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 (in 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

Given that the hardness is 290.66 mg/L, we can solve for the concentration of MgCO3:

290.66 mg/L = [MgCO3 * 100.09 g/mol] / 84.31 g/mol

Rearranging for MgCO3 gives:

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

Calculating this gives a concentration of MgCO3 of approximately 243.56 mg/L.

This value does not match any of the options provided (A. 70.56 mg/L, B. 48.23 mg/L, C. 81.49 mg/L, D. 66.12 mg/L), suggesting that there may be an error in the question or the provided options.