HKCEE Chemistry 2007 Paper 1
1. A is a compound formed from oxygen and magnesium, while B is a compound formed from oxygen and fluorine. a) Draw the electronic diagram of A, showing electrons in he outermost shells only. (1)
b) Draw the electronic diagram of B, showing electrons in the outermost shells only. (1)
c) Compare the melting points of A and B. Explains your answer. Melting point of A is higher than that of B.
Ions of A are linked by strong ionic bonds / electrostatic force forming giant crystal lattice. (1) Molecules of B are attracted by weak van der Waals’ forces / intermolecular forces. (1)
2. A student performed an experiment to crack paraffin oil and collect the gaseous products by using a boiling tube. a) Draw a labeled diagram to show how this experiment can be performed in the laboratory.
b) (i) The student added a few drops of bromine water into the boiling tube containing the gascous products. The brown colour of bromine water disappeared immediately. Why? The products of cracking contained unsaturated (hydrocarbons) / alkenes / C=C / ethane / reasonable name of alkene, which decolourised the bromine water immediately by addition reaction (2) (II) The student then dropped more bromine water into the boiling tube until the brown colour of the bromine water persisted. After about 10 minutes, the brown colour disappeared. Why? The products of cracking also contained saturated (hydrocarbons) / alkanes / methane/reasonable name or molecular formula of alkane, which decolourised the bromine water slowly by substitution reaction. (2)
3. The diagram below shows the set-up used in performing a microscale experiment. A drop of hydrochloric acid was added to the drop of chlorine bleach in a petri dish was immediately covered with is lid. Chlorine gas formed by the reaction between chlorine bleach and hydrochloric acid eventually filled up the whole set-up.
a) Write a chemical equation for the reaction between chlorine bleach and hydrochloric acid. (1)
b) State the expected observation at position C and position D. In each case, write a relevant chemical equation if a reaction occurred. i. Position C
Change (from colourless) to brown/yellow (1)
ii. Position D
No observable change/reaction (1)
c) Suggest one advantage of replacing test tube experiments with morescale experiments. Less chemicals are used / less harmful to environment / less dangerous / easy to handle / save money / save time (1)
4. A student learnt from a book that an ancient chemical cell could be made by immersing an iron rod in a liquid placed inside a copper can. The liquid used was vinegar but not wine. The diagram below shows the set-up designed by him in simulation the cell.
a) Explain, in terms of structure and property of particles why the liquid inside the ancient chemical cell was vinegar but not wine. Both vinegar and wine contain molecules. (1)
Only vinegar (ethanoic acid) can ionize in water / contains (mobile) ions for conducting electricity. (1) b) The student found that the iron rod dissolved gradually, and colourless gas bubbles were given out on the inner wall of the copper can. i. Write a half equation, involving iron, for the reaction that occurred at the iron rod. (1)
ii. Write a half equation for the reaction that occurred on the inner wall of the copper can. (1)
c) The student found that colourless gas bubbles were also given out at the surface of the iron rod that immersed in vinegar. Explain the observation. Iron reacts directly with vinegar/H+ (aq) giving out hydrogen gas. (1)
5. A solid sample contains zinc and copper only. The composition of the solid sample was analysed experimentally as outlined below: 2.00 g of the solid sample was added to excess dilute hydrochloric acid in a beaker. Upon completion of reaction, the mixture inside the beaker was filtered. The residue...
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