To estimate the concentration of free chlorine in swimming pool water or bleach using: i) A comparator or ii) A colorimeter

0.0(0)
studied byStudied by 0 people
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/7

encourage image

There's no tags or description

Looks like no tags are added yet.

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

8 Terms

1
New cards

Theory

• Chlorine is added to swimming pools to kill bacteria

• It reacts with the water as follows:

Cl2 + H2O ← → HOCl (hypochlorous acid) + HCl

• The hypochlorous acid then dissociates as a weak acid

HOCl ← → H+ + OCl –

• The amount of free chlorine in a sample of swimming pool water can be determined by establishing a relationship between the concentration of free chlorine in a sample and the amount of light the sample will absorb

• This is done in an instrument known as a colorimeter

2
New cards

Procedure

➢ Six standard solutions of chlorine are made up of concentrations:

0 ppm (deionised water only), 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm

➢ A DPD tablet is added to each and shaken until it dissolves – each solution turns a pink colour of different intensity

Note: The 0 ppm (deionised water) will remain colourless

➢ Each solution is placed in a cuvette and placed in the colorimeter and an absorbance reading is taken

➢ A graph is plotted of absorbance Vs concentration of free chlorine for the six solutions

➢ A DPD tablet is added to the sample of swimming pool water being tested, it is placed in a cuvette and placed in the colorimeter and its absorbance reading is also taken

➢ The graph is used to determine the concentration of free chlorine in the sample of swimming pool water/bleach

<p>➢ <strong>Six standard solutions of chlorine</strong> are made up of concentrations:</p><p>0 ppm (deionised water only), 1 ppm, 2 ppm, 3 ppm, 4 ppm, 5 ppm</p><p>➢ A <strong>DPD tablet is added</strong> to each and shaken until it dissolves – <strong>each solution turns a pink colour of different intensity</strong></p><p>Note: The 0 ppm (deionised water) will remain colourless</p><p>➢ Each solution is placed in a cuvette and placed in the colorimeter and <strong>an absorbance reading is taken</strong></p><p>➢ A graph is plotted of <strong>absorbance Vs concentration of free chlorine</strong> for the six solutions</p><p>➢ A<strong> DPD tablet is added to the sample of swimming pool water</strong> being tested, it is placed in a cuvette and placed in the colorimeter and its <strong>absorbance reading is also taken</strong></p><p>➢ The <strong>graph is used to determine the concentration of free chlorine</strong> in the sample of swimming pool water/bleach</p>
3
New cards

Name two species in swimming pool water known as free chlorine

• Hypochlorous acid (HOCl)

• Hypochlorite ion (OCl–)

Free chlorine species - effective at killing bacteria

4
New cards

What is meant by free chlorine?

Free chlorine is chlorine present in water in the form of hypochlorous acid (HOCl) and as hypochlorite ions (OCl-)

5
New cards

Name a reagent suitable to test for free chlorine in a water sample

A DPD tablet

6
New cards

How does this reagent indicate the presence of free chlorine in a sample?

• The solution will turn pink

• The more free chlorine present, the more intense the pink colour

7
New cards

What is the relationship between absorbance and concentration of free chlorine?

• Absorbance of light is directly proportional to concentration of free chlorine

• A straight-line graph through the origin (0,0) is obtained for a directly proportional relationship

8
New cards

Give a reason why the concentration of free chlorine in treated drinking water is usually between 0.2-0.5 ppm whereas in swimming pool water it should be between 1-5 ppm

• Swimming pool water has more bacteria added by people swimming in it

• Therefore the concentration of chlorine must be greater in swimming pools than in drinking water