Chemistry. Statistics. General comments. Paper One. Part A Knowledge and simple application Senior External Examination assessment report

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1 Chemistry 2011 Senior External Examination assessment report Statistics Year Number of candidates Level of achievement VHA HA SA LA VLA General comments Paper One: Part A assessed Knowledge and simple application and Part B assessed Scientific processes. Part A consisted of 10 multiple-choice questions and eight short-response questions covering all eight syllabus topics. Marks allocated were in proportion to syllabus topic weightings. Part B contained five Scientific processes questions assessed by criteria specific to each question. In Part B, candidates were required to respond to any four of the five questions. Paper Two assessed Complex reasoning processes and contained five questions assessed by specific criteria. Candidates were required to respond to any four of the five questions. Paper One Part A Knowledge and simple application Multiple-choice questions Question Correct response D A A B B A B D C B % of candidates with correct response

2 Short-response questions This part of the examination required candidates to demonstrate their knowledge and ability regarding simple application of the eight syllabus topics. Many responses indicated that candidates had attempted to learn information without a full understanding of the underlying chemical principles and processes. Consequently, some simple application tasks were often poorly attempted. Question 11 The terms mass number and atomic number were often confused. Some candidates attempted to explain mass number as a mass rather than as a number. a. The majority of candidates were unable to clearly articulate the structural differences between the two allotropes. b. Most candidates failed to clearly state the differences in intermolecular forces arising from the differences in molecular structures. c. Most candidates correctly stated the formula. d. Most candidates correctly stated the name but sulphite was commonly used instead of sulphate. e. Most candidates successfully drew Lewis diagrams. Question 12 a. Most candidates attempted an explanation but clarity varied widely. b. Most candidates successfully balanced the equation. c. i. Most candidates successfully calculated the mass of sulphur dioxide. ii. Some candidates were confused regarding the relationship between molarity, moles and volume of solution. d. Most candidates understood the significance of the coefficients in a balanced equation. e. Most candidates successfully completed the stoichiometric calculation. Question 13 a. The concept of a reducing agent proved a challenge for many candidates. b. Most candidates determined the oxidation number. c. Many candidates failed to recognise the provision of an electrolytic cell and many were unable to correctly represent the required voltaic cell. Labelling of the voltaic cell was not done well. Question 14 a. Very few candidates could represent the required triple ester. b. Most candidates could explain structural isomers but many could not distinguish between straight and branched chains. c. Many candidates failed to recognise the existence of the aldehyde functional group. d. Many candidates represented propyl ethanoate or were unable at all to represent the structure of an ester. 2 Chemistry 2011 Senior External Examination assessment report

3 e. The concept of an addition reaction was not understood by many candidates. f. The majority of candidates could distinguish between an organic acid and a primary alcohol. Question 15 a. Many candidates identified the trend in ionisation energy but most lacked clarity in their explanation. b. Most candidates wrote correct electron configurations. c. Most candidates identified the correct electron configuration and also explained why. Question 16 a. The kinetic theory of gases was well understood. b. The concept of partial pressures was well understood. c. Most candidates successfully used the ideal gas equation. Question 17 a. Most candidates could define entropy and catalyst. b. The concept of energy supplied to break bonds and energy released when bonds form was not well understood. c. Most candidates were familiar with factors which affect rates of reaction. d. Many candidates understood the concept of collision theory involving a series of two particle collisions. Question 18 a. Characteristics of equilibrium systems were not well understood. b. Most candidates could define strong acid. c. Many candidates were unable to successfully write an equilibrium law expression. d. Le Chatelier s principle was well understood. e. Most candidates could identify conjugate acid base pairs. f. Considering the few candidates who successfully responded to Question 18c, responses to this question were surprisingly good. g. Very few candidates successfully calculated the Ka value of a weak acid. Part B Scientific processes Candidates were instructed to respond to only four of the five questions provided. Twelve candidates responded to all five questions. The majority of candidates demonstrated an ability to successfully engage in simple scientific process tasks by processing information, making simple judgments and communicating information in various forms. Queensland Studies Authority February

4 Question 1 The majority of candidates successfully attempted this question. Candidates were able to interpret the given data to construct an activity series. Most candidates also successfully used the table of half-cell reduction potentials to locate the correct position of nickel in the previous activity series. Question 2 The majority of candidates successfully attempted this question. Graphing skills were well developed with labelled axes, suitable selection of scales, correct plotting of points and curves of best fit. Most candidates realised that only the concentration of the potassium iodate was changing. Question 3 Nearly all candidates attempted this question with widely varying degrees of success. Responses indicated that many candidates did not fully understand the chemical principles which underpin the proportions of the two coloured species which together show the colour of the indicator at various ph values. Question 4 Few candidates were familiar with the apparatus used to illustrate the relationship between the pressure of an enclosed volume of gas and its volume. Very few candidates appreciated that the normal atmospheric pressure existed in addition to the bricks. Question 5 Most candidates attempted this question. While many candidates successfully linked substance with bond type, a smaller proportion provided suitable justification for their decisions. Paper Two Complex reasoning processes Question 1 The majority of candidates attempted this question and demonstrated logical reasoning and critical thinking. Very few candidates arrived at a valid response by successfully demonstrating the relationship between boiling point and vapour pressure. Many candidates viewed the task completely in terms of an energy conservation problem. Credit was given for the demonstration of logical reasoning and critical thinking and not for the simple recall of knowledge. Question 2 A small number of candidates attempted this question, with limited success. Several candidates recognised the existence of a common ion effect on the equilibrium. Other candidates calculated a minimum volume of water rather than NaCl(aq). Other candidates anticipated a chemical reaction between AgCl(s) and NaCl(aq) rather than a phase change. Question 3 The majority of candidates attempted this item, with varying success. Many candidates failed to recognise the existence of an electrochemical process and did not use the table of half-cell 4 Chemistry 2011 Senior External Examination assessment report

5 reduction potentials supplied to obtain the required half equations. Many candidates ignored the aluminium completely and attempted a reaction between the silver sulphide and the baking soda. Question 4 Most candidates attempted this item and a considerable number made significant progress. Some candidates confused moles with molarity. Common errors included not checking for reasonableness of responses some candidates obtained volumes of acid in excess of pool volumes. Mathematical errors were common. Question 5 Nearly all candidates attempted this item with widely varying success. Many candidates responded at length but failed to provide an appreciation of the forces associated with the structures and processes. Many did not mention ions, bonds or electrons in their explanations but simply listed known facts, e.g. metals are malleable. In contrast, a number of candidates provided carefully crafted responses which clearly showed the application of critical thinking. Credit was given for the demonstration of logical reasoning and critical thinking and not for the simple recall of knowledge. Sample solutions The sample solutions on the following pages show possible ways of successfully responding to the questions. They do not provide the only valid responses. Other approaches and problem-solving strategies may be equally valid. In Complex Reasoning Processes questions, a valid response must include a demonstration of logical reasoning and critical thinking with reference to the chemistry applicable to the task. Queensland Studies Authority February

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