Question

CHEMISTRY

(a) A list of compounds is shown.
aluminium oxide
calcium bromide
calcium oxide
ethane
ethene
hydrogen chloride
methane
nitrogen dioxide
potassium iodide
potassium manganate(VII)
sodium chloride
Answer the following questions using only the compounds in the list.
Each compound may be used once, more than once or not at all.
Which compound:
(i) when in acidified solution, is used to test for sulfur dioxide
[1]
(ii) is the main constituent of natural gas
[1]
(iii) when dissolved in water, gives a yellow precipitate on addition of acidified aqueous
silver nitrate
.... [1]
(iv) is used in flue gas desulfurisation to neutralise acidic gases
(1)
(v) is a reactant used in the manufacture of ethanol?
[1]
(b) What is the meaning of the term compound?
[2]​

Answer 1

1.The solution will gradually become colorless as the sulfur dioxide reacts with the potassium permanganate(Potassium manganate(VII))

The reaction

2MnO₄⁻ (aq) + 6H⁺ (aq) + 5SO₃²⁻ (aq) -> 2Mn²⁺ (aq) + 3H₂O (l) + 5SO₄²⁻ (aq)

2. Natural gas is a mixture of hydrocarbon gas with methane (CH₄) as the main composition in addition to other gases such as CO₂ and H₂

3. Halide ions are detected using silver nitrate (acidified using nitric acid) which forms deposits of different colors

Br-Bromide ions: cream

Cl-Chloride ions: white

I-Iodide ions: yellow

so the answer Potassium iodide

4. Compounds that are alkaline are useful for neutralizing acids including the desulfurization process to neutralize acidic gases (SO₃). The bases used are lime or caustic soda

Lime can be Calcium oxide (CaO - quicklime)

5. Ethanol (C₂H₅OH) can be made from C₂H₄ (ethene) with steam, apart from the Alcoholic fermentation of glucose

6. Compounds are formed from 2 or more types of elements which can be ionic compounds or covalent compounds