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Question 3
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- A colourless gas P was given off when dilute tetraoxosulphate (VI) acid was added to zinc salt Q. On bubbling the gas through lime water, a white precipitate R was formed. Identify P, Q and R.
- Name a suitable apparatus that could be used to perform each of the following activities in the laboratory:
i. storage of dilute silver trioxonitrate (V);
ii. heating copper metal;
iii. separation of a mixture of water and kerosine.
Give one reason for each of your answers in (b).
Most candidates were unable to make precise statements. Most candidates correctly identifiedPas CO2 and R as CaCO3 but could not identify Q as ZnCO3. Most candidates could neither name nor give correct reason for a suitalbe apparatus for:
- storing of dilute silver trioxonitrate (V);
- heating copper metal.
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Many candidates however, correctly named the separating funnel and gave correct reason for using it.
The expected answers are:
- P – CO2 or Carbon(IV) oxide
Q - ZnCO3 or Zinc trioxocarbonate (IV)
R – CaCO3 or calcium trioxocarbonate (IV)
- (i) - dark brown/amber coloured bottle
(ii) - bunsen burner
(iii) - separating funnel
Reason
- Amber coloured bottle reduces the intensity of/prevents light entering the bottle to decompose Ag NO3.
- Bunsen burner produces high intensity of heat/tempearture
- Because water and kerosene are not miscible/due to immiscibility of water and kerosene.
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