b
a
gas to liquid.
liquid to gas at a precise temperature
liquid to solid
.
ethanol
-182
-117
-164
b
a
What effect does the presence of an impurity have on t_he freezing point of a liquid?
Which two substances are liquids at room temperature? Explain your answer.~)
All three substances have negative values for their melting point. Which of them has the lowest melting point?
357
c
What do you understand by the word volatile when used in chemistry?
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a
Put these three liquids in order of volatility, with the most volatile first: water (b.p. 10~ °C), ethanoic acid (b.p. 128 °C) and
ethanol (b.p. 78 °C).
mercury
-30
I
Table 1.3: Melting and boiling points of ethanol, methane and mercury.
methane
iSubstancc;
The melting and boiling points of three pure substances are given In Table 1.3.
c
State the names for the following physical changes:
Questions
1
2
3
b
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5
5
10
5
15
7
20
25
13
28
30
45
35
40
62
76
45
79
so
55
82
60
82
1 A sample of a solid substance, which had been cooled to -5 °c, was put Into a test-tube.
The test-tube was then heated In a water bath. The temperature of the substance was taken every
-5
5 minutes for an hour. The results obtained are shown below.
Time/min
Temperature/°C
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a Plot the results on the graph paper below, putting time on the horizontal axis and temperature
on the vertical axis.
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60
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b What Is the melting point of the substance? ......
c What Is the boiling point of the substance? .....:!:.S'.~.....
d Describe what Is happening to the particles of ~he substance after SO minutes.~
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