1. Module C1 Upgrade: Model answers 5 © Oxford University Press 2011 Car exhaust gases Higher tier question Click anywhere on this screen to proceed. Navigate using the links at the bottom of every screen.

2. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer Question (part 1) A mixture of gases come from a car exhaust. (a) The boxes show the names and formulae of some of the gases and diagrams for their molecules. Draw straight lines to connect each gas with the correct diagram. [2] carbon monoxide (CO) nitrogen monoxide (NO) nitrogen (N 2 ) carbon dioxide (CO 2 )

3. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer Question (part 2) (b)Mike works at a garage. He tests the mixture of gases coming from a car exhaust to find the percentage of carbon monoxide. For the car to pass the test the average result must not be greater than 0.4% carbon monoxide. This is the safe limit. He does the test five times. These are his results. Test12345 Percentage of carbon monoxide in exhaust gases 0.4 0.90.30.5

4. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer Question (part 3) (i) Mike works out a best estimate for the percentage of carbon monoxide. His best estimate is 0.4 %. Explain how he worked this out. [2] (ii)Mike thinks that he needs to repeat the test before he is sure whether the car has passed. Explain why he thinks he needs to do this. [2]

5. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer Explanation of question In matching questions like (a), the first name is not always the easiest to work out. Go down each name until you find an ‘easy’ one to start with. One of the boxes holds the ‘key’ to working out the others in this question, notice also that there are more diagrams than names. This is typical of Higher tier choice questions. Look at the number of marks in (b) (i). There are two marks so you need to think carefully about what to do. In (ii), make sure you go back and have a look at the information in the question before trying to answer.

6. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer D–C answer (a) comment This answer for (a) gets no marks. Drawing more than one line to a box means that a correct answer is ‘cancelled out’ by an incorrect answer. It always best to go down all the boxes and make the ‘easy’ choice first. The candidate has correctly worked out nitrogen. This is the key to the others because now it is easier to work out nitrogen monoxide. NextPrevious. carbon monoxide (CO) nitrogen monoxide (NO) nitrogen (N 2 ) carbon dioxide (CO 2 )

7. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer D–C answer (continued) (b)(i)He took an average. (ii)0.4% is the exact limit for the test. comment This response to (b) (i) only gets one mark. By looking at the data more carefully, the candidate would have realised that there is an outlier to consider. Again, this response to (ii) gets one only mark. Two points are needed to gain two marks. The candidate should have realised that all but one of the answers is on or above the safe limit. NextPrevious.

8. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer B–A* answer (a) comment This response gets one mark out of two as one mistake has been made. Starting with nitrogen, the candidate has correctly identified the nitrogen oxide molecule. However, the wrong formula for carbon dioxide has been chosen. It is always wise to look at all of the boxes very carefully when there is an ‘extra’ choice. The extra choice will often be close to the right answer to challenge you. NextPrevious. carbon monoxide (CO) nitrogen monoxide (NO) nitrogen (N 2 ) carbon dioxide (CO 2 )

9. © Oxford University Press 2011 Module C1 Upgrade: Model answers 5 Question Explanation of question Answer B–A* answer (continued) (b)(i)He ignored the outlier and then worked out the mean of the other results. (ii)Most of the results are at the safe limit or higher than the safe limit, and the average is only just on the safe limit. comment This is the correct answer to (b) (ii). However, it would be better to identify the outlier as Test 3 (0.9). This is a good answer for (ii) worth full marks. The candidate has looked back at the information provided in the question and compared it to the results. NextPrevious.