Learning Objectives At the end of this lesson you will be able to: Dilute “over-range” samples

1. Learning Objectives • At the end of this lesson you will be able to: • Dilute “over-range” samples 1

2. Diluting “over-range” samples If a sample turns yellow after adding the DPD powder or if the display flashes 2.20 then the water sample must be DILUTED. 2

3. Diluting “over-range” samples- using a measuring cylinder • A fresh sample is diluted with de-ionised water. • Pour 10 mL of sample into a measuring cylinder. 3

4. Fresh water sample diluted with de-ionised • water • Add 10 mL of de-ionised water and mix carefully without splashing by swirling. • The sample is ready for testing. 4

5. Measuring diluted samples Using the diluted sample, fill the cell exactly to the 10 mL mark. The sample is ready for testing. Note: Very important step when measuring diluted samples. 5

6. Measuring diluted samples Remember to multiply your results by 2 to get the correct concentration for the water sample. Why do we need to do this? Clickherefor answer. 6

7. Measuring diluted samples Remember to multiply your results by 2 to get the correct concentration for the water sample. Why do we need to do this? Because you halved the concentration of chlorine with the dilution. 6

8. 1 2 Add 10 mL of de-ionised water and mix Take 10 mL of the DILUTED water sample Diluting over range samples If the sample is still “over-range”, you may dilute it a second time as described. (This is called a double dilution – you should not dilute more than twice) 7

9. Diluting “over-range” samples Use the “twice” diluted sample for your analysis. Remember to multiply the result by 4 to get the correct chlorine concentration. Why do we need to do this? Clickherefor answer. 8

10. Diluting over range samples Use the “twice” diluted sample for your analysis. Remember to multiply your result by 4 to get the correct chlorine concentration. Why do we need to do this? The sample is 4 times weaker so the correct chlorine value will be 4 times greater than displayed result. 8

11. Diluting “over-range” samples using 2 cells • You will dilute the sample using the 10 mL mark on the cell. • Fill a cell to the 10 mL mark with sample. • Fill a second cell to the 10 mL mark with de-ionised water 9

12. Diluting “over-range” samples using 2 sample • cells • Add the de-ionised water to the sample cell, cap and mix carefully. • Adjust the level to the 10 mL mark by carefully tipping some of the diluted sample out. • The sample is ready for testing. 10

13. Quiz- Question 1 of 1 Which of the following statements is true? a) If the chlorine meter display flashes 2.20, the sample is too concentrated. b) When diluting the sample for the 1st time, for correct concentration, multiply result by 2. c) It’s vital to fill the cell to exactly 10 mL mark when measuring volumes of sample or deionised water. d) All of the above Clickherefor answer. 11

14. Quiz 1- Answer Which of the following statements is true? d) All of the above 11

15. Summary • This section covered: • Instructions for diluting “over-range” samples using: • measuring cylinders • 10 mL HACH cells 12