Item Description: This investigation is intended to show the student the relationship between the temperature and reaction rate of a mixture. The student is told that the reaction rate, defined as the amount of time for a given number of atoms and molecules to react, depends on the average speed of the molecules which depends on the temperature. The student adds two reactants to a uniform amount of water at three different temperatures (all hot, 3 parts hot: 1 part cold, and 1 part hot: 1 part cold). The student stirs the mixture and observes its color, recording the amount of time it takes for the reaction to occur (as indicated by color change from purple to yellow). Question 1 asks the student to graph the temperature of the mixture against the time the reaction occurred for each case. A good answer will consist of a properly labeled graph. Each axis should be labeled either "time" or "temperature" and the axes should be marked with a scale approximate for the data obtained. The three graphed points should be connected with a straight line. The line does not have to pass through each point but should come as close to each point as possible. The graph should fill at least 1/2 of the graph paper provided. Temperature should be on the "y" axis and time on the "x" axis. An example follows under Criterion 2. Question 2 asks the student to explain how the relationship between temperature and reaction rate can be applied to everyday life and give an example to support the explanation. A good response should state the relationship between temperature and reaction rate and describe a specific situation where temperature is related to reaction rate in an everyday experience. This explanation should be scientifically correct. In addition, the student's explanation should be supported by a specific example. The Item: Question #1: On the sheet of graph paper below, plot the temperature (degrees Celsius) of the mixture versus the time (seconds, or sec) when the mixture began to turn yellow. Draw a smooth line that passes near (but not necessarily through) all the data points. Question #2: On the basis of your conclusion in Question 2, explain how the relationship between temperature and reaction rate is used in everyday life. Give an example to support your explanation. Comments: In the data table it is more appropriate, given the length of the experiment, to calculate the reaction times in minutes instead of seconds. Therefore, the graph may be labeled in minutes or seconds. Also, due to the length of this experiment, many students did not complete the data collection. Criterion 1 takes this situation into account. Finally, there is a misprint in Question 2. "On the basis of your conclusion to question 2 . . ." This reference to a previous question 2 in the only question 2 on the test is confusing to some students but most figure out that it is a mistake. The student is never asked to formally state the relationship between temperature and reaction rate. This is taken into account in Criterion 3. ME120B Rubric Criterion 1: The student has completed at least part of the data table and at least one of the following: Observations are written out for the experimental cases that were completed. These may include ideas about why the experiment did not work, color changes, calculations or other relevant notes. (Data table) For example: 3rd time - no change. I think we should have tried 150 ml of cold water and 50 ml of hot. Maybe cold changes it. The student notes that they did not draw a previous conclusion about the relationship between temperature and reaction rate. (Question 2) For example: We did not draw a conclusion in Question 2 - this is Question 2. The student notes that they could not draw a conclusion about the relationship between temperature and reaction rate because their experiment did not work. (Question 2) For example: I do not know the relationship because we didn't have time to do both hot and cold. The graph is properly labeled "time" and "temperature" but incomplete because the experiment was not complete or did not work. (Question 1) OR The student's completed graph is partially correct. (Question 1) For example: The axes are labeled correctly but the points do not correspond to the data. The points are correctly placed on the graph but the axes and/or the scale are not labeled properly. The graph is very, very small - crammed into the corner of the graph paper so that it is difficult to read. The "temperature" label is on the x axis and "time" is on the y axis. The points are correctly placed according to the student's data. Criterion 2: The graph is correctly completed and labeled. A line is drawn between the points. The point should correspond to the data table. (Question 1) For example (numbers are estimated): OR If no data has been obtained, the student predicts what they think might have occurred and draws a correct conclusion about what the relationship between temperature and reaction rate might be. (Question 2) For example: If it had turned yellow, the time and temperature would most likely have shown that a higher temperature requires shorter time. The solution did not turn yellow, so we could not state the conclusion, but I think that the hotter the water, the faster the reaction. Criterion 3: The student draws a conclusion about temperature and reaction rate from experimental data. (Question 2) For example: From the graph you can see that if the temperature goes down, the reaction takes longer. Generally, when the temperature is increased, the rate of reaction is increased as well. OR The student lists or describes a situation from everyday life that illustrates the temperature and reaction rate relationship. The reaction referred to should be scientifically correct and chemical in nature. (Question 2) For example: The higher the temperate, the faster the reaction. One place in everyday life where this can be seen is in cooking. To make a type of food melt more quickly, it is often heated. Not acceptable: An example in everyday life is when you run and your body gets hot, your heart beats faster. Criterion 4: The student applies the temperature and reaction rate relationship to an everyday situation and correctly describes what occurs at the molecular level. (Question 2) For example: With reference to an ice cube. If the temperature is raised the molecules begin to move faster, collide more often, and consequently the ice melts. Thus as the temperature rises, so does the rate of reaction. OR The student applies the temperature and reaction rate relationship to an everyday situation and correctly describes in detail the chemistry that occurs in the reaction. (Question 2) For example: Take for example, developing film. When developer is added to film, it produces a chemical reaction that washes off the silver bromide crystals. When the developer is warmer, the reaction occurs more quickly.