How does the law of conservation of matter apply to chemical and physical
changes? Provide a reaction in each case to support your answer. (4
marks)
SOLUTION
Yes, the law of conservation of mass applies to physical changes. The law of
conservation of mass states that in a chemical reaction mass is neither created nor
destroyed.
Example
The carbon atom in coal becomes carbon dioxide when it is burned. The carbon atom
changes from a solid structure to a gas but its mass does not change.
C(s) + O2(g) -> CO2(g)
QUESTION 2
(a) Design an experiment to separate a given heterogeneous mixture into its
individual components. (You do not need to use chemistry equipment, what
everyday items could you use?)
SOLUTION
(a) Magnetic separation
The following diagram shows how magnetic separation can be used to separate a
mixture of components. In the example, mineral ore that contains two compounds (one
magnetic, and the other non-magnetic) is being separated. The ore grains are fed onto a
revolving belt. The roller on the end of the belt is magnetic. This means that all the
magnetic grains in the ore will stick to the belt when it goes around the roller, while the
non-magnetic grains will fall off the end. As soon as the magnetic grains move past the
magnetic roller, they will also fall down.
Page 2 of 17
, b.) Would you be able to separate a homogenous mixtures ? Explain why you would
say yes or no. (3 marks)
SOLUTION
Evaporation
Evaporation is a technique used to separate out homogeneous mixtures that contain
one or more dissolved salts. The method drives off the liquid components from the solid
components. The process typically involves heating the mixture until no more liquid
remains. Prior to using this method, the mixture should only contain one liquid
component, unless it is not important to isolate the liquid components. This is because
all liquid components will evaporate over time. The evaporation method is suitable to
separate a soluble solid from a liquid.
In many parts of the world, table salt is obtained from the evaporation of sea water. The
heat for the process comes from the sun.
Page 3 of 17
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