8.1 Consider the diagram below that shows liquid water evaporating to form water
vapour.
Use chemical formulae to represent the process in the diagram above and
indicate the phases of the substance undergoing this process. (2)
8.2 Give THREE separation methods that can be used to reverse a physical
change. (3)
8.3 Two Grade 10 learners investigate whether mass is conserved during a
reaction. They burn 5 g of magnesium in oxygen to form a white powder,
magnesium oxide.
The following balanced chemical equation represents the chemical reaction
that took place in the investigation above.
8.3.1 Write down:
(a) An investigative question for this investigation (2)
(b) An independent variable of this investigation (1)
(c) The dependent variable of this investigation (1)
(d) The variable that was kept constant in this investigation (1)
8.3.2 Is this reaction a SYNTHESIS or DECOMPOSITION? Give a reason for
your answer. (2)
8.3.3 When a white powder of magnesium oxide was formed in the above
investigation, heat was given off. Give the term that best describes the
underlined phrase. (1)
8.3.4 Write down the law of conservation of mass in words. (2)
8.3.5 Show by means of a calculation that mass is conserved during the
reaction represented by the balanced equation in QUESTION 8.3. (4)
8.3.6 MgO is the chemical formula of the chemical substance formed during
the chemical reaction represented by the balanced chemical equation
above.
Study the chemical formula of this substance and answer the
following questions.
(a) Give the term used to describe the substance formed in the
chemical reaction. (1)
(b) Calculate the percentage of oxygen in a 20 g sample of
magnesium oxide produced. (4)
[24]