(a)(i) Give one major use of alkenes.
(ii) Name the simplest alkane that exhibits structural isomerism
(iii) Determine the molar mass of an alkane that is represented as C\(_x\)F\(_{22}\). [H = 1, C = 12]
(iv) List two types of chemical reactions which the alkenes and alkynes undergo.
(b)(i) State the type of reaction involved in the conversion of palm oil to margarine.
(ii) Give the reason why the palm oil for manufacturing margarine is first treated activated charcoal
(iii) What is commonly used to catalyse the conversion of vegetable oils to margarine?
(c)(i) Name the class of organic compounds to which oils belong.
(ii) Describe briefly procedure for the manufacture of soap from vegetable oils
(iii) Explain why the presence of calcium ions in domestic water supply wastes soap.
(a)(i) One major use of alkenes: they are used in the manufacture of plastics/polymers (for example ethene is polymerized to polyethene). Ethene is also used to ripen fruits and to make ethanol.
(ii) The simplest alkane that exhibits structural isomerism is butane, \(C_4H_{10}\) (it exists as n-butane and 2-methylpropane).
(iii) For an alkane \(C_xH_{22}\), the general formula is \(C_nH_{2n+2}\):
\[2n + 2 = 22 \;\Rightarrow\; n = 10\]
So the alkane is \(C_{10}H_{22}\) (decane). Molar mass:
\[= (10 \times 12) + (22 \times 1) = 120 + 22 = 142\,g\,mol^{-1}\]
(iv) Two types of reaction that alkenes and alkynes undergo: addition reactions and polymerization (oxidation is also acceptable).
(b)(i) The conversion of palm oil to margarine is an addition reaction (specifically hydrogenation, the addition of hydrogen across the C=C double bonds).
(ii) The palm oil is first treated with activated charcoal in order to adsorb and remove the coloured impurities, i.e. to bleach/decolourize the oil.
(iii) The catalyst commonly used to convert vegetable oils to margarine is finely divided nickel.
(c)(i) Oils belong to the class of organic compounds called esters (specifically esters of glycerol and long-chain alkanoic (fatty) acids, i.e. lipids).
(ii) Manufacture of soap (saponification): the vegetable oil is boiled with concentrated sodium hydroxide solution; the oil is hydrolysed into soap (sodium salt of the fatty acid) and glycerol. Common salt (sodium chloride) is then added to \"salt out\" the soap, which rises to the surface as a solid, is skimmed off, washed and moulded.
(iii) Calcium ions in domestic water waste soap because they react with the soap (the sodium salt of the fatty acid) to form an insoluble scum (the calcium salt of the fatty acid). This scum forms before the soap can lather, so extra soap must be used before a lather is obtained.
(a)(i) One major use of alkenes: they are used in the manufacture of plastics/polymers (for example ethene is polymerized to polyethene). Ethene is also used to ripen fruits and to make ethanol.
(ii) The simplest alkane that exhibits structural isomerism is butane, \(C_4H_{10}\) (it exists as n-butane and 2-methylpropane).
(iii) For an alkane \(C_xH_{22}\), the general formula is \(C_nH_{2n+2}\):
\[2n + 2 = 22 \;\Rightarrow\; n = 10\]
So the alkane is \(C_{10}H_{22}\) (decane). Molar mass:
\[= (10 \times 12) + (22 \times 1) = 120 + 22 = 142\,g\,mol^{-1}\]
(iv) Two types of reaction that alkenes and alkynes undergo: addition reactions and polymerization (oxidation is also acceptable).
(b)(i) The conversion of palm oil to margarine is an addition reaction (specifically hydrogenation, the addition of hydrogen across the C=C double bonds).
(ii) The palm oil is first treated with activated charcoal in order to adsorb and remove the coloured impurities, i.e. to bleach/decolourize the oil.
(iii) The catalyst commonly used to convert vegetable oils to margarine is finely divided nickel.
(c)(i) Oils belong to the class of organic compounds called esters (specifically esters of glycerol and long-chain alkanoic (fatty) acids, i.e. lipids).
(ii) Manufacture of soap (saponification): the vegetable oil is boiled with concentrated sodium hydroxide solution; the oil is hydrolysed into soap (sodium salt of the fatty acid) and glycerol. Common salt (sodium chloride) is then added to \"salt out\" the soap, which rises to the surface as a solid, is skimmed off, washed and moulded.
(iii) Calcium ions in domestic water waste soap because they react with the soap (the sodium salt of the fatty acid) to form an insoluble scum (the calcium salt of the fatty acid). This scum forms before the soap can lather, so extra soap must be used before a lather is obtained.
