Exemplar for Internal Assessment Resource Chemistry Level 1. Resource title: Investigating Reaction Rates

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1 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Exemplar for Internal Assessment Resource Chemistry Level 1 Resource title: Investigating Reaction Rates This exemplar supports assessment against: Achievement Standard Carry Out a Practical Chemistry Investigation, With Direction Expected responses The moderators have developed expected student response from a wide variety of sources. Date version published by Ministry of Education December 2010 To support internal assessment from 2011 Crown 2010

2 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: Low Excellence To achieve with Excellence, a full explanation of the chemistry idea is required. That is; Increasing temperature increases the kinetic energy of the reactant particles. The collisions of reactant particles will therefore have more energy. Therefore an increased proportion of the collisions these will now be successful so the successful collision rate of particles is increased. Without a reference to the energy of particles, and as a consequence, the increase in successful collision rate of particles, the explanation is not complete. In addition, as there was difficulty in repeating the reaction under the same conditions, the discussion needs to include comment related to the difficulty of obtaining and maintaining the same temperature. 1. No unit for measurement of time. 2. Successful collisions of what? Reference to particles is required. Also, no reason for this. 3. Conclusion is completed, linking to purpose. 4. Incorrect statement regarding other variables. 5. Irrelevant as a drop or two of water is insignificant in the total volume of 60 ml. 6. Same person should determine time taken. Crown 2010

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5 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: High Merit The method, while not well written, describes what has been done including temperatures to be used. Results are recorded in an appropriate way although no units have been given for times taken at room temperature. Repeats have been carried out. Evidence of processing as averaging of time taken has been correctly done and graph has been drawn. Repeats have been carried out for the 4 values of independent variable used and other significant variables have been controlled. Conclusion is based on processed data and links to the purpose. However, the conclusion is not written as a simple statement, as would be expected but appears at the end of the first paragraph and is then repeated. The chemistry idea has not been correctly explained. High temperatures mean that the particles have as much kinetic energy. There is no justification for more successful collisions per second. Similarly, explanation for decreased rate at low temperatures is lacking. Incorrect statement referring to other variables since there is only one dependent variable, time, and others must be controlled. Intended temperatures to use were 20, 40, 60, and 80 degrees. However, temperatures recorded differ a little. While this is not a major issue from a practical point of view, this needs to be referred to in the discussion as averaging different temperatures is not valid and will not increase accuracy of results since the relationship between temperature and time is not a linear one. While repetition does show reliability, the temperatures used would need to be extremely similar. There is no part of the discussion that considers the issue of temperature. The factors discussed and related to accuracy are trivial. As the observation of no longer being transparent is made looking down through the reaction mixture, the depth of solution is the critical factor and this is why the same container must be used, along with the same volumes of solution. As the flask will always be wet due to repeated use, this is a variable that requires controlling further. It is noted that two observers were used for determining time taken. This is a variable that could have been controlled. Crown 2010

6 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: Low Merit The method describes what has been done although temperatures to be used need to be included. Also, it is not clear that a measuring cylinder was used to measure volume of thiosulfate solution. Sizes of measuring cylinders used have not been stated in either the list of equipment or the method. More detail in the method used is required to provide evidence for accuracy and reliability of data produced. Results are recorded in an appropriate way although the unit for time for the first temperature is incorrect since this would have been minutes:seconds. The graph has not been drawn carefully as the scale used for temperature has not been used accurately. However, processing is sufficient. Repeats have been carried out for the 5 values of independent variable used and other significant variables have been controlled. Conclusion is based on processed data and links to the purpose. Justifying choices made for accuracy is very limited. If the same measuring cylinder is used for the same solution it does not need to be washed and dried. Also, using the same sized glassware will mean any solution left in the measuring cylinder could be assumed to be constant. Relating findings to the chemistry idea is incomplete as it is not based on rate of successful collisions of particles. 7. A measuring cylinder needs to be used to measure the volume of sodium thiosulfate solution. 8. Temperatures to be used need to be stated. 9. Incorrect unit for time. 10. Conclusion relates to purpose. 11. As a consequence, a greater proportion of collisions, in a given time interval, will be successful. Crown 2010

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10 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: High Achieved The student has underlined the purpose given and has designed a procedure to investigate this. The procedure has been carried out, data recorded and processed appropriately. However, while an appropriate interpretation of the processed data has been made, the conclusion does not link to the purpose. The purpose was to investigate how the rate of reaction changes and the student has written the conclusion from the perspective of time taken for reaction. The procedure used also lacks detail. It does not describe how the volumes of solutions were measured, although the equipment list included a 100 ml measuring cylinder. Heating the thiosulfate solution in a beaker and then pouring into a conical flask is not a technique that will increase the accuracy of measured value of the independent variable (temperature). This is demonstrated in the range of temperatures actually used for each value of the independent variable. Repeats for each value of the independent variable have been carried out and processing of data has been done with determining average time and drawing a graph. As a stop watch measures minutes: second, the 3 rd reading at room temperature has been incorrectly recorded. An interpretation correctly based on processed data has been written. However, the conclusion made does not link to the purpose. The conclusion would need to be related to the purpose, how temperature affects the rate of reaction, for a judgement of Merit. 12. No detail related to how the volumes of solutions were measured. 13. Changing thiosulfate solution from beaker to flask may introduce inaccuracy with temperature. 14. An incorrect recording of time? 15. Conclusion links temperature and time for the reactant to react. Crown 2010

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14 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: Low Achieved The student has carried out the investigation, obtained data and made a conclusion. While the procedure used could probably be followed by another person, it lacks detail. It does not describe how the volumes of solutions were measured, although the equipment list included both 20 ml and 100 ml measuring cylinders. There is no detail related to how the sodium thiosulfate was heated although the equipment list included a thermometer and a heating plate. A diagram has been drawn but is not labelled. The first 4 steps of the procedure suggest the reaction will be carried out 3 times for each temperature stated although the results show only two sets of data. While in the table of data values of dependent and independent variables lack the appropriate units, a key is provided for time and correct units for both time and temperature are shown on the graph. Correct processing is shown in averaging results and drawing the graph. An interpretation and conclusion, correctly based on processed data, have been written. The conclusion links to the purpose. 16. As the reaction involves only solutions, surface area is not a relevant variable to be controlled. This comment can be ignored. 17. No detail related to how the volumes of solutions were measured. 18. No detail related to how the solution was heated. 19. No unit recorded for temperature. 20. No unit recorded for time in table. However, a key shows how to read the time data. 21. Data is presented appropriately and time has been averaged correctly. 22. Graph is drawn appropriately with correctly labelled axes. 23. Interpretation of data and conclusion written. Crown 2010

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20 Exemplar for internal assessment resource Chemistry 1.1A for Achievement Standard Grade Boundary: High Not Achieved While the procedure used could probably be followed by another person, it lacks detail as it does not describe how the volumes of solutions were measured, or how the reaction mix was heated. Equipment listed on planning page is only described as lab equipment rather than the specific equipment to be used. The first four steps of the method indicate the reaction is carried out three times at room temperature and step 5 implies that the reaction will be carried out 3 times at each of the values given for the temperature. As the result table only shows two different times for each temperature, the range of values have been repeated but twice, rather than three times. This is not a major problem although the method described should be the final method used. Units for reaction time recorded in the result table are not seconds for the first two columns, as suggested, but minutes and seconds. Apart from a minor error in processing for the first temperature (average is 128 s), processing of data to determine average time is appropriate. The time taken for the first temperature used has not been recorded on the graph but remaining points are correct and provide sufficient data. While there are no labels or units on the axes of the graph, units have been recorded in the result table. Processing of data to determine average time was appropriate. The major issue is that the student did not write an interpretation or conclusion. A simple statement interpreting the results would have lead to a judgement of Achieved samples indicates 3 trials will be carried out for each temperature. 25. No use of measuring cylinders to ensure volumes measured accurately. 26. No description of how different temperatures achieved. Were both solutions heated to the temperatures stated? 27. Time recorded should be minutes:seconds, not seconds. 28. Label of temperature is required for x-axis, as well as unit for measurements. 29. Label of time is required for y-axis, as well as unit for measurements. 30. Graph should have a title. 31. No interpretation of data, or conclusion, written. Crown 2010

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