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Revision
lessons
Francine
Taylor-Campbell, Contributor
We
will continue to examine a few past
paper questions that will help in
your examination preparations.
Question
one
A
group of students added an excess
of finely divided zinc metal to aqueous
sulphuric acid. When no more gas was
evolved they filtered the mixture
and used the filtrate to obtain dry
crystals of hydrated zinc sulphate.
One mole of these crystals contained
seven moles of water of crystallisation.
a)
Write a balanced chemical equation
for the reaction between zinc and
aqueous sulphuric acid.
b)
Write the chemical formula for hydrated
zinc sulphate crystals.
c)
Describe three important steps the
students should follow to obtain dry,
hydrated zinc sulphate crystals from
the filtrate.
Answer
a)
Zn (s) + H2SO4
(aq) ==== ZnSO4 (aq) +
H2 (g)
b)
ZnSO4.7H2O -
hydrated zinc sulphate
c)
The steps to be taken to obtain dry,
hydrated zinc sulphate crystals are
as follows:
i)
Boil the filtrate in an evaporating
dish
ii)
Do not evaporate to dryness instead
boil to a small volume
iii)
Allow the solution to cool then collect
the crystals formed.
Continue
to prepare for your exams by practising
the questions below and remember to
read the questions carefully!
Question
two
2.
When lead nitrate is strongly heated,
it decomposes to give lead (II) oxide,
nitrogen dioxide and oxygen.
a)
Write a balanced equation for the
action of heat on lead nitrate.
b)
How would you know that nitrogen dioxide
is given off in the reaction?
c)
Determine the change in the oxidation
number of nitrogen during the reaction.
Show how you arrived at your answer.
d)
Calculate the volume of nitrogen dioxide
that would be given off at room temperature
and pressure when 3.31g of lead nitrate
were strongly heated until no more
reaction took place.
e)
How do the products obtained upon
heating lead nitrate differ from those
obtained upon heating sodium nitrate?
f)
Explain why metal alloys are often
used in place of pure metals.
g)
Name a metal alloy and state its use.
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Jamaica's
future scientists test their
skills during a chemistry lab
at the Winston Jones High School
recently.
Photo by Michael Lee
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Francine
Taylor-Campbell is an independent
contributor.
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