NYGH 2012-S3EOY-Chem P2

Class Register Number Name 南洋女子中学校 NANYANG GIRLS’ HIGH SCHOOL End-of-Year Examination 2012 Secondary Three CHEMISTRY 1 hour 45 minutes Paper 2 0915 to 1100 Thursday 11 October 2012 Additional materials: Writing papers READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name, register number and class in the spaces at the top of this page and on any separate answer paper used. Section A (40 marks) Answer all questions and write your answers in the spaces provided on the question paper. Please note that if you do not write your answers in the spaces provided specially for that purpose, that section of the paper will be awarded ZERO marks. Section B (30 marks) Answer all questions including questions 6, 7 and 8 Either or 8 Or. Write your answers on the separate writing paper provided. At the end of the examination, 1. fasten all your work securely together; 2. tick 8 Either (for Either) or 8 Or (for Or) in the grid below to indicate which question you have answered. INFORMATION FOR CANDIDATES Examiner’s Use Section A Section B 6 7 8 Either 8 Or Total The intended number of marks is given in the brackets [ ] at the end of each question or part question. You are advised to spend no longer than one hour on Section A and no longer than 45 minutes on Section B. Use of Scientific Calculator is allowed. A copy of the Periodic Table is found on page 12. Setters: ZJ/CW/ET This document consists of 12 printed pages. NANYANG GIRLS’ HIGH SCHOOL [Turn over

2012 End-of-Year Examination Secondary Three 2 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II Section A Answer all questions in the spaces provided. A1 The electronic configurations of the atoms of two elements, V and W, are listed below. V: 2. 5 W: 2. 8. 2 (a) Predict and explain which element, V or W, has a lower melting point. [3] (b) Another element R, in the same period as W, forms a compound with oxygen with the formula R2O. R2O is a gas at room temperature. (i) Predict whether R2O will conduct electricity in molten state. [1] (ii) Draw the ‘dot and cross’ diagram for the compound R2O. [2] (c) A new element U was discovered and two of its properties were listed below. 1. It forms a compound with V with the formula U 3V2. 2. U3V2 is a conductor of electricity in molten and aqueous state. (i) Suggest a suitable Group in the Periodic table to place the new element U. [1] [Total marks: 7]

2012 End- of-Year Examination Secondary Three 3 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II [Turn over (ii) State and explain whether element U is able to conduct electricity in the solid state. [2] A2 In the preparation of magnesium nitrate, a reaction was carried out by adding excess magnesium hydroxide solid to ensure all acid is used up. (a) Explain why magnesium hydroxide can be used in excess but not nitric acid. [2] (b) The hydrated product obtained has the formula Mg(NO3)2∙6H2O. (i) State the number of ions present in each unit of hydrated magnesium nitrate. [1] (ii) State the type(s) of bond(s) present in a unit of anhydrous magnesium nitrate. [1] [Total marks: 6]

2012 End-of-Year Examination Secondary Three 4 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II A3 (a) Student A decided to prepare a pure sample of potassium nitrate in the laboratory. He added 4.80 g of solid potassium carbonate to 24.00 cm 3 of 1.67 mol/dm 3 dilute nitric acid. The solution obtained was then filtered and the final product was obtained by crystallization of the filtrate. (i) Write a chemical equation with state symbols for this reaction [2] (ii) Show with calculation, the limiting reagent for the reaction. [2] (iii) The percentage yield of the above reaction was 170%. Calculate the mass of product collected by the student. [1] (iv) A significant amount of the excess reactant was present in the final product, thus resulting in a yield greater than 100%. Explain why the excess reactant was not removed during the experiment. [1] [Total marks: 6]

2012 End- of-Year Examination Secondary Three 5 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II [Turn over (b) Another student, B, wanted to prepare the same salt by titrating 30.00 cm3 of 0.400 mol/dm3 potassium hydroxide to 20.0 cm3 of dilute nitric acid. The solution obtained was then filtered and the final product was obtained by crystallization of the filtrate. (i) Write the ionic equation for this reaction. [1] (ii) Calculate the concentration of the dilute nitric acid used. [2] (c) State whether the method used by student A or B is more suitable for the preparation of a sample of pure dry potassium nitrate. [1] [Total marks: 4]

2012 End-of-Year Examination Secondary Three 6 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II A4 The strength of an acid is determined by the extent it dissociates in a given volume of water. The stronger an acid, a larger percentage of it will dissociate into ions when dissolved in water. Properties of two acids HA and H 2B were investigated. Assume that only acidic hydrogens are shown in the formula. (a) State the basicity of acid H2B. [1] (b) Both HA and H2B were dissolved in the 1.00 dm 3 of water separately. (i) When 3 moles of HA was dissolved, only 4 moles of ions were produced. Find the number of moles of HA that dissociated. [1] (ii) When 4 moles of H2B was dissolved, 6 moles of ions were produced. Find the number of moles of H2B that dissociated. [1] (iii) Hence, state which acid is a stronger acid. [1] (c) When dry hydrogen chloride gas was passed through a solid zinc strip in an experiment, there was no visible change. A student thus made the following conclusion, “The solid is not zinc as all metals will react with acid.” Pick out and explain two errors present in the student’s conclusion. [2] [Total marks: 6]

2012 End- of-Year Examination Secondary Three 7 Nanyang Girls’ High School Setters: ZJ/CW/ET Chemistry / II [Turn over A5 (a) Crude oil is a liquid mixture made up of different organic substances which needs to be separated. Fig. 1 shows the fractional distillation of crude oil into fractions A to D. Fig. 1 (i) Arrange the different fractions in the order of decreasing boiling point. [1] (ii) Describe the differences in movement and arrangement of particles present at points P and Q in Fig.1. [2] [Total marks: 3] P Q Crude oil A B C D Heat

2012 End-of-Year Examination