KEY. Chemistry End of Year Cornerstone Assessment: Part A. Experimental Design

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1 Chemistry End of Year Cornerstone Assessment: Part A. Experimental Design Directions: Read the paragraph below and then respond to the questions. Baking soda and vinegar react to form carbon dioxide gas. Patty's little brother is making a science fair volcano for a project, and he wants to create a big explosion. The volcano is designed to hold 10.0mL of vinegar. Patty offers to help her brother set up an experiment to determine how much baking soda, when reacted with the 10.0mL of vinegar, will release the most carbon dioxide. Patty obtains 100.0mL of vinegar, 25.0g of baking soda, 5 plastic bottles, 5 balloons, a spool of string, and a meter stick. 1. What should be the independent variable in Patty's experiment? Explain your choice. The amount of baking soda. This variable is being manipulated to see its effect on amount of CO 2 produced. 2. What should be the dependent variable in Patty's experiment? Explain your choice. The amount of CO 2 formed. This variable relies on the amount of baking soda, so it is dependent. 3. State an appropriate hypothesis for Patty to test. Explain your hypothesis. The greater the amount of baking soda, the more CO 2 will be produced. 4. Are there conditions that should remain constant in this experiment? Explain your answer, and give examples, if necessary. Temperature, size of container, amount and brand of vinegar, brand of baking soda these could change the amount of CO 2 produced, so they must be kept constant. 5. A well designed experiment must have control for this experiment. Justify your answer. A control in this experiment would be to test if any CO 2 forms if no vinegar is added to the baking soda. 6. Design a procedure for Patty to carry out to determine the effect of varying the amount of baking soda added to the amount of gas produced. List the steps below and the materials needed. 1. Add equal amounts (volumes) of vinegar to the 5 bottles. 2. Weigh out 5 samples of baking soda each a different mass. 3. Put the baking soda samples in the balloons and stretch over the bottle so that the opening is covered by the mouth of the balloon. 4. Lift the balloon and let the baking soda fall into the bottle. 5. When the reaction is complete, use the string and meter stick to measure the circumference of the balloon. Chemistry End of Year Cornerstone Assessment Key Version 1 1

2 7. Create a data table that can hold all the data you would gather through your procedure. Bottle # Amount of vinegar (ml) Amount of baking soda (g) Circumference of balloon after reaction (cm) Optional Chemistry End of Year Cornerstone Assessment Key Version 1 2

Chemistry End of Year Cornerstone Assessment: Part B. Data Interpretation and Analysis and Scientific Reasoning Directions: Read the paragraph below and review the data table.

3 Chemistry End of Year 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 setting up five plastic bottles. To each plastic bottle, she adds 10 milliliters of vinegar. She then measures out the following amounts of baking soda: 1.0g, 2.0g, 3.0g, 4.0g, and 5.0g. She pours each amount of baking soda into a different balloon and fastens the balloons over the openings of each of the plastic bottles. To initiate each reaction, she pours the baking soda out of the balloon and into the bottle. As the reactions proceed, carbon dioxide is released and fills the balloons. A picture of the setup is shown below. Once each balloon stops inflating, Patty uses a string to measure the circumference of the balloon around the widest part, and then Patty measures the length of the string that stretched around the balloon. Patty records her data in the table below. Bottle # Amount of vinegar (ml) Amount of baking soda (g) Circumference of balloon after reaction (cm) Calculate the number of moles of baking soda that were added in the first trial. The chemical formula of baking soda is NaHC0 3 (1mol = 84g). 1.0g 1mol X 84.0g X = 0.012mol (keep 2 sig. dig.) Chemistry End of Year Cornerstone Assessment Key Version 1 3

4 2. Create a graph showing the relationship between the amount of baking soda added and the circumference of the each balloon. Graph the data on the grid below. Be sure to label and correctly scale the axes and give the graph a title. Cir cu mf ere nce of Ball oo n (c m) Effect of Amount of Baking Soda on Co 2 Produced Mass of Baking Soda (g) 3. What can you interpret from the data? Specifically, relate how the amount of baking soda affects the amount of gas released. Explain your answer using the data. The more baking soda used, the greater the circumference of the balloon, so the greater the CO 2 produced. It does appear, however, that there is a point where adding more baking soda did not increase the amount of CO Suppose Patty set up a sixth trial with 10mL of vinegar and 6.0g of baking soda. Give an appropriate prediction of the circumference of the balloon for that trial. Explain your answer using the data. About 31.9cm circumference. There was little increase in circumference between 4.0g and 5.0g of baking soda, so I expect at 6.0g the circumference will not change. Chemistry End of Year Cornerstone Assessment Key Version 1 4

5 5. Patty hypothesized that increasing the amount baking soda in the reaction would produce more carbon dioxide. Based on this experiment, do you accept or reject her hypothesis? Explain your decision. I accept the hypothesis that increasing the baking soda increases CO 2, but 4.0g in 10mL of vinegar appears to be the limit for CO 2 production. More than 4.0g does not produce more CO When Patty completed her experiment, she realized that the bottle for the first trial was smaller than the other four bottles. How would this affect her measurement for trial #1? Explain your answer. If the bottle in trial 1 was smaller, the circumference of that balloon would be larger because the volume of the bottle is smaller. The CO 2 that forms will fill the balloon making a larger circumference. Chemistry End of Year Cornerstone Assessment Key Version 1 5

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