Chemical Treatment of Organic Molecules with Chlorine Lab
Testable Research Question: What is the effect of chlorine dosage (concentration) on organic
molecules?
Background:
Chlorine, in the form of hypochlorite (OCl-) can be an
effective treatment of bacterially contaminated water, and
was produced for our purposes using an SE200
Electrochlorinator (Cascade Design Inc.).
The SE200
produces a 200ml hypochlorite solution that can effectively
treat 200L; therefore the recommended dosage is 1µl
chlorine solution per 1ml of water to be treated. Chlorine
inactivates bacteria (prevents bacterial growth) by
negatively affecting bacterial processes, such as respiration
(decreases oxygen utilization), damages cell wall and membrane, and decreases levels of DNA
synthesis. There are several variables or factors that determine the effectiveness of chlorine
on bacterial inactivation. These variables include temperature, pH, contact time, turbidity,
and chlorine concentration. In this lab we will use food coloring (organic molecule) to
simulate bacteria. For the purpose of our experiment we chose to determine the effect of
increased chlorine concentration (number of doses) on organic molecules.
Hypothesis: If chlorine concentration (dosage) is increased then ___________________________
because _________________________________________________________________________.
Variable: For this experiment, what are the independent and dependent variables?
 Independent (Manipulated, Changed) Variable: __________________________________

Dependent (Responding, Measured) Variable: ____________________________________
Materials:
 SE200 Electrochlorinator
 Stock solution of blue food color
 500 ml beaker
 100 ml beaker
 Spectrophotometer
 Cuvette
 Pasteur pipette
 Timer
Procedure:
1. Prepare 200ml of chlorine using the SE 200 Electrochlorinator. The amount of
chlorine recommended per sample was determined using the formula:
a. Sample size 200ml/200L = dose amount for 200 ml water sample, which is .2ml
or 2 drops (recall 10 drops = 1 ml)
2. Prepare the food coloring solution by adding 1 drop of food coloring to 500ml of water.
3. Warm up the spectrophotometer and review the protocol for the spectrophotometer.
4. Measure 50 ml of the stock blue food color into a beaker
5. With the Pasteur pipette, fill the cuvette and read the Transmission on the
spectrophotometer. Record your reading in the table below.
6. Put 5 drops of the chlorine into the 50 ml beaker of stock blue food coloring. Precisely
record the time. This is “time 0”.
7. Using the Pasteur pipette, fill the cuvette and read the Transmission on the
spectrophotometer. Record your reading in the table below.
8. Leave the solution in the cuvette.
9. Wait 2 more minutes (2 minutes from “time 0”) and then read the Transmission on the
spectrophotometer. Record your reading in the table below.
10. Wait 2 more minutes (4 minutes from “time 0”) and then read the Transmission on the
spectrophotometer. Record your reading in the table below.
11. Wait 2 more minutes (6 minutes from “time 0”) and then read the Transmission on the
spectrophotometer. Record your reading in the table below.
12. Wait 2 more minutes (8 minutes from “time 0”) and then read the Transmission on the
spectrophotometer. Record your reading in the table below.
13. Wait 2 more minutes (10 minutes from “time 0) and then read the Transmission on the
spectrophotometer. Record your reading in the table.
Data:
Your Team’s results
Effect of Chlorine Contact Time on Transmission
Contact time (minutes)
Transmission reading with
(x axis)
Spectrophotometer at
0
2
4
6
8
10
Transmission X 100
(y axis)
Class results (represents multiple repeats of the lab
Effect of Chlorine Contact Time on Transmission at 627.5nm
Contact time
(minutes)
Transmission reading with Spectrophotometer at 627.5nm
(x axis)
Team #
1
2
3
4
5
6
7
8
9
Average
0
2
4
6
8
10
Analysis :
1. Describe your results. How do your results compare to those of the rest of the
class?
2. Take the class average for each time point on the data table.
3. Graph the class results with the contact time on the x axis and the Transmission X
100 on the y axis.
4. Explain what the graph tells you.
Conclusion:
Address the following in your conclusion:
 Restate your hypothesis. Was it correct? Why or why not?
 What did you learn from this lab? What are three Big Ideas or take away
messages? How do you know? What is the evidence from the lab that gave
you these ideas?
 Discuss any possible sources of error
 Think of a new question that can be proposed or a new variable that can be
tested.
 Wrap up with a concluding sentence summarizing this lab.