Question

(35 points) For the following water sample please complete the table (meq/L and mg/L as CaCO3) and the questions that follow (Remember - 50 mg CaCO3/meq CaCO3) lon mg/L mg/meq meq/L (Please fill in the values below) as CaCO3 mg/L HCO3 125 61.0 2- 35 250 30.0 Mg K* Fe2 Mn2+ SO.2 NO3 NO2 Ca2 12.2 100 39.1 27.9 175 12 27.5 300 48.0 62.0 2 0.1 46.0 155 125 20.0 CI Na* 35.5 25 23.0 pH 7.0 (15 points) What is the total hardness as mg/L as CaCO3? (15 points) What is the carbonate hardness as mg/L as CaCO3 not including pH? (5 points) Name five additional ions (not in the table above) that could contribute to total hardness

Answer 1

The formula for the conversion is

meq/L = (mg/L) / EW of the ion

And mg/L = meq/L x 50 g/eq [as the equivalent weight of CaCO3 is 50]

Eqivalent weight of the ions are:

HCO3- = 61,

CO₃^2-= 30,

Mg2+ =12.2  

K+ = 39.1,

Fe2+ =27.9 ,

Mn2+ = 27.5,

SO₄^2- = 48,

NO3- = 62,

NO2- = 46,

Ca+2 =20 ,

Cl- = 35.5,

Na+ = 23

Hence for HCO3-: meq/L = 125/61= 2.049

For CO₃^2- : meq/L = 35/30= 1.166; mg/L as CaCO3 = 1.166 x50 = 58.3

For Mg²⁺: meq/L = 250/12.2 = 20.49 ; mg/L as CaCO3 = 20.49 x50 = 1024.5

For Fe2+ : meq/L = 175/27.9= 6.27; mg/L as CaCO3 = 6.27 x50 = 313.5

For K+ :  meq/L = 100/39.1= 2.557; mg/L as CaCO3 = 2.557x50 = 127.85

For, Mn2+ : meq/L = 12/27.5= 0.436; mg/L as CaCO3 = 0.436 x50 = 21.8

For, SO₄^2- : meq/L = 300/48 = 6.25; mg/L as CaCO3 = 6.25 x50 = 312.5

For, NO3- : meq/L = 2/62= 0.032; mg/L as CaCO3 = 0.032x50 = 1.6

For, NO2- :  meq/L = 0.1/ 46 = 0.002, mg/L as CaCO3 = 0.002 x50 =0.1

For, Ca+2 : meq/L = 155 /20 = 7.75; mg/L as CaCO3 = 7.75 x50 = 387.5

For, Cl- : meq/L = 125 /35.5 = 3.52; mg/L as CaCO3 = 3.52 x50 = 176

For, Na+: meq/L = 25 /23 = 1.087; mg/L as CaCO3 = 1.087 x50 = 54.35

Total hardness as mg/L as CaCO3 = Ca hardness + Mg hardness

= 387.5 + 1024.5 = 1412 as CaCO3

The other five ions that can contribute to total hardness may be

OH-, OCl-, PO₄^3-, NH₄⁺, Al³⁺