Page 122 - Theory and Problems of BEGINNING CHEMISTRY

CHAP. 7] FORMULA CALCULATIONS 111

7.16. (a) How many socks are there in 10 dozen pairs of socks? (b) How many hydrogen atoms are there in
10.0 mol of hydrogen molecules?
12 pairs socks 2 socks

Ans. (a) 10 dozen pairs socks = 240 socks
1 dozen pairs socks 1 pair socks
23

6.02 × 10 H 2 2H 25
(b) 10.0 mol H 2 = 1.20 × 10 H atoms
1 mol H 2 1H 2
7.17. What is the difference between 1 mol of nitrogen atoms and 1 mol of nitrogen molecules?
Ans. The nitrogen molecules contain two nitrogen atoms each; hence 1 mol of nitrogen molecules contains
twice as many atoms as 1 mol of nitrogen atoms. A mole of nitrogen molecules contains 2 mol of bonded
N atoms.

7.18. Show that the ratio of the number of moles of two elements in a compound is equal to the ratio of the
number of atoms of the two elements.
6.02 × 10 atoms A
23
x mol A
Ans. x mol A = 1 mol A = x atoms A
23
1 mol B 6.02 × 10 atoms B 1 atom B
1 mol B
1 mol B
7.19. How many moles of each substance are there in each of the following masses of substances? (a) 111 g
F 2 ,(b) 6.50 g Na, (c) 44.1 g NaOH, (d) 0.0330 g NaCl, (e) 1.96 g (NH 4 ) 2 SO 3 ,( f ) 7.22 g NaH 2 PO 4

1 mol F 2
Ans. (a) 111gF 2 = 2.92 mol F 2
38.0gF 2

1 mol Na
(b)6.50gNa = 0.283 mol Na
23.0gNa

1 mol NaOH
(c)44.1 g NaOH = 1.10 mol NaOH
40.0 g NaOH

1 mol NaCl
(d)0.0330 g NaCl = 5.64 × 10 −4 mol NaCl
58.5 g NaCl

1 mol (NH 4 ) 2 SO 3
(e)1.96 g (NH ) 2 SO 3 = 0.0169 mol (NH 4 ) 2 SO 3
4
116 g (NH ) 2 SO 3
4

1 mol NaH 2 PO 4
( f )7.22 g NaH PO 4 = 0.0602 mol NaH 2 PO 4
2
120 g NaH PO 4
2
7.20. In 2.50 mol Ba(NO 3 ) 2 ,(a) how many moles of barium ions are present? (b) How many moles of nitrate
ions are present? (c) How many moles of oxygen atoms are present?
Ans. (a) 2.50 mol Ba 2+ ions
(b) 5.00 mol NO 3 ions
−
(c) 15.0 mol O atoms
7.21. Without doing actual calculations, determine which of the following have masses greater than 1 mg: (a)
23
23
1CO 2 molecule, (b) 1 amu, (c)6.02 × 10 H atoms, (d) 1 mol CO 2 ,(e)6.02 × 10 amu, ( f ) 1
6.02×10 23
mol H atoms
Ans. (c), (d), and (e) have masses greater than 1 mg.
7.22. What is the mass of each of the following? (a) 6.78 mol NaI, (b) 0.447 mol NaNO 3 ,(c) 0.500 mol BaO 2 ,
(d) 5.44 mol C 8 H 18