QUANTITATIVE STUDY OF REACTION RATES
INTRODUCTION:
Factors that can affect the rate of a reaction include temperature, and the concentration of
reactants. In this experiment, you will conduct some simple reactions to investigate,
quantitatively, how these factors can influence the outcome of a reaction.
In Part One, the reaction examined is that between sodium thiosulfate and hydrochloric
acid:
Na2S2O3 + 2 HCl  2 NaCl + H2O + S + SO2
The concentration of the thiosulfate will be changed by adding water and the appearance
of the opaque colloidal sulfur will be used to determine the rate of the reaction.
In Part Two, the reaction examined is the reduction of potassium permanganate by
glucose:
MnO4- + glucose  Mn+2 + CO2 + H2O
The reaction rate is determined by timing how long it takes for the purple color of the
permanganate to disappear at different temperatures.
OBJECTIVE:
To determine quantitatively how concentration of reactants, temperature and catalysts
affect the rate of a reaction.
APPARATUS AND MATERIALS:
Erlenmeyer flask, 150 ml
Burette, 50 ml
Retort stand
5 test tubes
2.0 M HCl
0.10 M KMnO4
graduated cylinder, 50 ml
burette clamp
balance
hotplate
2.0 M H2SO4
0.25 M Na2S2O3
beaker, 250 ml
thermometer
timer
test tube rack
0.10 M glucose
white paper with an X
SAFETY:
Most of the metal solutions are poisonous. Potassium permanganate can stain hands and
clothing.
Sulfuric acid and hydrochloric acid are corrosive. Avoid contact.
Wash with plenty of water if spillage occurs.
PROCEDURE:
Part 1: Effect of Change of Concentration
1. Prepare the following table in your lab notebook:
Concentration of sodium thiosulfate
20%
40%
60%
80%
100%
Time until cross disappears (s)
2. Place 10 ml of sodium thiosulfate in a 150 ml Erlenmeyer flask and add 40 ml of
water.
3. Place the flask on top of a sheet of white paper with a cross marked on it.
4. Add 5 ml of 2.0 M HCl and at the same time start the stop watch. Swirl the
contents of the flask.
5. Look vertically down the flask at the cross and record the time taken until the
cross can no longer be seen through the solution.
6. Repeat the experiment using 20, 30, 40, 50 ml of sodium thiosulfate, diluted with
water so that the total volume of 50 ml is maintained in each case before addition
of the acid. Make sure that the Erlenmeyer flask is rinsed well between reactions.
7. Clean the Erlenmeyer flask thoroughly and drain well.
Part 2: Effect of Temperature
1. Prepare the following table in your lab notebook
Temperature of Solution
Time (s)
2. In a 250 ml beaker, place 25 ml of 2.0 M H2SO4 and 75 ml of water.
3. Add 4 ml of KMnO4
4. Warm the beaker on a hot plate until the temperature of the liquid is 85-90oC.
5. Place the beaker on a sheet of white paper and record the exact temperature. Add
5 ml of glucose solution and start the timer. Swirl to mix, and record the time it
takes for the purple color to disappear.
6. Repeat the experiment, heating the beaker to a temperature 5oC below the
previous temperature used. Continue for a total of five different temperatures.
Make sure the beaker is cleaned well between reactions.
7. Clean your glassware.
Graphs:
Part One:
1. Plot a graph of your data for the concentration of thiosulfate (vertical axis) versus
time (horizontal axis)
2. Plot the concentration of thiosulfate versus the reciprocal of time (1/T). The
reciprocal of time is a measure of the rate of the reaction.
Part Two:
1. Plot a graph of temperature (vertical axis) versus time (horizontal axis)
Include in conclusion:
What is the effect on concentration on reaction rate…and an explanation
What is the effect of temperature on reaction rate…and an explanation