(a)(i) What is isomerism? (ii) Name the alkanol that is isomeric with methoxymethane (CH\(_3\)OCH\(_3\)). (b)(i) Outline the laboratory:preparation of ethyl...
Question 1 Report
(a)(i) What is isomerism?
(ii) Name the alkanol that is isomeric with methoxymethane (CH\(_3\)OCH\(_3\)).
(b)(i) Outline the laboratory:preparation of ethylethanoate. (Diagrams not required)
(ii) Write the structural formula of ethylethancqte
(iii) State two physical properties of ethylethanoate.
(c) When gas oil which consists of larger hydrocarbons was subjected to high temperature and pressure, the following reaction occurred.
C\(_{17}\)H\(_{36(l)}\) \(\to\) 3C\(_2\)H\(_{4(g)}\) + C\(_3\)H\(_{6(g)}\) + Q\(_{(l)}\)
(i) What name is given to the process indicated above?
(ii) State the importance of the process to the petroleum industry.
(iii) Find the formula of the product which Q represents in the equation above.
(iv) Mention one type of chemical industry that utilizes ethene as raw material.
(d) Consider the following compounds: CH\(_3\) — (CH\(_2\))\(_2\) —CH\(_3\); C\(_6\)H\(_5\) —CH = CH\(_2\); CH=C — CH\(_3\). State which of them:
(i) is used as a domestic fuel;
(ii) is an aromatic compound,
(iii) participates in such situation but not addition reactions;
(iv) would react with two moles of hydrogen per mole.
Answer Details
(a)(i) Isomerism is the existence of two or more compounds having the same molecular formula but different structural arrangements of their atoms (and hence different properties).
(a)(ii) Methoxymethane \(CH_3OCH_3\) has molecular formula \(C_2H_6O\). The isomeric alkanol is ethanol, \(C_2H_5OH\).
(b)(i) Laboratory preparation of ethyl ethanoate
- Warm a mixture of ethanoic acid and ethanol together with a little concentrated tetraoxosulphate(VI) acid (which acts as catalyst and dehydrating agent) under reflux.
- Esterification occurs: \[CH_3COOH + C_2H_5OH \underset{\Delta}{\overset{H_2SO_4}{\rightleftharpoons}} CH_3COOC_2H_5 + H_2O\]
- Distil off the ester and purify it by shaking with sodium trioxocarbonate(IV) solution (to remove acid) followed by drying and redistillation.
(b)(ii) Structural formula: \(CH_3-CO-O-CH_2-CH_3\) (i.e. \(CH_3COOC_2H_5\)).
(b)(iii) Two physical properties: it is a colourless liquid with a sweet, fruity smell; it is only slightly soluble in water but volatile.
(c) \(C_{17}H_{36} \to 3C_2H_4 + C_3H_6 + Q\)
- (i) The process is cracking (thermal/catalytic cracking).
- (ii) It is important because it breaks large, less useful hydrocarbon molecules into smaller, more useful ones (petrol and gaseous alkenes), increasing the yield of petrol and supplying alkenes as raw materials.
- (iii) Balancing carbon: \(17 = (3\times2) + 3 + C_Q \Rightarrow C_Q = 8\). Balancing hydrogen: \(36 = (3\times4) + 6 + H_Q \Rightarrow H_Q = 18\). Therefore Q is \(C_8H_{18}\) (octane).
- (iv) The plastics (polymer) industry, which polymerises ethene to poly(ethene). The manufacture of ethanol is also acceptable.
(d) The compounds are butane \(CH_3(CH_2)_2CH_3\), phenylethene \(C_6H_5CH=CH_2\), and propyne \(CH\equiv C-CH_3\).
- (i) Domestic fuel: butane, \(CH_3(CH_2)_2CH_3\).
- (ii) Aromatic compound: phenylethene (styrene), \(C_6H_5CH=CH_2\).
- (iii) Undergoes substitution but not addition: butane (a saturated alkane).
- (iv) Reacts with two moles of hydrogen per mole: propyne, \(CH\equiv C-CH_3\) (the triple bond adds \(2H_2\)).
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