NYGH 2014-S3MYE-Chem P2

Class Register Number Name NANYANG GIRLS’ HIGH SCHOOL Mid Year Examination 2014 Secondary Three CHEMISTRY 1 hour 30 minutes Section B and C Theory Paper Tuesday 6 May 2014 1145-1315 Additional materials: Writing paper 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 B (30 marks) Answer all questions. Write your answers in the spaces provided on the question paper. Section C (10 marks) Answer all questions. Write your answers on the separate writing paper provided. At the end of the examination, Hand in the writing paper separately. INFORMATION FOR CANDIDATES Examiner’s Use Section A Section B Section C Total The intended number of marks is given in the brackets [ ] at the end of each question or part question. Setters: LXT/ZJY This document consists of 9 printed pages. NANYANG GIRLS’ HIGH SCHOOL [Turn over

2014 Mid Year Examination Secondary Three 2 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry Section B Answer all questions. Write your answers in the spaces provided. B1 A few drops of concentrated nitric acid were added to pieces of copper at the bottom of a tall bell jar. A reddish-brown nitrogen dioxide gas was formed and all the copper reacted in a very short time. The red-brown colour slowly moved up the gas jar but initially the colour remained darkest at the bottom. After thirty minutes, the reddish-brown colour was uniform throughout the gas jar. (a) Bromine is another reddish brown gas. Which gas, bromine or nitrogen dioxide, will fill up the whole jar in a lesser time? Give a reason for your answer. [2] (b) Explain how and why the results would differ if the gas jar was placed in hot water before carrying out the experiment. [2] Total [4] B2 Four elements P, Q, R and T, have proton numbers between 2 and 12. An atom of P has one electron less than a noble gas (Group 0 element). An atom of Q has three electrons less than a noble gas. An atom of R has one electron more than a noble gas. The atom of T has the same total number of electrons as P but the mass number of T is 1 more than that of P. (a) Write the chemical formula of the compound formed between (i) P and Q : __________________ [1] (ii) P and R : __________________ [1]

2014 Mid Year Examination Secondary Three 3 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry [Turn over (b) Draw the Lewis dot diagram of the compound formed in (a)(i) [1] (c) What is the relationship between P and T? [1] Total [4] B3 A mixture of amino acid was separated by paper chromatography using two different solvents. After treating with a locating agent, the results are shown below. The position of the amino acids on the two chromatograms are labelled W, X and Y. (a) From the chromatograms, explain in term of Rf value, whether X is more soluble in solvent A or B? [2] Solvent A Solvent B

2014 Mid Year Examination Secondary Three 4 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry (b) The Rf values of a number of amino acids in the two solvents are listed below. Amino acid Rf value in solvent A Rf value in solvent B Alanine 0.72 0.38 Glutamic acid 0.38 0.30 Tyrosine 0.66 0.45 State the identity of W based on the values above. W : __________________ [1] Total [3] B4 Boron nitride, BN, exists in two physical forms. The structures of these forms are shown below. (a) Suggest why boron nitride with structure A can be used as a lubricant. [2] (b) Suggest a use of boron nitride with structure B. [1] Total [3]

2014 Mid Year Examination Secondary Three 5 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry [Turn over B5 Campden tablets are composed of a mixture of sodium metabisulfate Na2S2O5, and various preservatives. They are used during wine-making to sterilise equipment by dissolving them in water and adding a monobasic organic acid HA. These two components react together to produce sulfur dioxide, a sodium salt of the organic acid, NaA, and water. (a) Write a chemical equation for the reaction of sodium metabisulfate with the acid. [1] (b) HA is a weak organic acid. Explain what is meant by a “weak acid”. [1] (c) Write the chemical equation for the dissociation of the acid. [1] (d) What is the nature of sulfur dioxide? Describe a reaction that can be used to determine the nature of sulfur dioxide. [2] Total [5] B6 Salts can be prepared by various methods depending on the chemical nature of the salt. (a) Alex was given copper(II) sulfate solution and he was asked to prepare pure copper(II) nitrate crystals. State briefly how this could be done. [2]

2014 Mid Year Examination Secondary Three 6 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry (b) A 20 cm3 sample of aqueous barium hydroxide was titrated with 40 cm3 of 0.12 mol/dm3 of dilute sulfuric acid. The conductivity of the solution, which is its ability to conduct electricity, was measured throughout the titration and the results shown in the graph below. Explain the changes in conductivity shown by the graph. [3] (c) Outline the steps you will take to obtain a pure sample of the salt formed from the reaction mixture after 40 cm3 of sulfuric acid is added. [2] Total [7] Volume of H2SO4 added/cm3 0 25 40 Conductivity/ Sm mol-1

2014 Mid Year Examination Secondary Three 7 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry [Turn over B7 A brown compound E is insoluble in water. When dilute hydrochloric acid is added to E, effervescence of a colourless and odourless gas G is observed. The brown compound dissolves in acid to form a yellow solution. (a) State with reasons, a cation and an anion that could not be present in compound E. [2] (b) What is the identity of E ? __________________ [1] (c) Using your answer in (b), write an ionic equation for the reaction of E with hydrochloric acid. [1] Total [4]

2014 Mid Year Examination Secondary Three 8 Nanyang Girls’ High School Setters: LXT/ZJY Chemistry Section C Answer all questions from this section in the writing paper provided. C8 The reaction scheme below shows the relationship between compounds P to U. Solution P and Q react together to produce Solution R and Precipitate S. P, Q, R and S are also subjected to other tests individually to deduce their identities. (a) State the formulas of the cations in P and Q [2] (b) State the formulas of anions in R and S [2] (c) Hence deduce the identities of R and S. [2] (d) Write the ionic equation for the reaction between P and aqueous sodium hydroxide. [1] (e) State the effect of carbon dioxide gas on moist red litmus paper and give a reason for your answer. [2] (f) Describe the observations that will be made when excess aqueous ammonia is added dropwise to Solution R. [1] End of paper Solution P Solution Q + Solution R A gas which turns moist red litmus blue was evolved. Warmed with aqueous sodium hydroxide Add aqueous silver nitrate and excess dilute nitric acid Precipitate S + W