Estimating the concentration of bleach
Apparatus
Conical side-arm flask (250 cm3)
Bung, with single hole to fit 10 cm3
syringe nozzle
Plastic syringe, to deliver 10 cm3 (Note 1)
Chemicals
Deionised or distilled water (25
cm3)
Access to the following solutions:
A variety of household bleach
solutions (IRRITANT)
Plastic syringe, to deliver 5 cm3 (Note 2)
Delivery tube (see diagram)
Rubber tubing, short length
Water trough or washing-up bowl
Measuring cylinder (100 cm3)
Hydrogen peroxide, ‘20 volume’
solution (IRRITANT at this
concentration), 10 cm3 per bleach
solution
Refer to Health & Safety and
Technical notes section below
for additional information.
Measuring cylinder (25 cm3)
Beaker (100 cm3)
Clamp and stand, 2
Procedure
1. Use a plastic syringe to measure out 5 cm3 of the first bleach into the flask. If
a ‘thick’ bleach is used, add approximately 25 cm3 deionised water. Swirl to
ensure complete mixing.
2. Discuss the fact that this dilution does not change the amount of bleach put
into the flask, but does enable proper mixing to take place and ensure the
reaction has goes to completion.
3. Half fill the trough with water. Submerge the 100 cm 3 measuring cylinder and
fill it with water, invert under water and clamp it in position.
4. Attach the delivery tube to the side arm flask and arrange the rest of the
apparatus as shown in the diagram below.
5. Measure 10 cm3 hydrogen peroxide solution into a clean plastic syringe,
attach it to the bung and gently empty the contents into the flask. Leave the
syringe in place.
6. Carefully swirl the contents of the conical flask and collect the gas liberated.
7. Continue until no further reaction is seen. Measure and record the final
volume.
8. Carefully disconnect the delivery tube from the flask.
9. Discard the solution into the sink. Flush away with plenty of water. Rinse the
flask thoroughly. Ensure any splashes of bleach are washed off skin
immediately and swabbed off benches.
10. If time allows, repeat the experiment with the same bleach to obtain three
results and take an average.
11. Repeat the experiment with different bleaches
Health & Safety and Technical notes
Household bleach solutions (containing sodium chlorate(I) / sodium hypochlorite)
(unlikely to be CORROSIVE but may be IRRITANT) - see CLEAPSS Hazcard.
Commercial household bleaches usually contain about 5% sodium chlorate(I). Some
bleaches also contain detergents and thickening agents, which may cause excessive
frothing in this experiment. Note that nowadays some commercially available
bleaches do not contain any chlorine and are based on peroxy-compounds. They
should not be used here.
Hydrogen peroxide solution, H2O2(aq), (IRRITANT at concentration used) - see
CLEAPSS Hazcard and CLEAPSS Recipe Book. Splashes of bleach and hydrogen
peroxide should be washed off immediately with plenty of water.
1 Plastic syringes are used to measure and deliver a known volume of hydrogen
peroxide solution, and their nozzles should fit tightly into the hole in the flask bung.
2 Plastic syringes can be used to measure 5 cm3 of bleach solution, but volumetric
pipettes with safety fillers could be used instead.