Name: _____________________________
Lab Investigation: Factors that Affect Reaction Rate
Introduction:
You may have noticed that chemical reactions occur at different rates. The explosion of
fireworks is instantaneous; the rusting of an iron gate is relatively slow. A rate is measure of change
per unit time. For example, the rate of change of distance over time is called speed. The rate of a
chemical reaction is studied in terms of changes in concentration of a reactant or product over time.
Chemists study rates of reaction in order to control the progress of a chemical reaction. In
order to understand how the rates of chemical reactions can be controlled, it is necessary to
understand the factors that influence the rates of chemical reactions.
In this experiment, you will study the effect that temperature and particle size have on the rate
of a chemical reaction.
Materials:
Alka-Seltzer (Kroger brand) tablets
stop watch
fork
Vinegar
one Erlenmeyer flask
water (cold, warm)
piece of paper
scissors
Procedure:
1. Put on safety goggles.
2. Obtain a packet of Alka Seltzer tablets. Divide the two tablets into four equal portions (i.e. break
each in half using the scissors.
3. Obtain 100 mL of warm-hot water from the sink.
4. Obtain half of an Alka-Seltzer tablet and prepare to start timing.
5. Drop the tablet into the water and begin timing.
6. Stop timing once the reaction has visibly slowed down (no more gas produced).
7. Record the reaction time. Rinse content of beaker down drain.
8. Repeat steps #3-7 using cold water.
9. Obtain half of an Alka-Seltzer table and place on the piece of paper (paper folded at sides).
10. Grind the tablet into a fine powder using the fork.
11. Obtain 100 mL of cold tap water in an empty Erlenmeyer flask. Record its temperature.
12. Empty the powdered tablet into the water and begin timing. Stir gently with the handle end of the
fork to keep the powder from floating on the surface. Stop timing when the reaction slows down.
13. Measure 100 mL of vinegar into an empty Erlenmeyer flask.
14. Obtain half of an Alka Seltzer tablet and prepare to start timing.
15. Drop the tablet into the water and begin timing.
16. Stop timing once the reaction has visibly slowed down (no more gas produced).
17. Record the reaction time. Rinse content of beaker down drain.
18. Clean the Erlenmeyer flask using water. Clean laboratory station and leave materials at the lab
station on the counter.
(continued on back)
Data:
Reaction
Reaction Time (seconds)
Warm Water
Cold Water
Powdered Tablet
Tablet with Vinegar
Conclusions: Answer each of the following in complete sentences.
(1) Write the balanced chemical equation for the reaction studied:
sodium bicarbonate (CHNaO3) + citric acid (C6H8O7) yields sodium citrate (NaC6H7O7), carbon dioxide
(CO2), and water (H2O)
(2) How does temperature affect the rate of a reaction (i.e. does an increase in temperature make the
reaction go faster or go slower)? Discuss your results for cold and warm water.
(3) By grinding the tablet, we increased the exposed surface area. What effect did this have on the
rate of the reaction (faster or slower)? Why?
(4) When you added additional acid (vinegar) to the reaction, what effect did this have on the rate of
the reaction (faster or slower)? Why?
(5) Using your data, complete the following statements with either the word “increase” or “decrease”.
1. To increase the rate of a reaction, you should ________________ temperature.
2. To increase the rate of a reaction, you should ________________ surface area.
3. To increase the rate of a reaction, you should ________________ concentration.