Vincent Kurp
Quantitative Analysis
Real World Project: The Determination of the Change in Concentration of Sodium Hypochlorite in Bleach
Purpose:
The most common active ingredient for household bleach is sodium hypochlorite. Bleach
companies report that in order to have an effective bleach solution, the weight percent of hypochlorite
has to be above at least 6%. They also report that prolonged exposure to sunlight and temperatures
above 70℉ will degrade the sodium hypochlorite, therefore weakening the product. The purpose of this
experiment was to compare the sodium hypochlorite concentrations of different brands of household
bleach, and observe how heat and sunlight exposure can affect each one differently. The brands of
bleach we studied during this experiment were White Cloud, Great Value, and Clorox. My hypothesis
was that heat exposure would have the greatest effect on the concentrations of sodium hypochlorite. I
also predicted that Clorox would undergo the least amount of change in hypochlorite concentration. I
believed this because Clorox adds in sodium chloride and sodium chlorate, which are substances that
result from the natural breakdown of sodium hypochlorite. These are added to thicken the bleach and
stabilize the formula.
Reactions:
3NaClO  NaClO3 + 2NaCl
OCl- + 2I- + 2H3O+  I2 + Cl- + 3H2O
I2 + 2S2O32-  2I- + S4O62Procedure:
Preparation:
A starch solution was made by dissolving 1g of soluble starch in 10mL of water, diluting it to
100mL, then boiling it until clear. A thiosulfate solution was made by dissolving 17.4g of Na2S2O3 in 1L of
freshly boiled distilled water containing 0.1g Na2CO3. This solution was transferred into amber bottles
for storage purposes. Another solution was prepared by dissolving 2g solid KIO3 in 1L of distilled water.
Standardization of Thiosulfate:
Three 50mL aliquots of KIO3 were transferred via pipette into Erlenmeyer flasks. To each sample
1g solid KI and 10mL 1M H2SO4 were added. Each sample was titrated with the standardized thiosulfate
solution until the pale yellow color was almost lost. Then the starch indicator was added and the
titrations were finished to a clear endpoint. This procedure was repeated for a total of three trials.
Bleach Titration Procedure:
Three 2g bleach samples were weighed out in Erlenmeyer flasks. To each sample, 10 mL distilled
water, 5mL 6M HC2H3O2 and 1g solid KI were added. Each sample was titrated with standardized
thiosulfate until the pale yellow color was almost lost. Then the starch indicator was added and the
titrations were finished to a clear endpoint. This procedure was performed for each of the three brands
of bleach to determine their initial sodium hypochlorite concentrations.
Bleach (Heat Exposure):
400 mL samples of each brand of bleach were poured into beakers, covered with watch glasses,
and stored on a warm hotplate. They were left on the hotplate for 1 week and the temperature was
recorded halfway through. After 1 week the samples were removed from the heat and allowed to cool.
All the samples were diluted back to 400mL to replace any water that had evaporated over the course of
the week. Then the Bleach Titration Procedure shown above was performed for each brand of bleach to
determine their sodium hypochlorite concentrations.
Bleach (Sunlight Exposure):
250 mL samples of each brand of bleach were poured into clear bottles, sealed, and placed on a
windowsill for 1 week where they received direct sunlight during the day. After 1 week, the Bleach
Titration Procedure shown above was performed for each brand of bleach to determine their sodium
hypochlorite concentrations.
Data:
Initial Bleach Titrations
Standardization 1
Mass Thiosulfate: 17.4137
Mass Na2CO3: 0.01137
Mass KIO3: 2.0280g
Trial
1
2
3
L KIO3
0.05
0.05
0.05
mol KIO3 used
0.000473842846795
0.000473842846795
0.000473842846795
L Thiosulfate
0.04207
0.04207
0.04207
Average
Std Deviation
M Thiosulfate
0.06757920325108
0.06757920325108
0.06757920325108
0.06757920325108
0
White Cloud
trial
1
2
3
L
Thiosulfate
used
0.03262
0.03191
0.03225
mol Thiosulfate
L
Thiosulfate
used
0.03398
0.03409
0.0345
mol Thiosulfate
mol Hypochlorite
mass
bleach
0.00220443361005 0.001102216805025 1.0182
0.002156452375742 0.001078226187871 0.9993
0.002179429304847 0.001089714652424 1.015
Average
Std Dev
Mass %
(hypochlorite in
bleach)
8.05824189413366
8.03193809918096
7.99195652477015
8.02737883936159
0.033377053277426
Clorox
trial
1
2
3
mol Hypochlorite
mass
bleach
0.002296341326472 0.001148170663236 0.9985
0.002303775038829 0.001151887519415 1.0003
0.002331482512162 0.001165741256081 1.015
Average
Std Dev
Mass %
(hypochlorite in
bleach)
8.55982215035313
8.57207907080142
8.54953488696342
8.56047870270599
0.011286423347561
Great Value
trial
1
2
3
L
Thiosulfate
used
0.02982
0.03026
0.0309
mol Thiosulfate
mol Hypochlorite
mass
bleach
0.002015211840947 0.001007605920474 1.0096
0.002044946690378 0.001022473345189 1.0077
0.002088197380458 0.001044098690229 1.024
Average
Std Dev
Mass %
(hypochlorite in
bleach)
7.42929721870587
7.55313246163111
7.59010805670508
7.52417924568069
0.084224390409702
Bleach (Heat Exposure) Titrations
Standardization 2
Mass KIO3: 1.0244
Mol KIO3: 0.000478689
Temperature of bleach: 86℉
Trial
1
2
3
L Thiosulfate Added
0.0394
0.03862
0.0385
Average
Std Dev
M Thiosulfate
0.072896856
0.074369138
0.074600938
0.073955644
0.000924233104637
Clorox
Trial
1
2
3
L
Thiosulfate
Used
0.01194
0.0121
0.0121
Bleach (g)
mol Na2S2O3
mol OCl- present
Mass % OCl-
1.0075
1.0188
1.0301
0.00088303
0.000894863
0.000894863
0.000441515
0.0004474315
0.0004474315
Average
Std Dev
3.26217137468983
3.26921877306635
3.23335606834288
3.25491540536635
0.019000531983015
Bleach (g)
mol Na2S2O3
mol OCl-
Mass % OCl-
0.9973
0.9982
0.9981
0.00056797934592 0.00028398967296 2.11974243007544
0.00056280245084 0.00028140122542 2.09852807255708
0.00055466733
0.000277333665
2.06840176561467
Average
2.09555742274906
Std Dev
0.025798924920038
Bleach (g)
mol Na2S2O3
1.0171
0.9924
0.999
0.00072032797256 0.00036016398628 2.6359853641415
0.00046296233144 0.00023148116572 1.73634199679532
0.00045260854128 0.00022630427064 1.68629528593009
Average
2.01954088228897
Std Dev
0.534442716969677
White Cloud
Trial
1
2
3
L
Thiosulfate
Used
0.00768
0.00761
0.0075
Great Value
Trial
1
2
3
L
Thiosulfate
Used
0.00974
0.00626
0.00612
mol OCl-
Mass % OCl-
Bleach (Sunlight Exposure) Titrations:
Standardization 3:
Mass KIO3: 1.0839g
Mol KIO3: 1.0839g
Trial
1
2
3
L Thiosulfate Added
0.0435
0.0431
0.04283
Average
Std Dev
M Thiosulfate
0.069861097974244
0.070509460832474
0.070953951946757
0.070441503584492
0.000549587201428
Great Value
Trial
L
Thiosulfate
used
0.02701
0.0255
0.02511
1
2
3
mol Thiosulfate
mol Hypochlorite
mass
bleach
0.001902625011817 0.000951312505909 1.038
0.001796258341405 0.000898129170702 0.9931
0.001768786155007 0.000884393077503 0.9913
Average
Std Dev
Mass %
(hypochlorite in
bleach)
6.82232205586062
6.73212521066126
6.64120051340111
6.73188259330766
0.090561014973982
White Cloud
Trial
1
2
3
L
Thiosulfate
Used
0.02771
0.02789
0.02756
mol Thiosulfate
mol Hypochlorite
Bleach
(g)
0.00204931089524
0.00206262291116
0.00203821754864
0.00102465544762
0.00103131145558
0.00101910877432
0.996
1.0013
1.0026
Average
Std Dev
L
Thiosulfate
used
0.02822
0.02819
0.02802
mol Thiosulfate
mol Hypochlorite
mass
bleach
Mass %
(hypochlorite in
bleach)
7.65816782337679
7.66711522554431
7.56657262720734
7.63061855870948
0.055645529990172
Clorox
trial
1
2
3
0.001987859231154 0.000993929615577 1.0262
0.001985745986047 0.000992872993023 1.0227
0.001973770930437 0.000986885465219 1.0335
Average
Std Dev
Mass %
(hypochlorite in
bleach)
7.20991235466431
7.22689602040312
7.10824905959189
7.18168581155311
0.064162517324569
Calculations:
Molarity of KIO3:
= 𝑔 𝐾𝐼𝑂3 ×
𝑚𝑜𝑙
1
×
𝑔
0.500 𝐿
Moles of KIO3:
= 𝑀𝑜𝑙𝑎𝑟𝑖𝑡𝑦𝐾𝐼𝑂3 × 𝑉𝑜𝑙𝑢𝑚𝑒𝐾𝐼𝑂3
Molarity of Thiosulfate:
𝑀𝑁𝑎2 𝑆2 𝑂3 = 𝑚𝑜𝑙𝑒𝑠𝐾𝐼𝑂3 ×
3 𝑚𝑜𝑙 𝐼3
2 𝑚𝑜𝑙 𝑁𝑎2 𝑆2 𝑂3
1
×
×
1 𝑚𝑜𝑙 𝐾𝐼𝑂3
1 𝑚𝑜𝑙 𝐼3
𝑉𝑜𝑙𝑢𝑚𝑒 𝑁𝑎2 𝑆2 𝑂3
Mol Thiosulfate Used:
𝑚𝑜𝑙𝑁𝑎2 𝑆2 𝑂3 = 𝑀𝑁𝑎2 𝑆2 𝑂3 × 𝑚𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠𝑁𝑎2 𝑆2 𝑂3
Mol Hypochlorite:
𝑚𝑜𝑙 𝑂𝐶𝑙 − = 𝑚𝑜𝑙𝑁𝑎2 𝑆2 𝑂3 ×
1𝑚𝑜𝑙𝑂𝐶𝑙−
2𝑚𝑜𝑙𝑁𝑎2 𝑆2 𝑂3
Mass % Hypochlorite in Bleach
−
𝑚𝑎𝑠𝑠% 𝑂𝐶𝑙 =
𝑚𝑜𝑙𝑂𝐶𝑙− × 74.44
𝑚𝑎𝑠𝑠 𝑏𝑙𝑒𝑎𝑐ℎ
𝑔
𝑚𝑜𝑙 × 100
Discussion:
Although we were able to collect plenty of usable data, there were many errors during the
course of the experiment. The samples that were exposed to sunlight did not have a steady and
constant source of UV rays, they were at the mercy of the weather. Some days were rainy so the
samples didn’t receive any sunlight, and some days were cloudy so they only received sunlight for part
of the day. In order to avoid this we should have placed them under UV lamps rather than just placing
them in a windowsill to get sunlight. The temperature of the light exposed sample was also constantly
changing due to weather or time of day. This fluctuation in temperature should have been documented.
The samples exposed to heat were also inevitably exposed to light due to the fact they were being
heated in clear beakers. Since the heating has a much more drastic effect on degradation than light
exposure, the slight light exposure may not have been significant. However, in an effort to avoid all
other variables in the experiment, we should have used a non-clear container to heat the samples in.
Conclusion:
In conclusion I am happy to say that this experiment was an amazing success. We were able to
record very precise data, not one of our standard deviations was above 1. Based on our results we see
that while all the bleaches degraded almost the same amount due to heat exposure, Clorox seems to be
affected much more by light exposure than the other brands. We also found that prolonged exposure to
heat above the recommended storage temp of 70°F has a much more significant effect on the
degradation of hypochlorite than prolonged light exposure. From our initial hypochlorite readings we
observed that Clorox actually had a higher weight percent than the advertised amount. With this data
we can make the assumption that Clorox adds more hypochlorite into their bleach initially as an attempt
to anticipate the degradation effect that happens while sitting on the shelf in a store, and to try to keep
a weight percent of around 8.25% longer than its competitors.