How many grams of MgCO3 dissolved per litre gives 290.66 mg/L hardness? (A)A. 70.56 mg/L B. 48.23 mg/LC. 81.49 mg/L D. 66.12 mg/L

The hardness of water is typically measured in terms of the concentration of calcium carbonate (CaCO3). However, in this case, we are dealing with magnesium carbonate (MgCO3).

The molar mass of MgCO3 is approximately 84.31 g/mol, while the molar mass of CaCO3 is approximately 100.09 g/mol.

The hardness of water due to MgCO3 can be calculated using the formula:

Hardness (as CaCO3) = [Concentration of MgCO3 (mg/L) * Equivalent weight of CaCO3] / Equivalent weight of MgCO3

The equivalent weight of a compound is its molar mass divided by its valence. Both MgCO3 and CaCO3 are divalent, so their equivalent weights are the same as their molar masses.

So, the hardness due to MgCO3 is:

Hardness = [MgCO3 * 100.09 g/mol] / 84.31 g/mol

If we want the concentration of MgCO3 that results in a hardness of 290.66 mg/L, we can rearrange the formula to solve for MgCO3:

MgCO3 = (Hardness * 84.31 g/mol) / 100.09 g/mol

Substituting the given hardness:

MgCO3 = (290.66 mg/L * 84.31 g/mol) / 100.09 g/mol

MgCO3 = 243.66 mg/L

This value does not match any of the options given in the question (A. 70.56 mg/L, B. 48.23 mg/L, C. 81.49 mg/L, D. 66.12 mg/L). There may be a mistake in the question or the answer choices.