(a)(i) Define the term polymerization.
(ii) List the three conditions required for the polymerization on of ethene.
(iii) State the property which is common to compounds that can be easily polymerized
(b) Write appropriate equations to show how the following can be obtained from propan-1-ol in the labouratory
(i) propene;
(ii) propylmethanoate. State the type of reaction involved in each case.
(c)(i) A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen. Determine its molecular formula if its molar mass is 180 (H = 1, C = 12, O = 16)
(ii) Explain why ethanoic acid boils at a much higher temperature than butane even though their molar masses almost equal.
(a)(i) Polymerization: the chemical process in which many small molecules (monomers) join together to form a very large molecule (a polymer).
(a)(ii) Conditions for polymerization of ethene: high pressure, high temperature (moderately raised temperature), and a catalyst (e.g. a trace of oxygen or a Ziegler-Natta catalyst).
(a)(iii) The common property is that such compounds are unsaturated (they contain a carbon-carbon double bond, C=C).
(b) From propan-1-ol (CH3CH2CH2OH):
- (i) Propene, by dehydration with concentrated H2SO4 (or hot Al2O3): \(\text{CH}_3\text{CH}_2\text{CH}_2\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \text{CH}_3\text{CH}=\text{CH}_2 + \text{H}_2\text{O}\). Type: elimination (dehydration).
- (ii) Propyl methanoate, by esterification with methanoic acid: \(\text{HCOOH} + \text{C}_3\text{H}_7\text{OH} \rightleftharpoons \text{HCOOC}_3\text{H}_7 + \text{H}_2\text{O}\). Type: esterification (condensation).
(c)(i) Molecular formula from 40.0% C, 6.7% H, 53.3% O:
| Element | %/Ar | ratio |
|---|
| C | 40.0/12 = 3.33 | 1 |
| H | 6.7/1 = 6.7 | 2 |
| O | 53.3/16 = 3.33 | 1 |
Empirical formula = CH2O (mass = 30). \(n = \dfrac{180}{30} = 6\), so the molecular formula is C6H12O6.
(c)(ii) Ethanoic acid molecules contain O-H groups and form strong intermolecular hydrogen bonds (indeed dimers) between molecules, whereas butane, being non-polar, has only weak van der Waals forces. Much more energy is needed to overcome the hydrogen bonds, so ethanoic acid boils at a much higher temperature despite the similar molar mass.
(a)(i) Polymerization: the chemical process in which many small molecules (monomers) join together to form a very large molecule (a polymer).
(a)(ii) Conditions for polymerization of ethene: high pressure, high temperature (moderately raised temperature), and a catalyst (e.g. a trace of oxygen or a Ziegler-Natta catalyst).
(a)(iii) The common property is that such compounds are unsaturated (they contain a carbon-carbon double bond, C=C).
(b) From propan-1-ol (CH3CH2CH2OH):
- (i) Propene, by dehydration with concentrated H2SO4 (or hot Al2O3): \(\text{CH}_3\text{CH}_2\text{CH}_2\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4} \text{CH}_3\text{CH}=\text{CH}_2 + \text{H}_2\text{O}\). Type: elimination (dehydration).
- (ii) Propyl methanoate, by esterification with methanoic acid: \(\text{HCOOH} + \text{C}_3\text{H}_7\text{OH} \rightleftharpoons \text{HCOOC}_3\text{H}_7 + \text{H}_2\text{O}\). Type: esterification (condensation).
(c)(i) Molecular formula from 40.0% C, 6.7% H, 53.3% O:
| Element | %/Ar | ratio |
|---|
| C | 40.0/12 = 3.33 | 1 |
| H | 6.7/1 = 6.7 | 2 |
| O | 53.3/16 = 3.33 | 1 |
Empirical formula = CH2O (mass = 30). \(n = \dfrac{180}{30} = 6\), so the molecular formula is C6H12O6.
(c)(ii) Ethanoic acid molecules contain O-H groups and form strong intermolecular hydrogen bonds (indeed dimers) between molecules, whereas butane, being non-polar, has only weak van der Waals forces. Much more energy is needed to overcome the hydrogen bonds, so ethanoic acid boils at a much higher temperature despite the similar molar mass.
