2022 Peirce Chemistry P3

1 [Turn over Class Register No. Candidate Name PEIRCE SECONDARY SCHOOL PRELIMINARY EXAMINATION 2022 SECONDARY 4 EXPRESS / 5 NORMAL ACADEMIC SCIENCE (CHEMISTRY) 5076/03, 5078/03 Paper 3 (Theory) 26 AUGUST 2022 1 hour 15 minutes Candidates answer on the Question Paper. Additional Materials: Periodic Table INSTRUCTIONS TO CANDIDATES Write your name, class and register number on all the work you hand in. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Section A Answer all questions in the spaces provided. Section B Answer any 2 questions. Answer all questions in the spaces provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. A copy of Data Sheet is printed on page 17. The use of an approved scientific calculator is expected, where appropriate. For Examiners’ Use Section A Parent’s signature Section B Total This paper consists of 17 printed pages and 1 blank page. Setter: Miss Pang Yin Yin

2 [Turn over Section A Answer all questions in this section in the spaces provided. The total marks for this section is 45. 1 A teacher used food (coloured candy) to demonstrate a science concept taught during the topic on separation technique. He spotted the colour obtained from the sample candy onto the paper and 3 permitted food dyes (PD1, PD2, PD3) are used for comparison. He estimated the height of the solvent and placed the paper into a beaker of solvent and allowed separation to take place. Fig. 1.1 shows the results after separation is completed. Fig. 1.1 (a) State the separation technique demonstrated by the teacher. …………………………………………………………………………………………. [1] (b) Draw a line on Fig. 1.1 to indicate the “height of the solvent when the paper is placed in the beaker”. Label it as (b). [1] (c) Is the candy safe for consumption? Explain your answer. …………………………………………………………………………………………. …………………………………………………………………………………………. [1] (d) Suggest one other use of chromatography. …………………………………………………………………………………………. [1] [Total:4]

3 [Turn over 2 Fig. 2.1 shows some properties and reactions of aqueous ammonia and some other substances. Fig. 2.1 Suggest the identity of A, B, C and D. A ………………………………………………………………………………………. [1] B ………………………………………………………………………………………. [1] C ………………………………………………………………………………………. [1] D ………………………………………………………………………………………. [1] [Total:4] Colourless acid solution A White precipitate B Add aqueous barium nitrate White salt C Colourless gas D Add aqueous sodium hydroxide,warm Add aqueous ammonia

4 [Turn over 3 In Fig. 3.1, A-F represent particles in different substances. Fig. 3.1 Which one of A-F best represents (a) pure carbon dioxide ……………………… [1] (b) pure oxygen ……………………… [1] (c) a mixture of compounds ……………………… [1] (d) a mixture of elements ……………………… [1] (e) the products of complete combustion of hydrocarbons? ……………………… [1] [Total:5]

5 [Turn over 4 (a) Most elements occur naturally as a mixture of isotopes. For example, magnesium consists of 5 isotopes but the more stable ones are 24Mg, 25Mg and 26Mg. Complete the table for isotope 25Mg. Number of protons Number of neutrons Number of electrons [2] (b) All magnesium compounds have good electrical conductivity in molten states due to presence of mobile ions. (i) Name the type of chemical bonding present in magnesium oxide. …………………………………………………………………………………… [1] (ii) Draw a ‘dot and cross’ diagram to show the arrangement of electrons in magnesium oxide in the space below. Show only valence electrons. [ Atomic number: Mg,12; O,8] [2] [Total:5]

6 [Turn over 5 (a) A solution of nitric acid, HNO3, has a concentration of 126 g/dm3. (i) Calculate the relative molecular mass of nitric acid. [Relative atomic masses: Ar: H,1;N,14;O,16] Relative molecular mass : …………………….. [1] (ii) Calculate the concentration of the solution in mol/dm3. Concentration: ………… mol/dm3 [1] (b) Magnesium carbonate reacts with nitric acid as follows: MgCO3 + 2HNO3 → Mg(NO3)2 + H2O + CO2 How many moles of magnesium carbonate are needed to react with 1.0 mol of nitric acid? Number of moles of magnesium carbonate: ………………. mol [1] [Total:3]

7 [Turn over 6 (a) Dilute acids have many reactions with metals, carbonates and bases. For example, dilute sulfuric acid reacts with calcium carbonate to form a gas, water and an insoluble salt. The same acid reacts with calcium oxide to form water and an insoluble salt. (i) Write an equation for either one of the reactions mentioned above. Include state symbols. …………………………………………………………………………………... [2] (ii) Calcium sulfate can be obtained through mixing calcium nitrate and sodium sulfate solutions. Suggest how a pure dry sample of the calcium sulfate can be obtained from the reaction mixture. …………………………………………………………………………………... …………………………………………………………………………………... ………………………………………………………………………………….. [3] (b) Sulfuric acid also participates in redox reactions. In each of these redox equations with sulfuric acid, using change in oxidation states, identify the substance being oxidised / reduced and give a reason. (i) Fe + H2SO4 → FeSO4 + H2 Substance oxidised: ………………………………………………………….. Reason: ………………………………………………………………………... [2] (ii) C + 2H2SO4 → CO2 + 2SO2 + 2H2O Substance reduced: ………………………………………………………….. Reason: ………………………………………………………………………... [2] [Total:9]

8 [Turn over 7 Table 7.1 shows the properties of some elements in Group VII. Table 7.1 element molecular formula electronic structure melting point / oC boiling point / oC radius of ion / pm chlorine Cl2 2.8.7 -101 -35 181 bromine Br2 2.8.18.7 -7 59 195 iodine I2 2.8.18.18.7 113 184 216 X 350 610 (1 pm = 1 x 10-12 m) (a) Which element in the table is a liquid at room temperature and pressure? …………………………………………………………………………………………. [1] (b) How many outer shell electrons does X have? …………………………………………………………………………………………. [1] (c) Predict the molecular formula of element X. …………………………………………………………………………………………. [1] (d) Estimate a value for the radius of X- ion. …………………………………………………………………………………………. [1] (e) Write the formula of the compound whe