(a)(i) What is meant by cracking of petroleum fractions?
(ii) Write an equation for the laboratory preparation of ethene from ethanol.
(iii) Give one chemical test to distinguish between ethane and ethene.
(b)(i) Name the class of carbohydrates to which starch and cellulose belong.
(ii) What process is used for isolating ethanol from the other products of fermentation of sugar?
(iii) Name the organic product of the reaction between ethanol and sodium
(iv). Write the structural formula of 2-chloroethanol.
(c) State the reason why:
(i) benzene produces more soot than ethene on burning in excess air;
(ii) ethanoic acid has a higher boiling point than methanoic acid;
(iii) sodium chloride is used during the manufacture of soap.
(d) Give one use of: (i) ethyne (ii) coal (iii) carbon black
(a)(i) Cracking is the breaking down of large, long-chain hydrocarbon molecules from heavier petroleum fractions into smaller, more useful molecules (such as petrol and alkenes) using heat and/or a catalyst.
(ii) C2H5OH → C2H4 + H2O (heated with concentrated H2SO4 at about 170°C).
(iii) Add bromine water: ethene rapidly decolourizes the red-brown bromine water, while ethane does not.
(b)(i) Starch and cellulose are polysaccharides. (ii) Ethanol is isolated by fractional distillation. (iii) The organic product of ethanol + sodium is sodium ethoxide (C2H5ONa). (iv) 2-chloroethanol: ClCH2CH2OH.
(c)(i) Benzene produces more soot because it has a higher proportion of carbon (high carbon-to-hydrogen ratio), so it undergoes more incomplete combustion, releasing unburnt carbon. (ii) Ethanoic acid has a higher relative molecular mass and larger molecule than methanoic acid, giving stronger van der Waals forces (in addition to hydrogen bonding), so more energy is needed to boil it. (iii) Sodium chloride is added to precipitate (salt out) the soap, separating it from the glycerol and water.
(d)(i) Ethyne: oxy-acetylene welding/cutting. (ii) Coal: as a fuel (and a source of coke and coal tar). (iii) Carbon black: as a reinforcing filler in motor tyres (and a pigment in ink).
(a)(i) Cracking is the breaking down of large, long-chain hydrocarbon molecules from heavier petroleum fractions into smaller, more useful molecules (such as petrol and alkenes) using heat and/or a catalyst.
(ii) C2H5OH → C2H4 + H2O (heated with concentrated H2SO4 at about 170°C).
(iii) Add bromine water: ethene rapidly decolourizes the red-brown bromine water, while ethane does not.
(b)(i) Starch and cellulose are polysaccharides. (ii) Ethanol is isolated by fractional distillation. (iii) The organic product of ethanol + sodium is sodium ethoxide (C2H5ONa). (iv) 2-chloroethanol: ClCH2CH2OH.
(c)(i) Benzene produces more soot because it has a higher proportion of carbon (high carbon-to-hydrogen ratio), so it undergoes more incomplete combustion, releasing unburnt carbon. (ii) Ethanoic acid has a higher relative molecular mass and larger molecule than methanoic acid, giving stronger van der Waals forces (in addition to hydrogen bonding), so more energy is needed to boil it. (iii) Sodium chloride is added to precipitate (salt out) the soap, separating it from the glycerol and water.
(d)(i) Ethyne: oxy-acetylene welding/cutting. (ii) Coal: as a fuel (and a source of coke and coal tar). (iii) Carbon black: as a reinforcing filler in motor tyres (and a pigment in ink).
