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*Chemistry: Experiments > Q3. *Determine the concentration of free chlorine in swimming pool water > Flashcards

Q3. *Determine the concentration of free chlorine in swimming pool water Flashcards

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1
Q

List the chemicals required.

4

A

Deionised water

Calcium hypochlorite

Dilute solution of bleach

DPD number 1 tablet

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2
Q

What is the first step in this experiment?

A

Dissolve 0.01g calcium hypochlorite in deionised water and make the solution up to 1L to give a stock solution of 5 p.p.m

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3
Q

How much calcium hypochlorite is used to make the 5 p.p,m stock?

A

0.01g of calcium hypochlorite

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4
Q

0.01g calcium hypochlorite and 1L deionised gives a stock solution of what?

A

A stock solution of 5 p.p.m

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5
Q

What is the second step of the experiment, you have just made the 5 p.p.m stock?

A

Create a series of standard solutions; 5 p.p.m, 4 p.p.m, 3 p.p.m, 2 p.p.m and 1 p.p.m

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6
Q

How do you make a 5 p.p.m free chlorine solution?

A

Add 10 cm cubed of the stock solution to 0cm cubed of deionised water

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7
Q

How do you make the 4 p.p.m free chlorine solution?

A

Add 8 cm cubed of the stock solution to 2 cm cubed deionised water

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8
Q

How do you make the 3 p.p.m free chlorine solution?

A

Add 6 cm cubed of the stock to 4 cm cubed deionised water

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9
Q

How do you make the 2 p.p.m free chlorine solution?

A

Add 4 cm cubed of the stock to 6 cm cubed deionised water

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10
Q

How do you make the 1 p.p.m free chlorine solution?

A

Add 2 cm cubed of the stock to 8cm cubed deionised water

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11
Q

What is the third step of the experiment, you have made up all of your samples.
(2)

A

Add a DPD number 1 tablet to each of the solutions and allow time for the tablet to dissolve

If free chlorine is present, a pink colour will be observed in each solution

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12
Q

What should be added to each solution?

A

A DPD number 1 tablet

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13
Q

What colour can be seen when the DPD tablets are added?

A

A pink colour

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14
Q

What is the fourth step of the experiment, the solutions have turned pink?
(4)

A

Fill five cuvettes to about 75% capacity with each of the samples

Label each cuvette with the concentration of free chlorine in it

If air bubbles are observed in the solution, gentle tap the side of the cuvette to dislodge the bubbles

Using a piece of tissue paper, wipe the sides of the cuvette clean

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15
Q

What are the solutions transferred to?

A

Cuvettes

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16
Q

What are cuvettes?

A

The containers that fit into the colorimeter

17
Q

How much of the solution should be added to a cuvette?

A

75% capacity

18
Q

What should you label each cuvette with?

A

The concentration of free chlorine in the sample

19
Q

What should you do if there are air bubbles in the solution in the cuvette?

A

Gently tap the side of the cuvette to dislodge the bubbles

20
Q

What is the fifth step of the experiment, the cuvettes have been filled?
(3)

A

Calibrate the colorimeter using a cuvette containing deionised water

Make sure that the clear faces are lined up with the light path

Close the lid of the colorimeter

21
Q

How should you calibrate the colorimeter?

A

Place a cuvette containing deionised water into the cuvette holder in the colorimeter

22
Q

What should you make sure to do when placing the cuvette in the colorimeter?

A

Make sure that the clear faces are lined up with the light path

23
Q

What is the sixth step of the experiment, the deionised water is in the colorimeter?
(3)

A

Press the power switch and select the colour of light using RGB

Select absorbance by pressing A/T

Press CAL and wait until the unit reads zero absorbance

24
Q

How do you select the colour of light?

A

Using RGB

25
Q

How do you select absorbance?

A

By pressing A/T

26
Q

What button should you press to get the colorimeter to read zero?

A

CAL

27
Q

What is the seventh step of the experiment, the colorimeter reads zero?

A

Take a reading for each concentration of free chlorine

Record you results

Plot a graph of absorbance (on the y-axis) against concentration )on the x-axis)

28
Q

What should be on the y-axis of your graph?

A

Absorbance

29
Q

What should be on the x-axis of your graph?

A

Concentration

30
Q

What is the eight step of the experiment, the graph of absorbance (on the y-axis) against concentration )on the x-axis) has been drawn?
(2)

A

Insert a sample of the swimming-pool water/bleach into the colorimeter

Using the graph drawn, read off the corresponding concentration from the graph

*Chemistry: Experiments (15 decks)

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