Estimate the concentration of free chlorine in swimmingpool water or bleach using a comparator

Step 1

Set up apparatus as shown with one test tube containing deionised water + one containing pool water with one dissolved DPD tablet

Step 2

Compare test sample to matching colour in comparator disc

What is free chlorine?

Cl that exists in water as hypochlorous acid or hypochlorite ions

What problem does too high free chlorine concentration in swimming pools cause?

Irritates swimmer’s eyes

Is free chlorine acidic or basic? Why?

Acidic as hypochlorous acid dissociates to form H+ and OCl- ions

Principle behind a comparator

Colour produced by water containing DPD is compared to comparator disc to indicate free Cl conc.

What does DPD stand for?

Diethyl phenylene diamene

What happens when a DPD tablet is added to water with free chlorine?

Water turns pink

Why are DPD tablets used in this experiment?

Produces more intense colour in water with higher conc. of chlorine

If swimming pool water isn’t available what could be used as a sample instead?

Dilute bleach

What units is the conc. of free chlorine measured in?

p.p.m

Main sources of nitrogen compounds in swimming pool water

Sweat. Urine

Draw a diagram of this experiment

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