HKCEE Chemistry Past Paper fossil fuels
CE : Section 5 Fossil Fuels
1. 93 1(c) Alkenes can be obtained from petroleum fractions by a process called 'cracking’. Using a suitable petroleum fraction, a student carried out this process in the laboratory and collected the gaseous product over water. (i) What is 'cracking’ ? (ii) Draw a labelled diagram of a laboratory set-up that can be used for carrying out the process and collecting the gaseous product. (iii) An important safety precaution in the experiment is to prevent sucking back. (1) What is the potential hazard if sucking back occurs ? (2) How can sucking back be prevented ? (iv) If the gaseous product decolorizes a solution of bromine in tetrachloromethane, can you conclude that the gaseous product in ethene ? Explain your answer. (8 marks)
2. 93 3(b)(iii) When chemical wastes such as methylbenzene and tetrachloromethane are burnt in the incinerator in the plant, several pollutants including sulphur dioxide are produced. (1) Explain why sulphur dioxide is emitted from the incinerator. (2) Name TWO pollutants other than sulphur dioxide which are emitted from the incinerator and state ONE harmful effect for each pollutant.
(5 marks)
3. 94 6(a) The following experimental set-up was used to determine the empirical formula of an oxide of copper.
In the experiment, 8.58 g of an oxide of copper, after complete reaction, produced 7.62 g of copper. (i)* Deduce the empirical formula of the oxide of copper. (ii) Write an equation for the reaction that occurred in the combustion tube. (iii) State TWO potential hazards associated with this experiment, and suggest a safety precaution for each hazard. (iv) At the end of the reaction, heating was stopped. However, it was necessary to continue passing the town gas through the combustion tube until the tube had cooled down. Explain why. (Relative atomic masses : Cu = 63.5, O = 16.0)
(8 marks)
4. 95 8(a) The fumes emitted from a factory using diesel fuel contain several
1. 93 1(c) Alkenes can be obtained from petroleum fractions by a process called 'cracking’. Using a suitable petroleum fraction, a student carried out this process in the laboratory and collected the gaseous product over water. (i) What is 'cracking’ ? (ii) Draw a labelled diagram of a laboratory set-up that can be used for carrying out the process and collecting the gaseous product. (iii) An important safety precaution in the experiment is to prevent sucking back. (1) What is the potential hazard if sucking back occurs ? (2) How can sucking back be prevented ? (iv) If the gaseous product decolorizes a solution of bromine in tetrachloromethane, can you conclude that the gaseous product in ethene ? Explain your answer. (8 marks)
2. 93 3(b)(iii) When chemical wastes such as methylbenzene and tetrachloromethane are burnt in the incinerator in the plant, several pollutants including sulphur dioxide are produced. (1) Explain why sulphur dioxide is emitted from the incinerator. (2) Name TWO pollutants other than sulphur dioxide which are emitted from the incinerator and state ONE harmful effect for each pollutant.
(5 marks)
3. 94 6(a) The following experimental set-up was used to determine the empirical formula of an oxide of copper.
In the experiment, 8.58 g of an oxide of copper, after complete reaction, produced 7.62 g of copper. (i)* Deduce the empirical formula of the oxide of copper. (ii) Write an equation for the reaction that occurred in the combustion tube. (iii) State TWO potential hazards associated with this experiment, and suggest a safety precaution for each hazard. (iv) At the end of the reaction, heating was stopped. However, it was necessary to continue passing the town gas through the combustion tube until the tube had cooled down. Explain why. (Relative atomic masses : Cu = 63.5, O = 16.0)
(8 marks)
4. 95 8(a) The fumes emitted from a factory using diesel fuel contain several