Estimate The Concentration Of Free Chlorine Flashcards Preview

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Flashcards in Estimate The Concentration Of Free Chlorine Deck (17):
1

Describe a test for the presence of chloride ion in water

Add silver nitrate and dilute nitric acid and white precipitate forms

2

A colorimetric experiment was used to estimate the concentration of free chlorine in the swimming pool water sample. What is the general principle of all colorimetric experiments

Colour absorbance is promotional to concentration

3

Describe how you would estimate the concentration of free chlorine in a sample of swimming pool water using either a comparator or colorimeter

Fill each compartment of comparator with fresh portions of water sample
Add reagent DPD-1 to the sample of water, pink colour develops as DPD-1 reacts with free chlorine in the water
Compare with chart using solutions previously calibrated using solutions of known concentration of chlorine.
Hence, by comparing the pink colour of the swimming pool water with the pink colours of known concentrations of chlorine, the concentration of chlorine is estimated in ppm

4

Give a use of free chlorine

Disinfectant

5

What is free chlorine

Chlorine that exists in water as hypochlorous acid and hypochlorite ion

6

Why are free chlorine levels in swimming pool water higher than those in tap water
Give a reason why the concentration of free chlorine in treated drinking water is usually between .2-.5ppm whereas in swimming pool water it is 1-5ppm

In swimming pools, more bacteria from swimmers and in tap water it is less contaminated through processes of water treatment

7

Identify a reagent used to get for the presence of free chlorine in swimming pool water

DPD-1

8

State and explain the colour change that develops if free chlorine is present

DPD-1 is oxidised by chlorine to pink product
Orange/yellow to pink

9

What do the letters DPD stand for

Diethyl-phenylenediamine

10

Why is it necessary to use DPD tablets in this experiment

It reacts with chlorine in the water to give a coloured solution [pink]. The intensity of the colour depends on the concentration of chlorine present. Hence it is possible to estimate the concentration of chlorine in the water

11

In a certain school, swimming pool water was not available. What alternative could be used for this experiment

A dilute solution of bleach could be used
[hypochlorite ion present in bleach]

12

In what units is the concentration of free chlorine normally measured

Parts per million, p.p.m

13

What is the main source of nitrogen compounds in swimming pool water

Sweat

14

Is free chlorine an acidic or basic substance, explain your answer

Free chlorine is an acidic substance since the hypochlorous dissociates to form H+ ions and OCl- ions. The H+ ions make the water acidic
HOCl -> H+ + OCl-

15

Why is HOCL, a chlorine compound, used in swimming pools?

It sterilises swimming pool water and kills micro organisms by oxidation

16

What problem might arise for swimmers in a pool with
i) too much free chlorine
ii) not enough free chlorine

i) unpleasant smell and eye irritation
ii) disease (micro-organisms)

17

Give the name or formula of a free chlorine species in swimming pool water

Hypochlorite
Hypochlorous acid