5 g of ammonia.

1 mol NH 3
Ans. (a) 27.5 g NH 3 = 1.62 mol NH 3
17.0gNH 3
1 mol N

(b) 1.62 mol NH 3 = 1.62 mol N
1 mol NH 3
3 mol H

(c) 1.62 mol NH 3 = 4.86 mol H
1 mol NH 3
7.26. How many hydrogen atoms are there in 1.00 mol of methane, CH 4 ?
6.02 × 10 CH 4 molecules 4 H atoms
23
24
Ans. 1 mol CH 4 = 2.41 × 10 H atoms
1 mol CH 4 1CH 4 molecule
7.27. Determine the number of mercury atoms in 7.11 g of Hg 2 Cl 2 .
23
1 mol Hg Cl 2 2 mol Hg 6.02 × 10 Hg atoms 22
2
Ans. 7.11gHg Cl 2 = 1.81 × 10 atoms
2
472gHg Cl 2 1 mol Hg Cl 2 1 mol Hg
2
2
7.28. (a) If 1 dozen pairs of socks weighs 11 oz, how much would the same socks weigh if they were unpaired?
(b) What is the mass of 1 mol O 2 ? What is the mass of the same number of oxygen atoms unbonded to
one another?
Ans. (a) The socks would still weigh 11 oz; unpairing them makes no difference in their mass.
(b) The mass of 1 mol O 2 is 32 g; the mass of 2 mol O is also 32 g. The mass does not depend on whether
they are bonded.
7.29. How many molecules are there in 1.00 mol F 2 ? How many atoms are there? What is the mass of 1.00
mol F 2 ?