Analysis of Laundry Bleach: An
Oxidation-Reduction Titration
Tadas Rimkus
AP Chemistry
Period 2
Background Information

Reduction-oxidation reactions describe all
chemical reactions in which atoms have their
oxidation number (oxidation state) changed.
 Oxidation describes the loss of electrons
 Reduction describes the gain of electrons
Background Information
Background Information

Titration is a
common laboratory
method that is used to
determine the
unknown
concentration of a
known reactant.

A reagent, called the
titrant, of a known
concentration (a
standard solution)
and volume is used to
react with a solution
of the titrand, whose
concentration is not
known.
Objectives

SWBAT:



Calculate the percentage of bleach in common
bleach products.
Learn to complete titration labs
Learn about reduction-oxidation reactions
Reactions

You will add an excess of potassium iodide (KI) to an
acidified sample of laundry bleach. The NaOCl in the
bleach oxidizes the I- ion to I2. The amount of I2
produces is directly related to the original amount of
NaOCl (or OCl- ions) present in the bleach:
2I- + OCl- + 2H+
I2 + Cl- + H2O
Reactions

You will titrate the I2 produced in Reaction 1
with a standardized solution (known molarity)
of sodium thiosulfate (Na2S2O3) as the titrant.
Thiosulfate ion reduces the I2 ion to I- ion by the
following redox reaction:
I2 + 2S2O3

2I- + S4O62-
The indicator is starch solution, which forms an intensely blue
complex with I2. This color vanishes at the end point when the last
trace of I2 is reduced.
Materials











Commercial laundry bleach
KI, 2M
Acetic Acid, 6M
Na2S2O3 5H2O
Starch indicator, 1%
500-mL Volumetric flask
Stirring rod
Funnel
50-mL buret
250-mL beaker
Distilled water
Procedures
1.
2.
Rinse and fill your cleaned buret using
the sodium thiosulfate solution
(Na2S2O3). Record the initial volume to
the nearest 0.01 mL.
Clean and rinse a 250-mL Erlenmeyer
flask with distilled water. Dry the outside
and weigh to the nearest milligram.
Procedures
1.
2.
Add 2.0-2.5 mL of
bleach to the
weighed flask
(remove flask from
scale before adding
bleach)
Reweigh the flask to
the nearest
milligram.
www.clorox.com
Procedures
5.
Immediately after second weighing, add 100
mL of distilled water (pour it down the sides of
the flask to wash down any bleach drops)
www.npwd.org
www.merriam-webster.com
school.discoveryeduc
ation.com
5.
6.
Measure out 10 mL of dilute (6 M) acetic acid
(HC2H3O2) and 8 mL of 2 M KI
Add the acetic acid to the flask, swirl, and then
add the KI solution and swirl.
upload.wikimedia.org
vitaminsbeautycare.com
www.merriam-webster.com
Procedures
8.
9.
10.
11.
Titrate promptly by slowly adding titrant from
the buret, swirling the flask constantly.
When the solution has changed to a gold-orange
and then to a faint yellow color, add 20 (1 mL)
drops of starch indicator to turn the solution
blue.
Rinse the inside surface of the flask with
distilled water.
Place a piece of white paper under the flask and
continue to titrate until the blue color just barely
disappears.
Procedures
1.
2.
3.
4.
5.
Record the final buret reading.
In your notebook, calculate the ration R =
(Volume of titrant delivered)/(Mass of bleach)
in units of mL/g.
Refill the buret, record the buret reading, and
titrate an additional bleach sample following the
steps above.
Calculate R for the new titration
When finished, drain the volumetric flask and
buret and rinse.
Results
Mass of Na2S2O3 2.40 g
Bleach brand name Clorox Bleach
Solution 1
Solution 2
Mass of Bleach (g)
2.39 g
2.42 g
Volume of titrant delivered
34.36 mL
34.51 mL
Molarity of thiosulfate solution
.9710 M
.9714 M
Moles of Sodium Thiosulfate used
.09710 mol
0.09714 mol
Moles of Iodine reduced
.007 mol
.0082 mol
Moles of NaOCl in sample
.0312 mol
.0327 mol
Mass of NaOCl in sample
2.322 g
2.434 g
Percent NaOCl by mass
12.37%
12.51%
Conclusion
By calculating the two percentages of the
bleach samples, we got 12.37% and
12.51% bleach by mass for Solution 1 and
2 respectively. This completed our first
objective. And by completing this
experiment, we learned how to do
titrations and learned about oxidationreduction reactions.