Q3. *Determine the concentration of free chlorine in swimming pool water Flashcards
List the chemicals required.
4
Deionised water
Calcium hypochlorite
Dilute solution of bleach
DPD number 1 tablet
What is the first step in this experiment?
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
How much calcium hypochlorite is used to make the 5 p.p,m stock?
0.01g of calcium hypochlorite
0.01g calcium hypochlorite and 1L deionised gives a stock solution of what?
A stock solution of 5 p.p.m
What is the second step of the experiment, you have just made the 5 p.p.m stock?
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
How do you make a 5 p.p.m free chlorine solution?
Add 10 cm cubed of the stock solution to 0cm cubed of deionised water
How do you make the 4 p.p.m free chlorine solution?
Add 8 cm cubed of the stock solution to 2 cm cubed deionised water
How do you make the 3 p.p.m free chlorine solution?
Add 6 cm cubed of the stock to 4 cm cubed deionised water
How do you make the 2 p.p.m free chlorine solution?
Add 4 cm cubed of the stock to 6 cm cubed deionised water
How do you make the 1 p.p.m free chlorine solution?
Add 2 cm cubed of the stock to 8cm cubed deionised water
What is the third step of the experiment, you have made up all of your samples.
(2)
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
What should be added to each solution?
A DPD number 1 tablet
What colour can be seen when the DPD tablets are added?
A pink colour
What is the fourth step of the experiment, the solutions have turned pink?
(4)
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
What are the solutions transferred to?
Cuvettes
What are cuvettes?
The containers that fit into the colorimeter
How much of the solution should be added to a cuvette?
75% capacity
What should you label each cuvette with?
The concentration of free chlorine in the sample
What should you do if there are air bubbles in the solution in the cuvette?
Gently tap the side of the cuvette to dislodge the bubbles
What is the fifth step of the experiment, the cuvettes have been filled?
(3)
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
How should you calibrate the colorimeter?
Place a cuvette containing deionised water into the cuvette holder in the colorimeter
What should you make sure to do when placing the cuvette in the colorimeter?
Make sure that the clear faces are lined up with the light path
What is the sixth step of the experiment, the deionised water is in the colorimeter?
(3)
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
How do you select the colour of light?
Using RGB
How do you select absorbance?
By pressing A/T
What button should you press to get the colorimeter to read zero?
CAL
What is the seventh step of the experiment, the colorimeter reads zero?
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)
What should be on the y-axis of your graph?
Absorbance
What should be on the x-axis of your graph?
Concentration
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)
Insert a sample of the swimming-pool water/bleach into the colorimeter
Using the graph drawn, read off the corresponding concentration from the graph
