CH107 SPECIMEN EXAM-TYPE QUESTIONS (2)
Chapter 3
The questions are worth equal points
1. Uranium is a silver-white, lustrous, radioactive metal that is primarily found in
pitchblende, U3O8. The pure uranium is extracted from the pitchblende through a
series of chemical processes. The three allotropes of uranium, the α-, β-, and γforms, possess melting points between 667.7oC - 1132.3oC. Uranium forms
tetrahalide compounds (e.g. UF4) when heated in the presence of a halogen.
Uranium also produces hydrogen gas and uranium salts when mixed with an
acid. The half-life (t1/2) of uranium is approximately 4.51 x 109 years, and the
metal possesses a density of 19.05 g/mL.
Make a list of the terms in italics and classify them as physical or chemical
properties.
2. Pumice is a volcanic rock that contains a large number of trapped air bubbles.
A 155 g sample is found to have a volume of 163 mL.
(a) What is the mass of a 5.15 L sample?
(b) Will pumice float or sink in water?
(c) Will pumice float or sink in ethanol?
3. Classify the following materials as pure substances or mixtures. For mixtures,
classify them as homogeneous or heterogeneous. For pure substances, classify
them as elements or compounds.
(a) laughing gas (b) table salt (as bought in a store) (c) deionized and distilled
water (d) pewter (e) petroleum oil (f) well water (g) air (h) sodium chloride (i)
spectroscopic quality hexane (j) makkoli.
4. While studying an unknown, solid substance, you make the following
observations: (1) It has a uniform appearance. (2) It melts sharply upon heating
to a particular temperature. (3) After further vigorous heating it merely vaporizes.
How would you classify this substance?
5. A piece of unknown metal, thought to be lead (Pb) weighs 370 g. If it is heated
to 42.8 oC and then plunged carefully into 100.0 mL of water originally at 25.0 oC,
the final steady temperature of the water and lead is 26.8 oC. Is the metal lead?
Show working.
Solutions
1.
lustrous (physical property)
melting points (physical properties)
forms tetrahalide compounds (chemical property)
produces hydrogen gas and uranium salts (chemical property)
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density (physical property)
2.
(a) Density of pumice = 155 g/163 mL = 0.951 g/mL; a 5.15 L sample will weigh
0.951 g/mL x 5.15 x 103 mL = 4898 g or 4.90 kg
(b) It will float in water (density = 1.00 g/mL)
(c) It will sink in ethanol (density = 0.790 g/mL)
3.
(a) pure substance, compound (b) mixture (c) pure substance, compound (d)
mixture (e) mixture (f) mixture (g) mixture (h) pure substance, compound (i) pure
substance, compound (j) mixture
4.
Its uniform appearance suggests that it is not a heterogeneous mixture. The fact
that it melts sharply indicates that it is a pure substance (not a homogeneous
mixture), which is supported by the observation that it merely vaporizes on
further heating (with no separation or decomposition). It is either a pure element
or a heat-stable pure compound.
5.
Heat lost by metal = heat gained by water
-370 (g) x sp. ht. (J/g/oC) x (26.8 – 42.8) (oC) = 100.0 (g) x 4.18 (J/g/oC) x (26.8 –
25.0) (oC).
From which, Specific heat of metal = 0.127 J/g/oC. It is lead (sp. ht. = 0.128
J/g/oC)
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