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Oxygen can be prepared from
a colourless liquid called hydrogen peroxide (H 2 O 2 ) - which
can be purchased from Guardian Pharmacy. It is usually kept in a
dark bottle to prevent its decomposition to water and gaseous oxygen
as light can catalyse the decomposition.
Because of its ability to yield oxygen - it is
marketed for its antiseptic properties, such as for the cleaning
of wounds and for mouthwash. However it must be used in diluted
form. A bottle of hydrogen peroxide costs about S$2.
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The decomposition of hydrogen
peroxide into water and oxygen - if it is to be done at room temperature
- has to be catalysed by a black powder called manganese dioxide
(MnO 2 ) also known as manganese (IV) oxide.
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H2O2(l)→
H2O(l) + O2(g)
or 2H2O2(l) →
2H2O(l) + O2(g)
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Adele has to test for herself that the
presence of oxygen, this can be detected by a glowing splint
being relighted (rekindled) into a flame. We have ascertained
that sometimes the sudden bursting of the glowing splint into
a flame could be accompanied by a 'pop' sound - but this, by
no means, implies that the gas produced is hydrogen. To test
for hydrogen you need a lighted (burning) splint. Kindly refer
to Mr Peter Lim's coloured Qualitative Analysis book for more
details and other ways of preparing oxygen.
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Thermal Decomposition of Lead
(IV) Oxide
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Now, another way of producing oxygen is by the
decomposition of a black oxide of
lead called lead (IV) oxide, PbO2. It can decompose
to an orange and yellow
oxides of lead as the test tube below shows.
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Let's get down
to theory:
4PbO2 →
Pb3O4 + PbO
+ ½ O2
or 8PbO2 →
2Pb3O4 +
2PbO + O2
However, red
oxide of lead can be heated to produce
oxygen and yellow lead oxide
as the close up of the picture shows.
Question: Which one of the oxides of
lead contains the highest % of oxygen and which one contains the
lowest?
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