Lab Activity #1: Rates of Reaction Lab (a.k.a. Iodine Clock Reaction)
Kandace Little
Teacher Information:
Course: Chemistry 30
Unit: Reaction Kinetics
Curriculum fit:
Objective: Examine the factors which influence reaction rates in the context of
the collision theory
CEL: Treat themselves and others with respect. Work cooperatively and
contribute positively in group learning activities.
Indicators:
1) Identify some factors which affect the rate of chemical reactions
2) Apply collision theory to account for the factors which affect the rates of
chemical reactions.
New knowledge being introduced: If done at the beginning of the unit, this lab will introduce
them to how reaction rates are affecting by concentration and temperature. If you decide to give
them the pre-lab reading, they will also be introduced to the 5 factors affecting reaction rates.
What happens? In both parts of this lab, 2 clear solutions are mixed together and they turn a
blackish-blue color. In part A, students alter the concentration of the 2 solutions and time how
long it takes the two solutions to turn color. In part B, students alter the temperature and time
how long it takes the two solutions to turn color.
Things to look out for:
-The lab works best when you set up the equipment for the students beforehand so the data
collection goes quicker
-Make sure you make solution A and solution B the same day the students are doing the lab
-Make sure they don’t mix their thermometers!
-Data collection goes faster if they have 2 people doing Part A and 2 other people doing Part B,
then swap data
-Temperature (Part B) takes longer than concentration. Have water on hot plates prior to class so
they can start with the 450C trial first.
Connections: Students should already know what the Collision Theory is as well as what a
Reaction Rate is. Students should be able to make the connections between this lab and those 2
things.
Disclaimer: This lab activity is fairly structured (including a purpose, hypothesis, data table,
procedure, etc.) but you can structure this to be a more inquiry-based activity by providing
students with even less information before they try the lab. You could also try not having a “set”
procedure for them to follow and just ask them to “go find out how temperature and
concentration affect a reaction rate.”
Making the Solutions:
Solution A: dissolve 4.3g of potassium iodate (KIO3) per liter of solution to produce a 0.02 M
solution.
Solution B: dissolve 2 g of sodium bisulfite (NaHSO3), 5 mL 1.0 M H2SO4, and 4 g soluble
starch per liter of solution. (Solution B can also be made from sulfurous acid and soluble starch)
**note: alter the amount of each solution you make based on class size
Pre-Lab Reading:
The rate of a chemical reaction is the time required for a given quantity of reactants to be
changed to product. Reaction rate usually is expressed in terms of moles per unit time. This rate
is affected by several factors, including the nature of reactants, concentration of the reactants,
temperature, pressure, and the presence of catalysts. In this experiment, you will study the
effects of temperature and concentration.
A chemical reaction is the result of effective collisions between particles of reactants.
Increasing the temperature of a system raises the average kinetic energy of the particles of the
system. This results in more collisions and, of greater importance, more effective collisions per
unit time. This affects the rate of the reaction.
At constant temperature, increasing the concentration of one or more of the reactants
increases the number of particles present and, hence, the number of collisions. This affects the
rate of the reaction.
In this experiment, two solutions will be mixed, and the completion of the reaction will
be marked by a color change. One solution contains the iodate ion (IO3-). The other contains the
hydrogen sulfite ion (HSO3-) and soluble starch. The entire reaction takes place in two stages.
The ionic equations for these stages are:
1. IO3- (aq) + 3HSO3- (aq)  I-(aq) + 3SO42- (aq) +3H+ (aq)
2. 5I- (aq) + 6H+ (aq) + IO3- (aq)  3 I2 (aq) + 3 H2O (l)
In the presence of starch molecules (not shown), molecular iodine (I2) produced a characteristic
blue color. The rate of the entire reaction can be determined by timing the interval between the
time the two solutions are mixed and the appearance of the blue color. By varying the
concentration of one of the reactants (at constant temperature) and then varying the temperature
along, you can observe and record the effects of these two factors on reaction rate.
This experiment should provide a better understanding of reaction rates and the factors
that affect these rates.
Purpose:
Study the effect that changing the concentration of a reactant has on the rate of a
chemical reaction. Study the effect that changing the temperature has on the rate of a chemical
reaction. Formulate hypotheses about how reaction rates are affected by changes in temperature
and in concentration of reactants.
Materials: (for each group)
-250 mL beaker
-timer/stop watch with second hand
-100 mL beakers (4)
-safety goggles
-10 mL graduated cylinders (2)
-lab apron or coat
-medium size test tubes (2)
-thermometer
-Solution A (with IO3 ion)
-distilled water
-Solution B (with HSO3- ion and soluble starch)
-ice cubes
Safety:
Avoid spilling reagent solutions on your skin or clothing. Wash off any spills
immediately with cold tap water. Always wear safety goggles and a lab apron or coast when
working with chemicals.
Procedure:
Part A
1. Using a clean and dry 10 mL graduated cylinder, measure exactly 10.0 mL of Solution A and
pour it into a 100 mL beaker.
2. Using a second 10 mL graduate, measure exactly 10.0 mL of Solution B and pour it into
second 100 mL beaker.
3. Prepare to time the reaction. While one lab partner pours Solution A into Solution B, the
second partner should immediately start timing the reaction. Pour the solutions back and forth
several times from one beaker to the other to ensure thorough mixing. Then allow the mixture to
stand. At the instant a color change occurs, the partner timing the reaction should note the
elapsed time. Record this in your data list. Rinse and dry the beakers and graduated cylinders.
4. Measure exactly 10.0 mL of Solution B into one of the beakers. Using a clean graduated
cylinder, measure exactly 9.0 mL of Solution A into the other beaker. Dilute this solution by
adding exactly 1.0 mL of distilled water. Follow the step 3 instructions for mixing the solutions
and timing the reaction. Record the elapsed time in your data list. Rinse and dry the beakers and
graduated cylinders.
5. Repeat step 4 four more times, using increasingly dilute samples of Solution A. Use the
following ratios of Solution A to distilled water (in mL): 8 to 2; 7 to 3; 6 to 4; and 5 to 5. Rinse
and dry the beakers and graduated cylinders after each trial. Record elapsed times in Part A of
“Observations”.
Part B
1. Measure 10.0 mL of Solution A into one test tube and 10.0 mL of Solution B into a second
test tube.
2. Half fill a 250 mL beaker with cold tap water. Add ice cubes to the water and stir carefully
with the thermometer. Continue stirring (and adding ice as needed) until the temperature of the
ice-water mixture is about 5 0C.
3. Place the two test tubes in the ice-water bath and let them stand until the solutions are at the
same temperature as the ice water. Always rinse and wipe the thermometer after removing it
from a solution.
4. When the solutions are at the same temperature as the ice water, prepare to time the reaction.
One lab partner should start timing the reaction the instant the second partner pours Solution A
into Solution B. Quickly pour the mixture back and forth from test tube to test tube several times
and return the mixture to the ice-water bath. At the instant a color change occurs, note the time
elapsed. Measure the temperature of the mixture immediately. Record the exact temperature
and elapsed time in your data table. Discard the mixture as instructed. Rinse and dry the test
tubes.
5. Repeat step 1.
6. Prepare a water bath at a temperature of about 150C. Repeat steps 3 and 4 are this new
temperature. Record your observations in your data table.
7. Repeat these procedures using warm baths at the following temperatures: 250C; 350C; 450C.
Use warm tap water to prepare these baths. Rinse and dry the test tubes after each trial.
Name: ______________________
Partner(s): __________________________
Rates of Reaction Lab
Purpose:
 Study the effect that changing the concentration of a reactant has on the rate of a
chemical reaction.
 Study the effect that changing the temperature has on the rate of a chemical reaction.
 Formulate hypotheses about how reaction rates are affected by changes in temperature
and in concentration of reactants.
Hypothesis:
1) As concentration of reactants increases, the reaction rate will _________________.
2) As temperature of reactants increases, the reaction rate will __________________.
Materials and Procedure: SEE HANDOUT
Observations:
PART A
Solution B (mL)
10
10
10
10
10
10
Solution A (mL)
10
9
8
7
6
5
Water (mL)
0
1
2
3
4
5
Time (sec)
PART B
Trial #
1
2
3
4
5
Temperature (0C)
50C
150C
250C
350C
450C
Time (sec)
Reaction time (sec)
Reaction time (sec)
Calculations:
1) Plot your data from Part A on the grid provided. Draw a line through the plotted points
to produce a best fit line showing the effect of concentration of reactants on reaction rate.
2) Plot your data from Part B on the grid provided. Draw a line through the plotted points to
produce a best fit line showing the effect of temperature on reaction rate.
Discussion/Conclusions:
Before answering the following questions, think carefully about the difference between reaction
rate and time. If the time it takes to complete a reaction goes up (takes longer), then the reaction
rate is actually decreased (slowed down). If time decreases, then reaction rate increases.
1) Based on your experimental data, make a general statement (hypothesis) about the effect
of concentration of reactants on reaction rate.
2) Make a similar hypothesis about the effect of temperature on reaction rate.
3) From the lab reading, list 5 factors that affect the rate of a reaction.
4) A chemical reaction is the result of effective collisions between particles of reactants.
Explain in terms of the “collision theory” how both temperature and concentration of
reactants affect the rate of reaction.
Conclusion: Was your hypothesis correct? If no, what did you discover actually happened?
Pictures from when I did the lab:
Temperature
Set up
The Color
Change
Mixing Solution A
and Solution B
Materials for
Concentration
Lab Activity #2: Reaction Spontaneity Stations
Kandace Little
Teacher Information:
Course: Chemistry 30
Unit: Energy Changes in Chemical Reactions – thermochemistry
Curriculum fit:
Objective: Understand the reasons why entropy and enthalpy effects are
important
Indicators:
1) Identify how entropy effects influence chemical reactions.
2) Consider the interaction between enthalpy and entropy in determining whether
a reaction is spontaneous.
3) Use the concept of free energy to express the quantitative relationship between
entropy and enthalpy.
4) Predict spontaneity of reactions using
∆G0 = ∆H0 - T∆S0
New knowledge being introduced: Assuming the students have already been introduced to the
concept of spontaneous processes and entropy, this lab will introduce students to 5 different
scenarios where they can predict what will happen to the entropy of a system. Instead of just
giving students the answers of what would happen to the entropy in each situation, I had them
explore and experience for themselves firsthand what would happen.
What happens?
Divide the students up into groups of 4 or 5 students and have them go to the 5 stations around
the room. (I told them to just go to one because of time constraints, but you could have them go
to all stations if you would like) Students follow the directions on the station worksheet and
answer the few questions that are also on the worksheet.
Things to look out for:
-Remember to turn on the hot plates for the temperature station before class and have enough
beakers for multiple groups
-Don’t give them the answers! It’s much more rewarding watching them figure them out for
themselves. Simply walk around and monitor each station, asking prompting questions if need be
Connections:
After this lab, students would be able to make the connections between spontaneity and entropy.
You would follow up this lab activity with introducing them to Gibbs free energy because it
relates enthalpy, entropy, and spontaneity.
Things I would change for next time:
-I would actually make them worksheets for each station and then not bring the class back
together to fill out the fill-in-the-blank notes after the activity. Perhaps the notes could become
the worksheets. The way I had them do it was just answering the questions on loose leaf and
then coming back as a class to fill in the notes
-I would let each group go to each station instead of just one. This would change the format I
had of the expert group reporting back to the class, but that way everyone would get to
experience every station for themselves which would help them understand each better
-Change a couple stations to be more “hands-on”
-Take titles off of each station to make it more “discovery/inquiry” for students
Fill in the blank notes that I used before & after the activity:
Station Cards: (to be set up in different spaces around the laboratory/classroom with the
appropriate materials at each station)
1. Changes of State
You have 3 objects. One is a solid, one is a liquid and
one is a gas (in the bottle). Think about how tightly
packed the particles are in each.
Below is a diagram to help you see the particles in each of
the objects you have.
Remembering that entropy is the disorder or randomness
of the particles, which of your three states of matter
would have the highest entropy?
Write the 3 states of matter in increasing order of entropy.
2. Dissolving Gas in a
Solution
Examine the picture below. It is showing a gas being
dissolved in a solution.
Fact: The gas has high entropy (a lot of disorder).
Based on the picture and the FACT that was given to you,
what do you think happens to the entropy (disorder or
randomness) when a gas is dissolved into a solution
(water)?
Why do you think this?
3. Number of Gaseous
Particles
At this station, every group member needs to write
down the following equation on their piece of loose
leaf:
SO3(g)  SO2(g) + O2(g)
BALANCE the equation. Make sure you all have
the same answer before moving on.
Decide how many particles you have on the reactant
side and the product side (this should be your
coefficient numbers).
Knowing how many particles are on each side,
which one do you think has a higher entropy
(disorder)? The product side or the reactant side?
What statement can you make about entropy
(disorder) in regards to the number of particles?
4. Dissolving a Solid/Liquid
in a Solution
Take a look at the following picture.
The left side shows a solid. The right side shows what
happens to the particles as the solid dissolves in a
solution.
At your station, you have iced tea crystals. Mix yourself
a glass of iced tea…..but only have one glass to ensure
everyone in the class gets some.
As you drink your iced tea, come up with a statement
about what is happening to the entropy
(disorder/randomness) of the particles when you dissolve
a solid in water.
5. Temperature
Below is a picture of particles that are frozen or very
very cold.
As you can see, they don’t have very much kinetic
(movement) energy. On your piece of loose leaf, draw
what you think the particles might look like if you
increased the temperature.
Now let’s see if your drawing is correct by doing a little
experiment:
1) Take one of your beakers and fill it up with COLD
water.
2) Take the other beaker off the hot plate and set them
beside each other.
3) Using red food coloring for the hot water and blue
coloring for the cold water, put a drop in each beaker at
the same time and observe.
4) After a minute, you can add one more drop.
Which one (cold or hot) do you think has a higher
entropy? Make a statement about entropy
(disorder/randomness) in regards to temperature.
Pictures of the lab activity: