(a) A compound of carbon, hydrogen and chlorine contains 0.48 g of carbon, 0.08 g of hydrogen and 1.42 g of chlorine. (i) Determine the empirical formula of...
Question 1 Report
(a) A compound of carbon, hydrogen and chlorine contains 0.48 g of carbon, 0.08 g of hydrogen and 1.42 g of chlorine.
(i) Determine the empirical formula of the compound.
(ii) If the molar mass of the compound is 99, calculate the molecular formula of the compound.
[H = 1.0, C = 12.0, Cl = 35.5]
(b) State three properties of NaCl (s) which shows that it is ionic.
(c) Consider the following reaction equation:
(i) On the same diagram, sketch and label a reaction profile for a catalysed and uncatalysed reaction between \(H_2\) and \(O_2\).
(ii) Indicate the possible positions of the activated complexes for the reaction profiles in (c)(i).
(d) The petrochemical industry produces addition polymers using one of the fractions obtained from crude oil.
(i) Name the fraction used as a raw material for the process.
(ii) What process is used to obtain the fraction from crude oil?
(iii) Name two gaseous hydrocarbons that can be used in making polymers.
(iv) Describe briefly how these hydrocarbons can be obtained.
(v) Name the polymer produced from one of the hydrocarbons named in (d)(iii).
Answer Details
(a) (i) Empirical formula
| Element | Mass/g | Moles | Simplest ratio |
|---|---|---|---|
| C | 0.48 | \(\frac{0.48}{12}=0.04\) | \(\frac{0.04}{0.04}=1\) |
| H | 0.08 | \(\frac{0.08}{1}=0.08\) | \(\frac{0.08}{0.04}=2\) |
| Cl | 1.42 | \(\frac{1.42}{35.5}=0.04\) | \(\frac{0.04}{0.04}=1\) |
Ratio of atoms \(=1:2:1\).
Empirical formula \(=\boxed{\mathrm{CH_2Cl}}\).
(a) (ii) Molecular formula
Empirical formula mass \(=12+2(1)+35.5=49.5\).
\[n=\frac{99}{49.5}=2\]
Molecular formula \(=(\mathrm{CH_2Cl})_2=\boxed{\mathrm{C_2H_4Cl_2}}\).
(b) Properties of sodium chloride showing that it is ionic
- It has high melting and boiling points because of strong electrostatic forces between oppositely charged ions.
- Solid sodium chloride does not conduct electricity, but molten sodium chloride and aqueous sodium chloride conduct electricity because their ions are mobile.
- It is readily soluble in water, a polar solvent.
(c) (i) and (ii) Reaction profiles for the reaction between hydrogen and oxygen
The activated complexes are at the tops of the respective curves, as labelled. The catalysed route has a lower activation energy than the uncatalysed route.
(d)
(i) The fraction used as raw material is naphtha.
(ii) It is obtained from crude oil by fractional distillation.
(iii) Two gaseous hydrocarbons used in making polymers are ethene and propene.
(iv) They are obtained by cracking long-chain hydrocarbons in fractions such as naphtha. In catalytic cracking, the hydrocarbon vapour is heated to about \(600^\circ\mathrm{C}\) over a silica/alumina catalyst, producing smaller molecules including alkenes.
(v) Ethene produces poly(ethene) or polythene. Propene produces poly(propene).
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