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More
on metals and non-metals
Francine
Taylor-Campbell, Contributor
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| Ardenne
High's 2005 Schools' Challenge
Quiz team: (From left) Theodore
Henry, Duane Brissett, Dwayne
Dixon and Dane Clarke (captain).
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PLEASE
ATTEMPT the following questions on the
topic:
1.
When manganese (II) nitrate Mn(NO3)2
is heated the only products are manganese
(IV) oxide and a brown gas Q. When
manganese (IV) oxide is added to hydrogen
peroxide, a colourless gas R is given
off. R relights a glowing splint.
When manganese (IV) oxide is added
to hot concentrated hydrochloric acid
a yellow-green gas is given off. S
bleaches damp litmus paper.
(a)
Identify the gases represented by
the letters Q, R and S.
(b)
State the formula of manganese (IV)
oxide
(c)
Write equations for the action of
heat on (i) sodium nitrate (ii) lead
(II) nitrate
(d)
Oxygen can react with metals and non-metals
to form oxides. Write a balanced equation
to show how oxygen reacts with (i)
sodium (ii) sulphur
(e)
What would you observe if water is
added to the product formed in each
of the reactions and the solution
tested with a few drops of litmus
solution?
2.
A student conducted a number of tests
on an aqueous solution of compound
X. The observations made are recorded
on the table below. You are required
to fill in the inferences that could
be made based on the observations
recorded. (See table)
| TEST |
OBSERVATIONS |
INFERENCES |
| (i)
To a sample of Solution X, dilute
nitric acid was added, followed
by a few drops of silver nitrate
solution. |
No
precipitated formed |
|
| (ii)
To a sample of Solution X, a few
copper turnings were added, followed
by concentrated sulphuric acid. |
Brown
fumes evolved, turned moist blue
litmus red |
|
| (iii)
To a sample of Solution X, aqueous
sodium hydroxide was added, until
in excess. |
White
precipitate soluble in excess |
|
| (iv)
To a sample of Solution X, aqueous
ammonia was added, until in excess |
White
precipitate soluble in excess |
|
| (v)
To a sample of Solution X a few
drops of acidified potassium manganate
(VII) solution were added and
the solution heated. |
The
potassium manganate (VII) solution
was not decolourized. |
|
| (vi)
To a sample of Solution X, dilute
hydrochloric acid was added, followed
by a few drops of barium chloride
solution. |
White
precipitate formed. |
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ANSWERS
2.
INFERENCES
(i)
No halide ion is present i.e. Cl-,
Br- and I-
(ii)
Brown fumes indicate that the gas
is nitrogen dioxide (NO2). It turns
moist blue litmus red because it is
an acidic gas. NO3- ion present.
(iii)
White ppt soluble in xs aqueous NaOH
suggests that either Zn2+, Al3+, and
Pb2+ may be present.
(iv)
White precipitate soluble in excess
aqueous ammonia confirms that of the
3 cations in (iii) the one present
is Zn2+
(v)
Potassium manganate (VII) was not
reduced by Solution X. The possible
ions that could do this are SO32-
and S2- (remember the halide ions
are already ruled out). This means
that SO32- is not present.
(vi)
The ion present is SO42- as it is
the only ppt formed with barium ions
that does not dissolve in acid.
1.
(a) The gases Q, R, S are nitrogen
dioxide (NO2), oxygen (O2), and chlorine
(Cl2) respectively.
(b)
Formula of manganese (IV) oxide -
MnO2
(c)
2NaNO3(s) ===== 2NaNO2(s) + O2(g);
2Pb(NO3)2 ==== 2PbO(s) + 4NO2(g) +
O2 (g)
(d)
Na (s) + O2(g) === 2Na2O(s); S (s)
+ O2(g) ==== SO2 (g)
(e)
A very vigorous reaction would take
place when water is added to sodium
oxide, which would also dissolve.
This solution would cause no change
to the blue litmus solution. The sulphur
dioxide produced would dissolve in
the water forming a solution which
would change the blue litmus solution
to red.
*
Francine Taylor-Campbell is
an independent contributor.
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