Page 45 - Theory and Problems of BEGINNING CHEMISTRY

34 MATHEMATICAL METHODS IN CHEMISTRY [CHAP. 2

TEMPERATURE SCALES
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2.70. Convert −40 F to degrees Celsius.
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◦ C = ( F − 32 ) = (−40 − 32 ) =−40 C
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Ans. 9 9
2.71. Change the following temperatures in degrees Celsius to kelvins: (a)15 C, (b) −15 C, and (c) −265 C.
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Ans. (a) 15 C + 273 = 288 K
(b) −15 C + 273 = 258 K
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(c) −265 C + 273 = 8K
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2.72. Change the following temperatures in kelvins to degrees Celsius: (a) 330 K, (b) 282 K, and (c) 302 K.
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Ans. (a)57 C(b)9 C(c)29 C
Supplementary Problems
2.73. Change 42.30 km/h to meters per second.
42.30 km 1000 m 1h 1 min

Ans. = 11.75 m/s
h 1km 60 min 60 s
2.74. Match the value on the first line below with each corresponding value on the second line. (More than one value might
correspond for each.)
1 µL 1kL 1L 1mL
0
3
1dm 3 1cm 3 1mm 3 1m 3 10 L10 −3 L10 L10 −6 L
3
0
3
Ans. 1 µL = 1mm = 10 −6 L 1 L = 1dm = 10 L
3
3
3
1kL = 1m = 10 L 1 mL = 1cm = 10 −3 L
2.75. What exponential number best represents each of the following metric prefixes? (a) deci, (b) nano, (c) centi,
(d ) micro, (e) milli, and (f ) kilo
Ans. (a)10 −1 (b)10 −9 (c)10 −2 (d)10 −6 (e)10 −3 (f)10 3
2.76. A certain beaker has a mass of 141.2 g. When 13.0 mL of an organic liquid is placed in the beaker, the total mass is
150.5 g. Calculate the density of the liquid to the proper number of significant digits.
Ans. The mass of the liquid is 150.5g − 141.2g = 9.3g.
Its density is (9.3 g)/(13.0 mL) = 0.72 g/mL.

2.77. A beaker plus contents has a combined mass of 130.3 g. The beaker has a mass of 129.1 g. If the density of the
contents is 2.04 g/mL, what is the volume of the contents to the correct number of significant digits?
1mL

Ans. (130.3g − 129.1g) = 0.59 mL
2.04 g
There are only two significant digits since the subtraction yields an answer with two significant digits. That
answer limits the final volume to two significant digits.
2.78. Make the following English-metric conversions:

(a) Change 4.22 in. to cm (d) Change 21.7 lb to grams
(b) Change 2.35 kg to pounds (e) Change 60.0 mi/h to meters per second
2
(c) Change 6.13 L to fluid ounces (f) Change 3.50 in. to cm 2