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Chemistry igcse 0620/33 may/june 2011

Hey guys anyone know how to solve question (IV)

Hydrocarbons are compounds which contain only carbon and hydrogen.
(a) 20 cm3
of a gaseous hydrocarbon was burned in 120 cm3
of oxygen, which is in excess.
After cooling, the volume of the gases remaining was 90cm3
. Aqueous sodium hydroxide
was added to remove carbon dioxide, 30 cm3
of oxygen remained. All volumes were
measured at r.t.p..
(i) Explain why it is essential to use excess oxygen.
....................................................................................................................................
.............................................................................................................................. [2]
(ii) Carbon dioxide is slightly soluble in water. Why does it dissolve readily in the alkali,
sodium hydroxide?
.............................................................................................................................. [1]
(iii) Complete the following.
volume of gaseous hydrocarbon = ...............cm3
volume of oxygen used = .............cm3
volume of carbon dioxide formed = .............cm3
[2]
(iv) Use the above volume ratio to fi nd the mole ratio in the equation below and hence
fi nd the formula of the hydrocarbon.
........CxHy(g) + ........O2(g) → ........CO2(g) +........H2O(l)
hydrocarbon formula = ................................................ [2]