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Understand factors that affect the rates of chemical reactions - temperature, concentration of reacting substances in solutions, surface area (particle size) of solids in reactions with gases and liquids, and catalysts.

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Introduction

VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE GTF Rates of Chemical Reactions Fall 2003 GOAL To understand factors that affect the rates of chemical reactions - temperature, concentration of reacting substances in solutions, surface area (particle size) of solids in reactions with gases and liquids, and catalysts. OUTLINE I. Introduction, p. 2 Gives overview of experiment. II. Demonstrations of Effect of Surface Area, p. 3 You give two demonstrations of the effect of surface area. A. Dust in a flame, p. 4 - Spray lycopodium powder into the flame of the tea candle. This produces a large flame because of the rapid burning of the lycopodium powder due to its small particle size and therefore its large surface area that is exposed to the oxygen in the air. B. Dust can explosion, p. 4- Spray lycopodium powder into the can where the flame of the tea candle causes the same rapid burning of the lycopodium powder you demonstrated in Part A. The large volume of combustion gases (carbon dioxide and water vapor) builds up enough pressure to blow off the lid of the can. III. Effect of Surface Area , p. 6 Students observe how fast bubbles of carbon dioxide are produced when vinegar is added to a whole piece of chalk and a crushed piece of chalk. The bubbles are produced faster with the crushed chalk than with the whole piece. IV. Effect of Temperature, p. 6 Students observe how fast bubbles of carbon dioxide are produced when room-temperature vinegar and warm vinegar are added to chalk. The bubbles are produced faster in the warm vinegar than in the room-temperature vinegar. V. Effect of Concentration, p. 7 Students observe the different rate of carbon dioxide bubbles produced when two different concentrations (100% and 50%) of vinegar are added to chalk. The stronger solution produces bubbles at a faster rate. VI. Catalysts, p. 8 Students observe the effect of a catalysts on the rate of decomposition of hydrogen peroxide by seeing the bubbles of oxygen produced when manganese dioxide and a potato slice is added to hydrogen peroxide. ...read more.

Middle

Use a match to start the twigs. These ignite easily and create enough heat to ignite the larger pieces of wood. This illustrates the effect of surface area or particle size on the rate of reaction - the smaller the pieces of wood, the more surface area is exposed to the oxygen in the air. III. EFFECT OF SURFACE AREA (PARTICLE SIZE) MATERIALS - use test tubes "A" and "B" 2 test tubes with 10 ml regular vinegar at room temperature 2 pieces (1/8ths of a stick) of chalk 1 snack bag 1 textbook for crushing chalk (students provide) 1 pair of scissors 1 funnel � Ask students to use what they learned about surface area in the last experiment to suggest ways to increase the surface area of the tablets to speed up the rate of the reaction. Accept logical responses and ask students to explain their answers. Have each group do the following: � Take one of the pieces of chalk, put it in the snack bag and crush to a fine powder by tapping on the bag with a textbook. � Insert the funnel into test tube "B". � Ask students to observe the two pieces of chalk now and tell which piece has more surface area. (The crushed chalk - more of the inside surface of the chalk is now exposed.) � Shake all the crushed chalk into one bottom corner of the bag and cut the other bottom corner off. Then pour the crushed chalk through the bottom cut corner into the test tube "B" through the funnel. � Put the other piece of chalk into test tube "A". � Observe what happens and record observations. Ask students, Which piece of chalk produced a faster reaction? Why? (Bubbles of carbon dioxide come off more quickly from the crushed chalk than from the whole piece.) Ask students, How does this illustrate the effect of surface area or particle size on the rate of a reaction? ...read more.

Conclusion

3. Take test tube "D" and place in hot water until it is ready to use in Part IV. 4. Measure 5 mL of vinegar and pour into test tube "F". Measure 5 mL of water and pour into test tube "F". This is your 50% vinegar solution. 5. Measure and pour 10 mL hydrogen peroxide into test tubes "G, H and I". B. EFFECT OF SURFACE AREA - USE TEST TUBES "A" AND "B". 1. Demonstration with lycopodium powder. 2. Experiment: � Take one of the pieces of chalk, put it in the snack bag and crush to a fine powder by tapping on the bag with the CAPPED vinegar bottle textbook. � Insert the funnel into test tube "B". � Shake all the crushed chalk into one bottom corner of the bag and cut the other bottom corner off. Then pour the crushed chalk through the bottom cut corner into the test tube "B" through the funnel. � Put the other piece of chalk into test tube "A". � Observe what happens and record observations. C. EFFECT OF TEMPERATURE - USE TEST TUBES "C" AND "D". � Remove test tube "D" from the warm water and place in your rack. � Add one piece of chalk to test tube "C" and one to "D". � Compare the rate of CO2 gas bubbling off (i.e., the rate of bubbles being produced) and write down your observations. D. EFFECT OF CONCENTRATION OF A SOLUTION - USE TEST TUBES "E"AND "F" � Place a piece of chalk in the 100% and 50% vinegar solutions and observe closely to see the results. � Record observations. E. EFFECT OF A CATALYST - USE TEST TUBES "G, H AND I" � Observe the hydrogen peroxide (test tube "I") to see that nothing is happening. � Place a small scoop of manganese dioxide in test tube "G" and a sliver of potato in test tube "H". � Observe what happens and record observations. Compare with test tube "I". Chalk Rates Chalk Rates 2 1 ...read more.

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