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The free chlorine present in swimming-pool water can be measured using a colorimeter or comparator - Leaving Cert Chemistry - Question c - 2003
Question c
The free chlorine present in swimming-pool water can be measured using a colorimeter or comparator. (i) What is the principle on which the technique that uses each ... show full transcript
Worked Solution & Example Answer:The free chlorine present in swimming-pool water can be measured using a colorimeter or comparator - Leaving Cert Chemistry - Question c - 2003
Step 1
What is the principle on which the technique that uses each of these methods is based?
Answer
The measurement of free chlorine using a colorimeter or comparator is based on the principle of absorbance or intensity of color that is formed when chlorine reacts with a suitable reagent. Specifically, the absorbance of light at a particular wavelength is measured, which correlates directly to the concentration of chlorine in the sample.
According to Beer-Lambert Law, the absorbance ( A ) is proportional to the concentration ( C ) of the substance in solution, thus: where A is the absorbance, C is the concentration of the absorbing species, l is the path length through which the light travels, and k is a proportionality constant. Therefore, the greater the concentration of free chlorine, the deeper the color and higher the absorbance measured.
Step 2
What is meant by free chlorine?
Answer
Free chlorine refers to the total amount of chlorine that is available in swimming pool water for disinfection. It exists primarily in two forms:
- Chlorine gas (Cl₂): which is a potent oxidizing agent.
- Hypochlorous acid (HOCl) and hypochlorite ions (OCl⁻), which are formed when chlorine dissolves in water.
Free chlorine is effective in killing bacteria, viruses, and other pathogens present in water, providing a safe swimming environment.