CVEG 5230 L
Hardness and Alkalinity Lab
Introduction
Total hardness = calcium hardness + magnesium hardness
Total hardness = carbonate hardness + noncarbonate hardness
Carbonate hardness = alkalinity
noncarbonate hardness = total – alkalinity (if alkalinity < total hardness)
(if alk > total hardness, carbonate hardness = total hardness, noncarbonate hardness = 0)
In this laboratory exercise, we will measure total hardness, calcium hardness, and alkalinity. From the results we will calculate
magnesium hardness and carbonate and noncarbonate hardness.
We will divide into 3 lab groups to analyze three samples:
 Spring water
 Tap water
 Mystery water
Suggested Procedure: feel free to modify
A. Total hardness
1) Add 25 mL of sample water to 25 mL of distilled water in beaker.
2) Add 2 mL of buffer solution.
3) Add a couple drops or a partial scoop of Eriochrome Black T or other indicator. EBT will turn the solution purple.
4) Titrate the solution with 0.01 M EDTA (ethylenediaminetetracetic acid) until color change. EBT turns from purple to blue.
5) Record the mL of EDTA titrant.
B. Calcium hardness
1) Add 25 mL of sample water to 25 mL of distilled water in beaker.
2) Add 3 mL of 1.0 N Sodium Hydroxide (NaOH, “caustic soda”) solution to sample.
3) Add a couple drops or a partial scoop of Murexide or other indicator. Murexide will turn the solution pink.
4) Titrate with EDTA until color change. Murexide changes from pink to purple. Record the mL of EDTA used.
C. Alkalinity
1) Phenolpthalein step needed?
2) Add 40 mL of sample to beaker.
3) Add Methyl Orange, phenolphthalein or other indicator to sample. MO will turn the sample yellow.
4) Titrate sample with 0.02 N sulfuric acid (H2SO4) until color change. For MO, the sample turns orange. Record the mL of
H2SO4 titrant used.
D. Calculations
1) total hardness as mg/L of CaCO3 = A*B/(L of sample)
A = mL of EDTA titrant from step A.
B = mg of CaCO3 per mL of EDTA (convert 0.01 M EDTA to mg/mL as CaCO 3) (EDTA has 2 eq/mole)
= MEDTA*(EDTA eq per mole)*(eq wt of CaCO3)
= NEDTA*(eq wt of CaCO3)
note: that’s L of sample (=mL/1000)
2) calcium hardness as mg/L of CaCO3 = A*B/(L of sample)
A and B like total hardness calculation but use data from step B calcium hardness.
3) alkalinity = A*N*B/(L of sample)
A = mL of acid titrant used in step C alkalinity.
N = normality of acid used
B = eq wt of CaCO3 = (mol wt of CaCO3)/(eq/mole) = mg/eq
note: this is really just like the hardness calculations
4) from the results, calculate
magnesium hardness
carbonate and noncarbonate hardness
E. Report: total, calcium, magnesium, carbonate, and noncarbonate hardness. Alkalinity. Draw a bar-graph.
F.
Make up appropriate standards to check methods.