Homework 1 Answer Key
Chapter 3
30. a) Element b) Compound
c) Element
d) Element
32. a) homogeneous (as long as there are no air bubbles in it.)
b) heterogeneous
c) heterogeneous
d) homogeneous (as long as there is no sediment/solids)
34. a) Mixture; homogeneous (unless it is cloudy, with bacteria or white blood cells, for example)
b) Pure substance; compound
c) Mixture; heterogeneous
d) Mixture; heterogeneous
36. All are physical, except c. Notice that in part b, better wording would have been “temperature at which dry ice
sublimates.”
38. Chemical props of ozone include “very reactive” and “decomposes upon exposure to UV light.” The others are physical.
40. A and c are physical changes; the others are chemical.
42. A is physical; B is chemical.
Chapter 2
30. 6.661x109
1.321 x109
1.147 x107
4.235 x106
-9
-1
-12
32. 1x10
1.43 x10
1x10
1 x10-6
34. 0.0000000000000000450
13700000000 5000000000
44
38. 0.0042
3.15171x108
0.000000000018
1.232x106
39. Notice that for each of these measurements, the estimated digit may vary, and this is okay!
a) 54.9 mL
b) 48.7°C
c) 46.83°C
d) 64 mL
40. Again, the last digit will vary between students, because it is estimated.
b) 55.38 mL
c) 7.19 mL
44. a) 5
b) 5
c) 3
d) 2
46. B is incorrect; should be 2 s.f. D is also wrong; should be 3 s.f.
48. a) 9.85x103
b) 1.55x1012
c) 2.35
d) 0.0000454
50. a) 65.7
b) 65.7
c) 65.8
d) 65.8
54.
56. a) 6x102 (only 1 s.f.) b) 6.4x102
c) 2
d) 223
58. a and b are correct. c should be 0.055098 and d should be 54.61
60. a) 1473.4
b) 0.103
c) 411
d) 4.2
2. This is important because the number of significant figures is a reflection of the degree of precision (or, the amount of
uncertainty) in a measurement. If you write a number with the incorrect number of significant figures, you will be
misrepresenting the amount of precision in the measurement.
A. 1, 3, 4 and 5 describe physical properties; 2 and 6 are chemical.
B. 1) Chemical; in combining with air, a new substance (silver sulfide) is produced.
2) This is a physical change, because as oil separates and floats no reactions are occurring.
3) Physical; the texture and cutting of an object do not involve reactions.
4) Physical; the separation of a mixture is a physical process.
5) Chemical; new substances (a mixture of gases) are produced, and “decomposition” is always a chemical change.
C. 1. Mixture, heterogeneous (if you consider the fact that there are solid particles of soot.)
2. Mixture, heterogeneous.
3. Pure substance; compound.
4. Pure substance; element.
5. Mixture; heterogeneous (unless it were completely free of pulp.)
6. Pure substance; compound.
D. 1, 2 and 3 are exact; the others are not.
E. (not required for the night section)
a.
_0.01_ L ≡ _1_ cL
b.
_1000_ g ≡ _1_ kg
c.
_1_ µm ≡ _0.000001_ m
d.
__1__ mg ≡ _0.001_ g
e.
_1000_ m ≡ _1_ km
f.
_0.01_ L ≡ _1_ cL
g.
_0.000001_ g ≡ 1_ µg
h.
_0.001_ L ≡ _1_ mL
i.
_0.01_ g ≡ _1_ cg