Name Section QUESTIONS: EXPERIMENT 17 Date In a hardness of water determination

Question

Name Section QUESTIONS: EXPERIMENT 17 Date In a hardness of water determination like the one performed in this experiment, it was found that a 25.00-mL sample of water required 12.25 mL of 0.0128 M EDTA solution for complete titration. What is the concentration (molarity) of Ca ions in the water sample? What is the concentration of CaCO (in mg/L) in the water sample? Describe the hardness level of the water using the U.S. government standards Ca2 molarity CaCOs concentration, mg/L hardness leve 167

Explanation / Answer

Answer...

Hardness of water is due to the presence of bicarbonate, sulphate and chloride of Calcium and Magnesium. Generally we measure the hardness as concentration of Ca salt only. The sample of water is titrated against standard EDTA solution and hardness is calculated easily in the unit of milligrams per litres.

Ca2+ + EDTA4- => CaEDTA2-

CaCO3 + EDTA4- => CaEDTA2- + CO3 - -

If M and V terms denotes the molarity and volume of the titer and the titrant.

M1V1 = M2V2

25xM1 = 0.0128x12.25

=> M1 = 0.0128x12.25/25 = 0.006272 moles/L. Ans.

Now, gm molecular weight of CaCO3 = 100 gm(1 mole)

M solution of CaCO3 is the solution having 1 mole of it dissolved in one Liter of the solution.

(M) soln - - > 100gm/L = 100000 mg/L

Thus, concentration of CaCO3 in M/L 100000 mg/L

So, 0.006272 moles per Liter = 100000x0.00627

= 627.2mg/L. Ans.

The US Environment Protection Agency has not set any legal limit or standard of hardness of water. It is because the chemicals which are cause of hardness of water do not produce any health hazards. They are not poisons.

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