HOMEWORK: WEEK 1 FOR WEEK 2.
CHAPTER 1.
1.10
A glass of bubbling carbonated beverage with ice cubes contains three phases, gas,
liquid, and solid.
A moredetailed approach: “I see lumps of ice: these are solid
water. These are floating in the
liquid
beverage (liquids flow, unlike solids). The bubbles contain gas
(probably carbon dioxide).
Gases are less dense than liquids, so I see the bubbles rising through the liquid.”
1.13
Multiplication and division rule: the precision is determined by the number with the
smallest number of sig. figs. In performing the calculation 100.0 x 0.0634 ÷ 25.31, the
calculator display shows 0.2504398. We would report the answer as 0.250 because the
factor 0.0634 has the least number of significant figures (three).
Addition and subtraction rule: the precision is determined by the number with the smallest
number of digits after the decimal point. In performing the calculation 184.2 + 2.324, the
calculator display shows 186.524. Because the quantity 184.2 has the least number of
decimal places (one), the answer is reported as 186.5. Similarly for the sum:
5.2 x 10
3
+ 1.48 x 10
3
, the answer would be written as 6.7 x 10
3
or 6700
1.18
Units should be carried along because first, the units for the answers will come out in the
calculations, and second, if you make an error in arranging factors in the calculation, this
will become apparent because the final units will be nonsense.
In addition: The numbers in a calculation usually represent physical quantities. Without its units,
the value is not properly defined. For instance, an air temperature of 30
o
is meaningless unless
we have units: 30
o
C is quite warm; 30
o
F is below freezing and 30K is indescribably cold. Thus to
express the value of a quantity fully, we must write units as well as a number.
010
The answer is c, three significant figures. For addition, it is best to write the numbers in
decimal format, thus: 12.9 + 0.02. Only the first digit after the decimal point is significant,
so the answer is 12.9, which has a total of 3 sig figs.
020
The answer is c, 0.23 mg. I recommend converting each number to the same base unit. The
simplest is the gram, because we can just use the definitions of the metric prefixes. Thus:
a) 23cg = 23 x 10
2
g = 0.23g = 2.3 x 10
1
g
b) 2.3 x 10
3
μ
g = 2.3 x 10
3
x 10
6
g = 2.3 x 10
3
g
c) 0.23 mg = 0.23 x 10
3
g = 2.3 x 10
4
g: the smallest!!
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 Spring '06
 Dr.Huston
 Chemistry, Decimal, Sig Figs, Arithmetic precision, sig. figs

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