Lago Enriquillo

Environmental Health 11

Lab#7 Removal of Water Hardness
By Precipitation with Soda Ash

Angel Nunez

Prof. Dickems

4/05/12

Objective:
To determine the optimum dose of soda ash thatwill remove calcium
hardness from water.

Experimental Procedure:
1. Determine the hardness of the original water sample according to the hardness test procedure.
2. Pour out 500mL of hardwater sample into each of 5 beakers.
3. To the first beaker O mL of Na2CO3 solution and mix rapidly for 1 minute (this corresponds to a NaVO3 dose of 0 mg/L). This is the control sample.
4.To the second beaker add 2.5 mL of NaCO3 solution and mix rapidly for 1 minute (this corresponds to a NaCO3 dose of 50 mg/L).
5. To the third beaker add 5 mL of Na2CO3 solution and mix rapidly for1 minute (this corresponds to a NaCO3 dose of 100 mg/L).
6. To the fourth beaker add 10 mL of Na2CO3 solution and mix rapidly for 1 minute (this corresponds to a NaCO3 dose of 200 mg/L).
7. Tothe fifth beaker add 20 mL of Na2CO3 solution and mix rapidly for 1 minute (this corresponds to a NaCO3 dose of 400 mg/L).
8. After 5 minutes have elapsed for each beaker, check the pH of thewater with the pH paper.
9. If the pH is less than 9 add drops of 1M NaOH and mix rapidly for about 10 seconds.
10. Check the pH after again.
11. Repeat steps 9-10 until the pH isapproximately 9.
12. Once the pH in each beaker is 9 allow the beaker to stand for 20 minutes.
13. Take a 50 mL sample from the top of each beaker and measure the hardness.
14. Record your results onthe data table.
15. Calculate the residual hardness of each sample.

Materials
1. Buret
2. 50 mL graduated cylinder
3. 50 mL beakers
4. Hardness buffer
5. 0.01M EDTA Titrant6. Eriochrome Black T Indicator
7. Hard Water Sample (Unknown Hardness Concentration)
8. 1000 mg/L Sodium Carbonate (Na2CO3) Solution.

Data Sheet
Dose of Na2CO3(Mg/L) | Volume of...