KEY. Chemistry Baseline Cornerstone Assessment: Part A. Experimental Design. Directions: Read the paragraph below and then respond to the questions.

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1 Chemistry Baseline Cornerstone Assessment: Part A. Experimental Design Directions: Read the paragraph below and then respond to the questions. Hydrogen peroxide is a liquid that breaks down and releases bubbles of oxygen gas. By adding a catalyst, this chemical reaction occurs faster and is completed more quickly. Patty uses a hydrogen peroxide product with a catalyst to clean her contact lenses every night, and she has to wait until morning for the bubbles to stop forming so she knows the reaction is finished. Patty wants to design an experiment to determine the effect of varying the amount of a catalyst on how fast this reaction occurs. Patty obtains a 500 ml bottle of hydrogen peroxide and 25 grams of the catalyst. 1. What should be the independent variable in Patty s experiment? Explain your choice. Amount of catalyst. This variable is being manipulated to see what effect a catalyst has on reaction time. 2. What should be the dependent variable in Patty s experiment? Explain your choice. Time it takes for the reaction to be complete. This variable relies on the amount of catalyst, so it is dependent. 3. State an appropriate hypothesis for Patty to test. Explain your hypothesis. The more catalyst is added, the faster the reaction. Since a catalyst causes a reaction to occur faster, adding more catalyst should cause the reaction to occur even faster. 4. What condition(s) should remain constant in this experiment? Explain your choices. Yes. Amount of hydrogen peroxide and temperature should remain constant because they could affect the reaction time. 5. A well designed experiment must have a control for comparison purposes. Identify an appropriate control for this experiment. Justify your answer. A trial with no catalyst should be performed so that the reaction time can be compared to trials with a catalyst. The experimenter needs to confirm that the catalyst does change the reaction time. 6. Design a procedure for Patty to carry out to determine the effect of varying the amount of catalyst on the rate of the reaction. List the steps below and the materials needed. 1) Weigh out different amounts of the catalyst. 2) Measure the hydrogen peroxide using a graduated cylinder and pour equal volumes of hydrogen peroxide into 5 test tubes. 3) Do not add any catalyst to the first test tube. Chemistry Baseline Cornerstone Assessment Key Version 1 1

2 4) Add different amounts of catalyst to the remaining 4 test tubes. 5) Using a stop watch, time the reactions and write down the time it takes for the reaction to stop. 7. Create a data table that can hold all the data you would gather through your procedure. Amount of Catalyst 0 g 1 g 2 g 3 g Time Chemistry Baseline Cornerstone Assessment Key Version 1 2

3 Chemistry Baseline Cornerstone Assessment: Part B. Data Interpretation and Analysis and Scientific Reasoning Directions: Read the paragraph below and review the data table. Then, answer the questions that follow. Patty carries out an experiment by measuring out 25 ml of hydrogen peroxide into each of five test tubes. She leaves the first one without any catalyst in order to create a control condition. Then she adds an increasing amount of catalyst (0.5 g, 1.0g, 1.5g, and 2.0g) to four of the test tubes. She starts the stopwatch when the catalyst has been added and lets the reactions proceed until they stop bubbling. When each reaction stops bubbling, Patty notes the time on the stopwatch and records it in her data table. She then repeats the all five reactions two more times. Time Amount of Trial 1 Trial 2 Trial 3 Average Time Catalyst 0g 10 hours 11 hours 10 hours 10.3 hrs 0.5g 6 hours 7 hours 5.7 hours 6.2 hrs 1.0g 2 hours 3.5 hours 1.9 hours 2.5 hrs 1.5g 45 minutes 48 minutes 53 minutes 48.7 min hrs 2.0g 44 minutes 48 minutes 54 minutes 48.7 min hrs 1. Calculate the average time for each amount of catalyst. Show your calculations in the space provided below and follow significant digit rules. Then, write the answer in the blank column of the data table. 0g: ( ) / 3 = g: ( ) / 3 = g: (6 + 7 = 5.7) / 3 = g: ( ) / 3 = g: ( ) / 3 = To graph the data, the time must be in the same units. Convert average time in the final two reactions to hours. Show your calculations in the space provided below and follow significant digit rules. Then, write your answers in the data table min 1 hr X 60 min X = hr Chemistry Baseline Cornerstone Assessment Key Version 1 3

4 3. Create a graph showing the relationship between the amount of catalyst and the average time the reaction took. Graph the data on the grid below. Be sure to label and correctly scale the axes and give the graph a title. Effect of Amount of Catalyst on Reaction Time Tim e of Rea ctio n (hr) Acceptable graph smooth curve, straight lines, or bar graph Examine the data. How does the amount of catalyst affect the reaction time? As the amount of catalyst was increased, it took less time for the reaction to be finished. However, 1.5g seemed to be the maximum amount of catalyst any more than that will not make the reaction go faster. 5. What do you think the time of reaction will be when 2.5 grams of catalyst is used? Explain your answer using the data. I think the reaction will continue to take about 48.7 minutes because using more than 1.5g does not make the reaction go faster. 6. Patty hypothesized that increased catalyst would decrease the time taken for the reaction. Based on this experiment, do you accept or reject her hypothesis? Explain your decision. Chemistry Baseline Cornerstone Assessment Key Version 1 4

5 I would accept the hypothesis. Adding more catalyst did make the reaction go faster. There does seem to be an amount of catalyst that above which no longer makes the reaction go any faster. 7. After completing her experiment, Patty tested the balance she used to measure out the amount of catalyst. She placed a 10-gram weight on the balance, and the balance read out 11 grams. Based on this new information, how would the data Patty gathered change? Would you change your interpretation of the data (question #4)? Explain why or why not. The measured values of the masses would all be incorrect. However, the trend of increasing the amount of catalyst decreases reaction time would not change and I would still accept the hypothesis. Chemistry Baseline Cornerstone Assessment Key Version 1 5