Question

An analysis of groundwater samples from Fresno, CA taken in 2013 is given below. Determine the calcium, magnesium, and iron hardness of the water expressed as meq/L and mg/L as CaCO3. Determine the total hardness and alkalinity as well. Also, determine the nitrate concentration in terms of mg/L as N.

Constituent	Concentration(mg/L)
Calcium	20.2
Magnesium	20.5
Sodium	20.3
Potassium	2.17
Bicarbonate	175
Sulfate	5.37
Chloride	9.1
Flouride	.12
Nitrate	2.73
Silica	43.4
pH	7.7 pH units

Answer 1

Calcium Hardness as CaCO3 = concentration of calcium x (molar mass of CaCO3/molar mass of Calcium)

molar mass of calcium = 40 g/mol

molar mass of CaCO3 = 100 g/mol

given concentration of calcium = 20.2 mg/L

Ca hardness = 20.2 x (100/40) mg/L = 50.5 mg/L

meq = mg / atomic weight x valence

for calcium, valence = 2

Ca hardness = 50.5 / 40 x 2 = 2.51 meq/L

Magnesium Hardness as CaCO3 = concentration of Mg x (molar mass of CaCO3/molar mass of Mg)

molar mass of Mg = 24.3 g/mol

given concentration of Mg = 20.5 mg/L

Mg hardness = 20.5 x (100/24.3) = 84.36 mg/L

for Magnesium, valence = 2

Mg hardness = 6.94 meq/L

concentration of nitrate in N = 0.00273/62 = 0.000044 N