Lab #27: The Effect of Concentration on Reaction Rate
Purpose – to see how concentration affects reaction rate
Experiment –
Solution 1
& water
pipet 5 mL of solution 2
Pour the contents of one test tube into the other and begin the timer.
Swirl the test tube consistently.
Stop the timer once a noticeable reaction takes place.
Repeat for various concentrations (see table)
TRIAL
Volume of
Solution 1 and H2O
Volume of
Solution 2
1
5 mL +
5 mL
5 mL
2
4 mL +
6 mL
5 mL
3
3 mL +
7 mL
5 mL
4
2 mL +
8 mL
5 mL
Reaction
Time(sec)
Analysis:
• Properly graph your data
Results: Write a statement that includes how reaction
rate is effected by the concentrations…make sure to
include actual data to support your statement.
How the Iodine Clock Reaction Works (no notes!)
STEP 1: Rate-determining step
3HSO3- + IO3sol. 1
+
sol. 2
3H2O  3SO4-2
water
+
I-
3H3O+
+
colorless ions
STEP 2:
IO3-
+
5I-
+
sol. 2
6H3O+ 
3I2 +
dark blue
9H2O
STEP 3:
I2 +
dark blue
HSO3sol. 1
+
4H2O  2I-
+
SO4-2
+
3H3O+
colorless ions
As long as there are HSO3- ions in the test tube that can
react with the I2, no visible color change will occur.