Student Learning Objectives:
Analyze factors that affect the rate at which a chemical reactions progress, and determine whether the combined substances result in a chemical reaction or a mixture.
Materials:
Apple & Air
1 Fresh Red Apple (per group) 1 Kitchen Knife
1 Vitamin C Tablet (ascorbic acid) Mortar and Pestle
Petri Dish Bubbling Potato
Hydrogen Peroxide (H2O2) Slice Potato (1/2 inch thick) Graduated Cylinder
Better Faster
2 Alka-Seltzer Tablets Mortar and Pestle 2 Thermometers Making Kool-Aid Heat Source Beaker Tongs Heat Gloves
Aluminum Foil (for lid) 2 Sugar Cubes
2 Packages Dry Kool-Aid Weak or Strong
Baking Soda 2 3-oz paper cups Vinegar (acetic acid) Triple Beam Balance Grease Pencil
Mortar & Pestle licensed under CC0
Petri Dish licensed under CC0
Notes:
• Use a Red Delicious apple
• Each team will need a total of four 250 mL beakers
• Each team will need two plastic spoons
• Materials for each mini-experiment may be placed together in stations
190 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s Introduction:
Chemical reactions may occur seemingly instantly, or may take some time to progress. There are several factors that determine the rate at which a chemical reaction occurs. In general, the more energetic and numerous collisions are between reactants, the faster reactions occur.
Sometimes reaction rates are intentionally slowed or inhibited. Factors that may affect reaction rates include nature of reactants (complexity), temperature, concentration, surface area, and use of a catalyst.
Pre-Lab:
What is a catalyst?
Which has more surface area, a solid tablet or a crushed one?
Warning: Please be careful with the knife and be aware at all times of its location.
Procedures:
You will witness a variance in reaction rates related to differing chemical factors.
Apple & Air
1. Start a list in which to record your observations.
Experiment Fastest Rate Indicator(s) Apple & Air
2. Use the mortar and pestle to crush a vitamin C tablet. Transfer the crushed contents to the petri dish and add enough water to make a paste, using a plastic spoon to mix the water with the vitamin C.
3. Cut open the apple, and immediately cover the entire surface of one half with the vitamin C paste. Leave the other half of the apple uncovered in the open air. Set both halves of the apple aside for 30-60 minutes, and proceed with the other mini-experiments while you are waiting.
4. After 30-60 minutes have passed, rinse off the vitamin C, and compare the apple halves.
Determine and record the apple that exhibited the fastest rate of reaction. List any
191 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s
indicators of chemical change; if there were no indicators of chemical change then write
“none”.
Clean-up:
• Wash and dry your mortar and pestle, petri dish, and plastic spoon Bubbling Potato
5. Obtain two 250-mL beakers, and use the graduated cylinder to add 100 mL of hydrogen peroxide to each of the beakers.
6. Add a 1/2 inch thick slice of potato to one of the beakers of hydrogen peroxide. Set the beakers side-by-side and view the beakers every few minutes for 30-60 minutes. Hydrogen peroxide (H2O2) will naturally decay to water, and your goal is to observe if the potato alters the natural reaction rate. The beaker which shows more gas bubbles is releasing oxygen atoms at the faster rate. Proceed with the other mini-experiments while you continue to check the reaction rates of the hydrogen peroxide.
7. After 30-60 minutes have passed, determine and record which hydrogen peroxide exhibited the fastest rate of reaction. List any indicators of chemical change; if there were no
indicators of chemical change then write “none”.
Clean-up:
• Rinse the graduated cylinder and set aside Better Faster
8. Fill two 250-mL beakers with 150 mL of cold water, and measure the temperature.
9. Use the mortar and pestle to completely crush one Alka-Seltzer tablet; leave the other tablet whole. At exactly the same time, add the crushed tablet to one beaker and the whole tablet to the other beaker. Stir each beaker at the same rate until the contents are dissolved, while holding the thermometer steady; do not use the thermometer for stirring.
10. Record whether the crushed tablet or the whole tablet exhibited the fastest rate of reaction. Determine whether there was a temperature change and list any indicators of chemical change; if there were no indicators of chemical change then write “none”.
192 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s Clean-up:
• Wash and dry your mortar and pestle, beakers, thermometers, and plastic spoons Making Kool-Aid
11. Fill two 250-mL beakers with 150 mL of cold water.
12. Place one of the beakers on the heat source and heat the water to nearly boiling; you may use foil as a lid to speed up the heating process. Turn off the heat source once the water is hot, and use beaker tongs or heat gloves to set the hot beaker on the table.
13. Simultaneously add one sugar cube to each beaker. Stir each beaker at the same rate until all sugar is dissolved. Record whether the hot or cold water exhibited the fastest rate of
reaction. List any indicators of chemical change; if there were no indicators of chemical change then write “none”. Then simultaneously add one package of Kool-Aid to each beaker and observe; do not stir. Record whether the hot or cold water exhibited the fastest rate of
reaction. List any indicators of chemical change; if there were no indicators of chemical change then write “none”.
Clean-up:
• Wash and dry your beakers and plastic spoons Weak or Strong
14. Label one beaker 100% and the other beaker 50%, with the grease pencil.
15. Use the graduated cylinder to add 100 mL of vinegar to the “100%” beaker. Then add 50 mL of vinegar and 50 mL of water to the “50%” beaker.
16. Measure 5 grams of baking soda into each paper cup.
17. Place both beakers in a sink. Then simultaneously add 5 grams of baking soda, from the paper cups to each beaker. Record whether the “100%” or “50%” solution exhibited the fastest rate of reaction. List any indicators of chemical change; if there were no indicators of chemical change then write “none”.
Clean-up:
• Throw away apple, potato, and paper cups
193 | P h y s i c a l S c i e n c e L a b o r a t o r y I n v e s t i g a t i o n s
• Thoroughly wash and completely dry all glassware, plastic spoons, and other re-usable items (place graduated cylinder on drying rack to air dry)
• Clean your lab table
Analysis:
1. In which case was the reaction rate slowed or inhibited?
2. What item or substance was added to be a catalyst?
3. In general, does a high temperature or a low temperature increase the reaction rate?
4. What is the purpose of crushing a tablet, what factor in reaction rates does this increase?
5. How did the dissolving of the sugar cube compare to the Kool-Aid? Why did this happen?
6. Write a general statement regarding concentration and reaction rates.
General Questions:
1. Some labels on medications warn against braking and/or crushing tablets. Explain why crushing certain medications could be dangerous in terms of chemical reaction rates.
2. Do other fruits and vegetable turn brown when left open in the air? What do you think the brown substance is? Hint: Red Delicious apples contain a lot of iron which reacts with oxygen in the air.
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