Ausmat Answers Chemistry 2010 free essay sample

Standards describe the kinds of qualities seen across candidate responses in external examination conditions. In late 2010, WACE (written) examination scripts for Chemistry Stage 3 were analysed by teacher expert panels who identified the qualities of candidates’ scripts at each of five performance bands: ‘excellent achievement’, ‘high achievement’, ‘satisfactory achievement’, ‘limited achievement’ and ‘inadequate achievement’. WACE Course scores were reported against these performance bands. The band descriptions for Chemistry Stage 3 are provided in Appendix 1. What do standards tell us? The standards described through the band descriptions tell us, in general terms, how students need to be performing if they wish to achieve a particular ‘standard’. To get a clearer picture of what the standard means, teachers and students can refer to the candidate responses provided. This will help students see what they need to do to improve and help them understand how their work compares with the standard. Standards can also assist teachers in providing students with feedback about their work and see how they might need to modify their teaching. What is provided in this Standards Guide? There are five main components in this standards guide: 1 questions from the examination paper 2 the marking key for each question 3 candidate responses and annotated marker notes 4 statistics such as the highest and lowest marks achieved, mean, standard deviation, etc 5 examiner comments. What standards have been exemplified in this guide? Sample candidate responses which illustrate ‘excellent’ and ‘satisfactory’ performance have been included in this guide, along with marker annotations. In most cases, ‘excellent’ responses received full marks or close to full marks. If there were no responses judged to be ‘excellent’, a ‘high achievement’ response sample may be provided. For questions worth 1 mark (or a small number of marks) judgments about an ‘excellent’ or ‘satisfactory’ standard are less precise. Judgements about ‘excellent’ and ‘satisfactory’ standards illustrated in a candidate response must also take into account the difficulty of the question. It should also be remembered that overall judgments about standards are best made with reference to a range of performances across a range of assessment types and conditions. How well did this examination ‘target’ the ability of candidates? Rasch analysis of raw marks achieved by candidates enables us to provide estimates of question difficulty and student ability, on the same scale. From this relationship, we are able to evaluate how well the questions in this examination were broadly targeted to candidates’ abilities. Data which estimates the difficulty of each question is provided in Appendix 2. A graph showing the relationship between student ability (on this examination) and question difficulty is also provided in Appendix 2. Other points to consider when viewing this guide Use of half marks Examination items are marked out of whole numbers. Half marks occurring in this guide are a result of averaging the whole number marks from each of two markers. Section statistics and marks weightings Section statistics for the highest mark achieved, lowest mark achieved, mean and standard deviation are based on weighted section total marks. Raw mark totals are provided for each section. The raw marks distribution and the weighted total marks distribution is provided on the following page. Examination standards for 2010 WACE examinations The analysis of written examination scripts was used to determine performance band descriptions for 2010. Chemistry: Stage 3 Standards Guide Marks distribution for this examination Number of questions available 25 Number of questions to be answered 25 Suggested working time (minutes) 50 Section Section One: Multiple-choice Section Two: Short answer Section Three: Extended answer Marks available Percentage of exam 25 25 11 11 60 70 35 6 6 70 80 40 Total 100 Chemistry: Stage 3 Standards Guide 5 6 Chemi stry: Stage 3 Standards Guide Section One: Multiple-choice Chemistry Stage 3 Section One: Multiple-choice 25 marks Note: Raw section total marks = 25 Weighted section total marks = 25 Candidates must be encouraged to describe their observations in as much detail as possible. A detailed observation is evidence of a candidate’s full understanding of a process, and more general descriptions of observations cannot be rewarded. The majority of candidates gave the correct structural formulae and organic product names for these questions, although ‘butone’ featured commonly in place of butanone. Some focus should perhaps be given to correct naming of ketones. 40 Chemistry: Stage 3 Standards Guide Section Two: Short answer Question 30(b) Butanoic acid reacts with methanol in the presence of H2SO4. 3 marks) Observations Structural formula of organic product Show all atoms Name of organic product Marking key A fruity smell develops Specific fruit (any fruit) Sweet smell [Single layer forms] Condensed structure also acceptable Structural formula of organic product (show all atoms) H H C H H C H H C H C O O H C H H Question statistics Statistics ID =37 Num ber of attempts = 4126 Highest mark achieved = 3. 00 Lowest mark achieved = 0. 00 Mean = 2. 25 Standard deviation = 0. 95 Question difficulty = Moderate Correlation between question part and section = 0. 62 Observations O CH3 CH2 CH2 C O CH3 Name of organic product Methylbutanoate (methyl butanoate) Description 1 mark for each correct answer for a possible total of 3 marks. Question incorrectly answered or not attempted. Total Marks 1-3 0 3 Chemistry: Stage 3 Standards Guide 41 Section Two: Short answer Candidate responses 30(b) Butanoic acid reacts with methanol in the presence of H2SO4. Notes (3 marks) Observations Structural formula of organic product Show all atoms Name of organic product Excellent response 3/3 marks Correctly completes the table for the esterification reaction. Examiners’ comments This question was not particularly well done. Candidates must be encouraged to describe their observations in as much detail as possible – e. g. a fruity/sweet smell should be described as just that, rather than simply a ‘strong smell’. A detailed observation is evidence of a candidate’s full understanding of a process, and more general descriptions of observations cannot be rewarded. The majority of candidates gave the correct structural formulae and organic product names for these questions. 42 Chemistry: Stage 3 Standards Guide Section Two: Short answer Question Question 31 (3 marks) Condensation polymers form from two monomers, each with functional groups at their terminal carbon atoms (that is, the monomers are difunctional). Examine the polyester structure below. n Question statistics Statistics ID = 111 Number of attempts = 4403 Highest mark achieved = 3. 00 Lowest mark achieved = 0. 00 Mean = 1. 67 Standard deviation = 1. 13 Correlation between question and section = 0. 65 31(a) Circle all the ester linkages (functional groups that link the monomers) represented in the above structure. (1 mark) Marking key Question statistics Statistics ID = 38 Number of attempts = 4313 Highest mark achieved = 1. 0 Lowest mark achieved = 0. 00 Mean = 0. 60 Standard deviation = 0. 49 Question difficulty = Moderate Correlation between question part and section = 0. 27 n Description All ester linkages identified and circled (end linkages may also be circled). Question incorrectly answered or not attempted or not all linkages circled. Total Marks 1 0 1 Chemistry: Stage 3 Standar ds Guide 43 Section Two: Short answer Candidate responses 31(a) Notes Circle all the ester linkages (functional groups that link the monomers) represented in the above structure. (1 mark) No candidate response is provided. Refer to marking key. Excellent response Examiners’ comments A significant number of candidates did not correctly identify the ester linkages in the polymer in this question. 44 Chemistry: Stage 3 Standards Guide Section Two: Short answer Question 31(b) Identify the two monomer compounds (A and B) used in the production of this polymer and draw their molecular structures. (2 marks) Marking key Monomer A Question statistics Statistics ID = 39 Number of attempts = 4250 Highest mark achieved = 2. 00 Lowest mark achieved = 0. 00 Mean = 1. 12 Standard deviation = 0. 93 Question difficulty = Moderate Correlation between question part and section = 0. 64 OH C O Monomer B O C OH H H O C H H C H Marks 2 1 0 2 O H Description Both monomers correctly identified and drawn. One correct monomer or both monomers slightly incorrectly drawn. Question incorrectly answered or not attempted. Total Chemistry: Stage 3 Standards Guide 45 Section Two: Short answer Candidate responses 31(b) Notes Identify the two monomer compounds (A and B) used in the production of this polymer and draw their molecular structures. (2 marks) Excellent response 2/2 marks Correctly identifies the two monomers needed to form the polymer. No candidate response is provided. Refer to marking key. Satisfactory response Examiners’ comments The two component monomers were reasonably well identified. 46 Chemistry: Stage 3 Standards Guide Section Two: Short answer Question Question 32 (12 marks) For each species listed in the table below, draw the structural formula, representing all valence shell electron pairs either as : or as — and state or draw the shape of the molecule and state the polarity of the molecule. (for example, water H O H or H O H or H O H bent polar) Polarity of molecule (polar or non-polar) Species Structure (showing all valence shell electrons) Shape (sketch or name) nitrogen trichloride NC? 3 methanal HCHO sulfur dioxide SO2 carbon dioxide CO2 Chemistry: Stage 3 Standards Guide 47 Section Two: Short answer Marking key structure (showing all valence shell electrons) Shape (sketch or name) Polarity of molecule (polar or nonpolar) Question statistics Statistics ID = 40 Number of attempts = 4498 Highest mark achieved = 12. 00 Lowest mark achieved = 0. 00 Mean = 9. 83 Standard deviation = 2. 17 Question difficulty = Easy Correlation between question part and section = 0. 67 Species nitrogen trichloride NC? 3 Cl N Cl Cl pyramidal polar O methanal HCHO H C H trigonal planar polar O sulfur dioxide SO2 or O S bent polar O O S O carbon dioxide CO2 O C O linear non-polar Description 1 mark for each correct answer for a possible total of 12 marks. Question incorrectly answered or not attempted. Total -1 if non-bonding electrons missing overall Marks 1-12 0 12 48 Chemistry: Stage 3 Standards Guide Section Two: Short answer Candidate responses Question 32 Notes (12 marks) For each species listed in the table below, draw the structural formula, representing all valence shell electron pairs either as : or as — and state or draw the shape of the molecule and state the polarity of the molecule. (for example, water Species H O H or H O H or H O H bent polar) Polarity of molecule (polar or non-polar) Structure (showing all valence shell electrons) Shape (sketch or name) nitrogen trichloride NC? 3 methanal HCHO sulfur dioxide SO2 carbon dioxide CO2 Chemistry: Stage 3 Standards Guide 49 Section Two: Short answer Candidate responses Notes Excellent response 12/12 marks Correctly draws structures and identifies shapes and polarity of each species. 50 Chemistry: Stage 3 Standards Guide Section Two: Short answer Candidate responses Notes Satisfactory response 8/12 marks Draws and identifies shape and polarity of three species. However, presents incorrect information for methanal. Chemistry: Stage 3 Standards Guide 51