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Metals
and non-metals (cont'd)
Francine
Taylor-Campbell, Contributor
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
is tested with a few drops of litmus
solution?
ANSWERS
1.
(a) The gases Q, R, S are nitrogen
dioxide (NO2), oxygen (O2), and chlorine
(Cl2), respectively.
(a)
Formula of manganese (IV) oxide -
MnO2
(b)
2NaNO3(s) ===== 2NaNO2(s) + O2(g);
2Pb(NO3)2 ==== 2PbO(s) + 4NO2(g) +
O2 (g)
(c)
Na (s) + O2(g) === 2Na2O(s); S (s)
+ O2(g) ==== SO2 (g)
(d)
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.
See
table below.
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Test
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Observations
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Inferences
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| (i)
To a sample of Solution X, dilute
nitris acid was added, followed
by a few drops of silver nitrate
solution. |
No
precipitate formed
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| (ii)
To a sample of Solution X, a few
copper turnings were added, folowed
by concentrated sulphuric acid. |
Brown
fumes evolved, turned moist
blue litmus red
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| (iii)
To a sample of Solution X, aqueous
sodium hydroxide was added, until
in excess. |
White
precipitate soluble in excess
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(iv)
To a sample of Solution X, aqueous
ammonia was added, until in excess
(v) To a sample of Solution X
a few drops of acidified potassium
manganate (VII) solution were
added, and the solution heated.
(vi) To a sample of Solution X,
dilute hydrochloric acid was added,
followed by a few drops of barium
chloride solution. |
White
precipitate soluble in excess
The Potassium manganate (VII)
solution was not decolourized.
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
three 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 the
only ppt formed with barium ions that
does not dissolve in acid.
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Matthew
Coley discusses his masterpiece,
'Destruction - Smoking Kills',
with his art and craft teacher,
Lurlene Bryan-Davis, during
an exhibition at Bridgeport
High School, recently.
-Anthony Minott/Freelance Photographer
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Francine
Taylor-Campbell is an independent
contributor.
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