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Examining
past papers
Francine
Taylor-Campbell, Contributor
In
this series of lessons we will examine
a few past paper questions that will
help in your examination preparations.
Question
1
Metals
and non-metals exhibit different physical
and chemical properties. State TWO
differences between metals and non-metals
for EACH of the following properties:
(i)
Physical properties (ii) Chemical
properties
(b)
The electronic configuration of sodium
is 2,8,1, while that of chlorine is
2,8,7.
Which
ONE of these elements will act as:
(i)
An oxidising agent (ii) A reducing
agent.
Explain
your answer.
(c)
The way nitrates of metals decompose
depends on the position of the metal
in the reactivity series. With the
use of balanced equations, illustrate
this statement by the action of heat
on NaNO3 and Cu(NO3)2.
(d)
Figure 1 below shows the position
of three elements in the reactivity
series.
Mg
H
Decrease in reactivity
Cu
Fig.
1 Position of selected elements in
the reactivity series
Based
only on the position in the reactivity
series, which element would you select
for use in making containers to store
acidic fruit juices? Explain your
answer.
ANSWERS
1.
Physical properties
Metals
conduct electricity but non-metals
do not, (except for graphite).
Metals
generally have high melting and boiling
points while non-metals have low boiling
and melting points.
Chemical
properties
Metals
are reducing agents while non-metals
are oxidising agents.
Metals
react with oxygen to form basic oxides
while non-metals form acidic oxides.
(b)
Chlorine is a non-metal and will act
as an oxidising agent since it gains
electrons during chemical reactions
(becomes reduced).
Sodium
is a metal and will act as a reducing
agent, losing electrons during reactions
(becomes oxidised).
(c)
2NaNO3 ====heat==== 2NaNO2 + O2
2Cu(NO3)2
===heat===== 2CuO + 4NO2 + O2
(d)
Based on figure 1, magnesium is the
most reactive and copper is the leas.
A reactive metal would be expected
to react with acids, hence the container
must be made of a material that is
not reactive towards acids. Copper
would be the best element to be used
in the container since it is the least
reactive.
Now
attempt this question as part of your
preparation.
2.
EDTA, a complexing agent, can be used
in volumetric analysis for the determination
of Zn2+ ions. One mole of EDTA reacts
completely with one mole of Zn2+.
In the hydrolysis of hydrated zinc
crystals for its zinc content, 0.86
g of the zinc salt completely dissolved
in 100 cm3 of distilled water. 25
cm3 sample of this solution was then
titrated against a 0.05 mol dm-3 solution
of EDTA. 10.00 cm3 of EDTA were used.
Calculate
(a) the number of moles of EDTA in
10.00 cm3 of this solution
(b)
the number of moles of Zn2+ in 25
cm3 of this solution
(c)
the mass of Zn2+ in 100 cm3
of this solution
(d)
the percentage zinc in the hydrated
zinc sulphate crystals.
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Students
listen attentively during the
CXC symposium on information
technology at Bridgeport High
School on April 12.
- Anthony Minott/Freelance
Photographer
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Francine
Taylor-Campbell is an independent
contributor.
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