COLORIMETRIC EXPERIMENT TO ESTIMATE FREE CHLORINE IN SWIMMING POOL WATER (OR BLEACH) USING A COMPARATOR Flashcards
what do you use
a Hach test kit
explain how a hatch test kit works
This is a coloured disk with different shades of red on the disk. The intensity of the ‘redness’ on the disk will give an estimation of how much free chlorine is present in the water sample from the swimming pool as it has been calibrated to give various concentrations of chlorine in water samples.
what chemical is used
DPD
if chlorine is present DPD will
turn red
degree of redness
depends on the concentration of chlorine
what does a hatch test kit consist of?
Colour viewing tubes (small test tubes). The bottom of these tubes are ‘frosted’ glass.
A coloured disk
A comparator box
first step
Deionised water is placed into one of the viewing tubes to a level just below the ‘frosted’ part of the glass. This was stoppered.
function of the first viewing tube
This tube is used as a reference tube to see how much light can be absorbed by this depth of water.
where is the reference tube placed?
The reference tube was placed into the comparator box to the left.
second tube
The same volume of swimming pool water was placed into another viewing tube and one of the sachets of chlorine free DPD was added to this. The tube was then stoppered and shaken to mix.
what can you note
Note the red colour of the water sample now.
where is the tube then placed?
This tube was then placed into the other opening of the comparator box.
coloured disk
The coloured disk was placed into the comparator box and the door was closed.
how to view
The comparator box was then held up to a light source and the two ‘windows’ in the front of the box were looked through.
how to find free concentration
The disk was then rotated until the colours in the two ‘windows’ matched.
The number on the disk was then read. This number gives the estimated concentration of free chlorine in the water in p.p.m.
