Question

How many grams of MgCO3 dissolved per litre gives 84 ppm hardness?

Group of answer choices

70.56 mg/L

48.23 mg/L

81.49mg/L

66.12 mg/L​

Answer 1

we have to find the grams of MgCO3 dissolved per litre gives 84 pm hardness.

solution : molar mass of MgCO3 = 24g + 12g + 3 × 16 = 84g

equivalent weight of MgCO3 = molar mass/n - factor

= 84/2 = 42g

similarly, molar mass of CaCO3 = 100g

so equivalent weight of CaCO3 = 100/2 = 50g

now considering 84 ppm of hardness mentioned in the term of equivalents of CaCO3.

hardness = mass of MgCO3 × equivalent weight of CaCO3/equivalent weight of MgCO3

⇒84 ppm = 84 gm/L = x × 50g/42g

⇒x = 84 × 42/50 = 70.56 g/L

Therefore the correct option is (a) 70.56 g/L.