2022 NTSS Chemistry P3

1 This document consists of 18 printed pages. Setter: Ms Caley Ng NEW TOWN SECONDARY SCHOOL Preliminary Examination Secondary 4 Express / 5 Normal (Academic) NAME CLASS INDEX NUMBER Science (Chemistry) Paper 3 Chemistry Candidates answer on the Question Paper. No Additional Materials are required. 5076/03, 5078/03 19 August 2022 1 hour 15 minutes 1100 – 1215 READ THESE INSTRUCTIONS FIRST Write your name, register number and class in the spaces provided above. You may use an HB pencil for any diagrams, graphs, tables or rough working. Write in dark blue or black pen. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. Section A (45 marks) Answer all questions. Write your answers in the spaces provided on the question paper. For Examiner’s Use Paper 1 Paper 3 Section A Paper 3 Section B Q___ Q___ Total Section B (20 marks) Answer any two questions. Write your answers in the spaces provided on the question Paper. A copy of the Data Sheet is printed on page 17. A copy of the Periodic Table is printed on page 18. The number of marks is given in brackets [ ] at the end of each question or part question.

2 Section A (45 marks) Answer all the questions in the spaces provided. 1 Choose from the following substances to answer the questions. nitrogen dioxide argon calcium hydroxide carbon monoxide oxygen lithium oxide sodium hydroxide zinc oxide Each substance may be used once, more than once or not at all. Identify the substance which (a) contributes to acid rain ……………………………………………………………………………………… [1] (b) is used to control pH in soils ……………………………………………………………………………………… [1] (c) reacts with both acids and bases ……………………………………………………………………………………… [1] (d) is used to fill tungsten bulbs ……………………………………………………………………………………… [1] [Total: 4]

3 2 24Mg, 25Mg and 26Mg are isotopes of magnesium. (a) Define isotopes. ……………………………………………………………………………………………. ………………………………………………………………………………………… [1] (b) Complete Table 2.1 to describe the structure of a magnesium atom and a magnesium ion. Table 2.1 number of protons neutrons electrons a 24Mg atom 12 a 25Mg ion 10 [4] (c) A student made the following claim: “The chemical formula for magnesium chloride is MgCl2, no matter which isotope is used.” With reference to the electronic configuration of magnesium, explain if you agree with the student. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………….…... [2] [Total: 7]

4 3 In the early 1800’s, Friedrich Wöhler, a German chemist, first isolated beryllium metal. The chemical equation for the reaction he used to isolate beryllium metal from beryllium chloride is: BeCl2 (s) + 2K (s) → 2KCl (s) + Be (s) (a) Explain, in terms of oxidation states, whether this reaction is considered a redox reaction. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………….….. [2] (b) Wöhler had to ensure that the reaction vessel containing potassium was dry before reacting with beryllium chloride. Explain why the reaction vessel has to be kept dry. ……………………………………………………………………………………………. ………………………………………………………………………………………… [1] [Total: 3] 4 Carbon monoxide is one of the common air pollutants in the atmosphere. (a) Describe and explain the harmful effect of carbon monoxide on human. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………….….. [2]

5 (b) Carbon monoxide burns in oxygen to form carbon dioxide as shown: 2CO (g) + O2 (g) → 2CO2 (g) Calculate the volume of oxygen required to burn 0.14 g of carbon monoxide. [Relative atomic masses: Ar: C, 12; O, 16] volume of oxygen required = ………………………… [3] (c) Draw a ‘dot and cross’ diagram to show the arrangement of the outer shell electrons in a molecule of carbon dioxide. [Proton numbers: C, 6; O, 8] [2] (d) Explain, with reference to the structure and bonding, why carbon dioxide has a low boiling point. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………….….. [2] [Total: 9]

6 5 A group of students have written out instructions for the preparation of a pure, dry sample of copper(II) sulfate crystals. They have made several mistakes. Read their instructions and complete Table 5.1 with three of their mistakes and corrections of these mistakes. Table 5.1 students’ mistake corrections to mistake [3] [Total: 3] Student-written instructions to prepare pure, dry copper(II) sulfate crystals. 1. Wear safety goggles and gloves. 2. Warm copper powder with dilute sulfuric acid to form a solution of copper(II) sulfate, CuSO4. 3. Filter the mixture to remove any unreacted solids. 4. Heat the filtrate until most of the solvent has evaporated. Leave to cool. 5. Separate the crystals by filtering. 6. Rinse the crystals with large amounts of cold water. 7. Press dry the crystals with filter paper.

7 6 A student did an experiment to investigate the factors that affect the rate of the following reaction. 2HCl (aq) + Mg (s) → MgCl2 (aq) + H2 (g) Dilute hydrochloric acid at room temperature was placed in a flask on a weighing balance. Excess powdered magnesium was added to the acid. The total mass of the flask and its contents was recorded at fixed time intervals. The results of his experiment is shown in Fig. 6.1. Fig. 6.1 (a) The student repeated the above experiment using the same mass of magnesium strip instead of powder. Add to Fig. 6.1 the graph you would expect. Label as graph (a). [2] (b) Use your knowledge of reacting particles to explain the effect of increasing the temperature of the reaction mixture on the rate of the reaction. ……………………………………………………………………………………………. ……………………………………………………………………………………………. ……………………………………………………………………………………………. …………………………………………………………………………………….….. [3] time total mass of flask and contents

8 (c) Describe a chemical test and observation for the gas given off during this chemical reaction. test: ….…………………………………………………………………….……………… observation: ….………………………………………………………………………..… ……………………………………………………………………………………….... [2] (d) Another student conducted a similar experiment. Instead of using magnesium powder, the student replaced it with zinc powder to react with the same volume and concentration of dilute hydrochloric acid at room temperature. Describe the difference in the rate of reaction, if any. ……………………………………………………………………….……………...… [1] [Total: 8]

9 7 Fig. 7.1 describes some of the substances that result from the chemical reactions of an aqueous solution of salt K. Fig. 7.1 (a) Identify each of K, L, M and N. K ……………………………………….. L ………………………………………. M ……………………………………….. N ……………………………………….. [4] (b) Write a balanced chemical equation for any one of the reactions in Fig. 7.1. ……………………………………………………………………………………….. [2] [Total: 6] add acidified, aqueous barium nitrate

10 8 (a) Organic compounds are placed in an homologous series. Give two general properties of an homologous series. …………………………………………………………………………………………… …………………………………………………………………………………………… …………………………………………………………………………………….….. [2] (b) The structure of an organic compound, X, is shown below. In a molecule of X, there are two different functional groups. Circle and label the functional group that would react with aqueous sodium hydroxide.