Report on the Examination

Transcription

1 Version 1.0 General Certificate of Secondary Education Science A / Chemistry CH1FP (Specification 4405 / 4402) Unit 1: Chemistry 1 Report on the Examination

2 Further copies of this Report on the Examination are available from: aqa.org.uk Copyright 2013 AQA and its licensors. All rights reserved. Copyright AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the school/college. Set and published by the Assessment and Qualifications Alliance. The Assessment and Qualifications Alliance (AQA) is a company limited by guarantee registered in England and Wales (company number ) and a registered charity (registered charity number ). Registered address: AQA, Devas Street, Manchester M15 6EX.

3 General The paper was out of sixty marks and the students had one hour in which to complete it. There were seven questions on this paper. Questions six and seven were common to Foundation and Higher Tiers. They were targeted at grades D and C. The first five questions were targeted at grades G to E. These papers are more difficult for students than previous papers on core chemistry. This reflects the requirements of the new GCSE subject criteria and the new specification. Half of the marks on the paper are for application of skills, knowledge and understanding in practical and other contexts and for analysing and evaluating evidence, making reasoned judgements and drawing conclusions. Students should be prepared to expect that they will be given unfamiliar contexts and information that assess these objectives. Familiar contexts are those mentioned in the specification and assess recall, selection and communication of students knowledge and understanding. The mark scheme was designed to allow students to gain marks for showing knowledge, understanding and application of chemistry. The extended response questions caused problems for some students who could not organise or express clearly their answers. The majority of students appeared to have sufficient time to complete the paper. Too many students used up a lot of space by repeating the question, which really is not needed in an examination as it does not gain them any credit. There were a large number of students whose scripts were difficult to read, either due to poor handwriting or the use of pens other than black, or both. Basic knowledge and understanding of how science works in familiar and in unfamiliar situations, including in the laboratory, are tested throughout this paper. Students must read and analyse the information provided, then read and understand the question before writing their response. Students should then read through their answers, especially those that are descriptions or explanations. Many students use it or they without any clear indication of what the student is referring to. Question 1 (Low Demand) (i) The majority of students achieved the mark for knowing that at the centre of an atom is the nucleus. (ii) Many students achieved the mark for knowing that around the centre of an atom are energy levels (shells). (b) (c) Most students scored full marks for understanding numbers of protons and electrons in atoms and for knowing the term mass number. The most common problem was that students scribbled out link lines and drew new link lines but did not always make it clear which lines were their final choice. Students must read and analyse the information provided, then plan their answer before drawing the link lines. A few students had drawn only one link line because they had not understood the instruction to draw one line from each question to its correct answer. Note that no credit can be given when two or more lines are drawn from a question to two or more answers. The majority of students worked out that the percentage of the rest of the elements in the Sun was 2%. The most common incorrect responses were either 98% or 12%. 3

4 (d) (i) Students were advised to use the Chemistry Data Sheet to help them answer this question. From the periodic table most students did realise that a neon atom has 10 protons, however, 20 protons was a common incorrect answer. (d) (ii) Students were advised to use the Chemistry Data Sheet to help them answer this question. From the periodic table most students did realise that helium and neon are in group 0. Noble gases was an acceptable answer. Common answers not gaining credit included non-metals and gases. Question 2 (Low Demand) Just over half of the students achieved full marks for knowing that the crust has mountain ranges, there are convection currents that cause earthquakes in the mantle and that the atmosphere is a mixture of gases. Students displayed the same problems drawing link lines as they did in Question 1(b). (b) (I) The majority of students achieved the mark for understanding that Iceland has volcanoes because it is on a tectonic plate boundary. (b) (ii) Most students gained the mark for knowing that scientists cannot accurately predict when volcanic eruptions will occur. (c) Surprisingly few students gained full marks for appreciating that solid ash particles cause global dimming and for knowing that sulfur dioxide causes acid rain. Question 3 (Low Demand) (i) Most students were unable to correctly spell emulsion. There were several blanks and many incorrect sentence completions such as, emulsifier, alloy, compound or element. (ii) The question asked for one benefit of using emulsifiers that are in food. Most students did not gain credit because they just repeated that the emulsifier helps olive oil and water mix. Credit was awarded if students stated that the emulsifier prevents the olive oil and water from separating. Most of the credit given was for tastes better or better texture. Common incorrect answers were that emulsifiers are healthy or are not fattening or preserve food or keep food fresh. (b) (i) Several students thought that compared means differed so these students gave 200 o C as an incomplete answer. The answer 200 o C more was acceptable. The sentence completion that water is only 100 o C was allowed credit. (b) (ii) Most students gained at least one mark. The common correct answers were more fat and different flavour. Students often stated better texture without mentioning that the food would be crisper or harder. Answers that mentioned the difference in boiling points usually did not relate this to the effect that the food cooks quicker in olive oil. Many students did not gain credit because they just gave a description of frying and boiling, or thought that foods are healthier if they contain fats. Several students gave different colour, even though the stem of the question stated apart from colour. 4

5 Question 4 (Low Demand) (i) Most students gained at least one mark. The most common correct answers were provides jobs and a specified type of pollution. There were a number of vague answers that did not describe the impacts and just stated pollution or carbon dioxide produced or non-renewable. A number of students also referred to the process of producing iron or steel instead of the quarrying of iron ore. (ii) Few students knew that ores contain enough metal to make extraction of the metal economic. (b) Surprisingly poorly answered because most students thought that by coke or by coke and air were sufficient for the answer. There were a range of interesting responses that did not gain credit such as, the blast furnace is heated by the Sun, a bunsen burner, hot air, a flame, fire and electrolysis. Although many students mentioned coke and air, they did not state they react just that they are added. Several students did not mention coke but suggested other fuels such as coal or natural gas as being used to heat the blast furnace. (c) (i) Many correct answers were given but it is surprising that a significant number of students still could not name iron oxide calling it iron ore and carbon dioxide was often called carbonate, cobalt or carbon monoxide. (c) (ii) Few students understood that iron is extracted from its ore by reduction. (d) (i) Very few students gained any marks. The most common incorrect idea was that oxygen is stronger so it pushes or blows the carbon out. Most students who got one mark did so for knowing that carbon dioxide is produced. Other incorrect suggestions were that oxygen is more reactive than carbon so removes it by decomposition or by neutralisation or by reduction. (d) (ii) Most students knew that metals, such as nickel, are added to low-carbon steels to make the steel much harder. (e) Most students gained at least one mark. The most common correct answer was the advantage that less carbon dioxide is produced. Several students thought that four ticks were needed, that is, one in each row. Many incorrectly thought that the disadvantage was more iron needs to be mined. Question 5 (Low Demand) (b) Most students scored at least one mark. It was disappointing that there were very few students scoring both marks, with many students not attempting an answer. A significant number of students do not have a basic understanding of chemical equations. If students gained a mark it was usually for carbon dioxide. Many students incorrectly thought that the complete combustion of octane produces carbon and hydrogen. Also a common incorrect product was octane oxide. (c) (i) Most students knew that the reaction to produce ethanol from sugar solution is fermentation. 5

6 (c) (ii) Very few students were awarded both marks. There were many poor answers such as carbon dioxide being given off rather than the plants taking it in or the incorrect idea that ethanol does not produce carbon dioxide when burnt. There were mostly vague reasons such as ecofriendly, natural, cheap or no pollution. If students gained a mark it was usually for renewable resource or ethanol produced from plants is carbon neutral. (c) (iii) Again very few students were awarded both marks. There were mostly vague answers. No credit was awarded for students who stated that it was a long process because it takes time for crops to grow or that ethanol would run out if we use or drink too much. Most students were not linking a reason to the bad effect on the environment, for example, land could be used for food crops instead of growing more sugar cane requires a lot of land. Question 6 (Standard Demand) Few students seemed to have experience of this type of practical work. Very few students said that timing must be started at the same time as heating was started. Several students waited for the bubbles, rather than the limewater going cloudy. Many students recognised the limewater was to test for carbon dioxide, although the timing marking point was seen very rarely. The most common attempt at timing simply repeated the information given in the question time how long it took for carbon dioxide to be produced. There were a few students who did not attempt the question and some who simply described the set up shown in the diagram. (b) (i) Most students felt that the limewater had not changed because the release of carbon dioxide was too slow. A very small proportion of students realised that the copper carbonate was not yet decomposing or not yet hot enough, although even fewer recognised that the gas bubbles were due to expanding air. Most students did not know that copper carbonate was green and said that it had reacted (usually with oxygen) and had changed to a green colour. Other students thought that the bubbles were caused by the limewater boiling. Poor examination technique meant that a number of students did not suggest reasons and merely rephrased the observations. (b) (ii) A few students appreciated that the copper carbonate was now decomposing, producing carbon dioxide. A number of explanations referred to the copper carbonate burning or melting or boiling indicating a poor understanding of key chemical or physical changes in chemistry. Other students talked about a reaction between limewater and the copper carbonate. Many students continued to describe what was happening rather than explaining the observations. Several students were able to gain one of the marks for linking the change in the limewater colour to the production of carbon dioxide gas. A number of students did refer to an increase in temperature but did not explain that this then resulted in the thermal decomposition of the copper carbonate. (b) (iii) Hardly any students appreciated that copper oxide was the black solid that remained. The misconceptions were that the copper carbonate had been burned, due to overheating, or that the powder was black due to soot or carbon forming. Poor examination technique led to answers such as it had finished, where it was unclear what they were referring to. 6

7 Question 7 (Standard Demand) The question was poorly answered. The main mark gained was for the fact that the fractions or hydrocarbons have different boiling points. The explanation of the separating into fractions was often confused and many responses lacked the detail to gain any marks. The omission of any reference to vapours was common. Some students confused processes and had a catalyst splitting up crude oil; slag falling to the bottom of the tower and even filtering made an appearance. (b) The question was poorly answered. Knowledge that alkanes are hydrocarbons was the most common mark, although a very small number of students included saturated for the second marking point. Many students did not gain the mark because of contradictions such as saturated compounds have carbon-carbon double bonds. The inclusion of the general formula for alkanes was rare. (c) Students have become more familiar with these longer QWC questions and most students scored marks. Disadvantages were well described, possibly as they fitted in with learning about finite resources and types of pollution. Advantages were harder to define as it required using a combination of information from the graph, information in the text and their own analytical powers. Despite this some good answers were seen. However, there were several students who just simply copied out the question word for word without telling us what was an advantage or a disadvantage. Of the science points, the most common advantage was that this represented a large oil reserve. However no credit was given for figures taken directly from the text without explanation. Increased employment was another advantage, which better students related to the economy of the area and Canada and sometimes to improved facilities and infrastructure for local people. For disadvantages, many students were able to list two or three forms of pollution with the best descriptions linking deforestation to a reduction in biodiversity as well as contributing to global warming by removal of photosynthesising trees. There was great concern for the trees; usually because this would result in a lack of oxygen in the atmosphere. Only the better students mentioned that crude oil is non-renewable or the large amounts of energy, with resulting pollution, are needed to extract and process the oil. There were some common misconceptions, such as natural gas being carbon neutral because it was natural. Grade boundaries and cumulative percentage grades are available on the Results statistics page of the AQA website UMS conversion calculator 7