|
Past
paper questions 1
Francine
Taylor-Campbell, Contributor
In
this series of lessons we will examine
a few past-paper questions which should
help in your examination preparation.
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:
(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 oxidizing agent (ii) A reducing
agent
Explain
your answers.
(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 |
Decrease
in reactivity |
| H |
| 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.
2.
Chemical properties:
Metals
are reducing agents while non-metals
are oxidizing 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 oxidizing 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 oxidized).
(c)
2NaNO3 ====heat==== 2NaNO2
+ O2
2Cu(NO3)2
===heat===== 2CuO + 4NO2
+ O2
(d)
Based on figure 1 shown, magnesium
is the most reactive and copper is
the least reactive. 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.
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. A 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
Francine
Taylor-Campbell is an independent
contributor. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
|
