Student Experiment 2 - Particle Size and Rate of Reaction

The rate of a chemical reaction is affected by the physical size of the reactants. Decreasing the size of the particles which make up a given weight will increase the number of particles represented by the same weight. Smaller particle size results in an increase in the rate of reaction because the surface area of the reactant has been increased.

My predictions:

The powder will react _______ times faster than the whole tablet.

Materials

Note: All experiments should be done using original formula effervescent Alka-Seltzer.

3 Clear glasses
3 Alka-Seltzer tablets
Mortar and pestle
Stopwatch

Procedure

A. Whole Tablet

1. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.

2. Drop 1 whole Alka-Seltzer tablet into the water. Measure and record the time to dissolve.

B. Tablet Broken into ~8 Pieces

1. Place 1 Alka-Seltzer tablet onto a sheet of paper and break into approximately 8 pieces of about equal size.

2. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.

3. Slide broken tablet into the water from the sheet. Measure and record the time to dissolve.

C. Powdered Tablet

1. Place 1 Alka-Seltzer tablet into mortar and grind to a fine powder.

2. Transfer powder into a clear cup. (Note: It's important to have the powder in the cup before adding water.)

3. Add 8 oz. of water to the glass. Measure and record the time to dissolve.

Observations

Particle Size Time for Reaction to be Completed

Whole Tablet _________ Seconds

8 Pieces _________Seconds

Powder _________Seconds

Summary

a) As particle size decreases, the rate of reaction _______________.

b) The rate of reaction for the powder was ___________ times faster than for the whole tablet.

Questions

1. As particle size decreases, the total surface area of a reactant ________________. As a result, the probability of interactions between atoms/ions ________________, and the rate of reaction ___________________.

2. Particle size appears to have _______________ (less or more) of an effect on the rate of reaction than temperature.