Question

A solution is prepared by dissolving 20.1 g of MgCl2 with the addition of 157.0 mL of water (density of water is 1.00g/cm3). The density of the resulting solution was determined to be 1.089g/cm3. Calculate the molar concentration of this solution: Hint: Make sure you understand the definition on Molar concentration

Answer 1

1.3 M.

Step-by-step explanation:

• We need to calculate the mass of the solution:

mass of the solution = mass of MgCl₂ + mass of water

mass of MgCl₂ = 20.1 g.

mass of water = d.V = (157.0 mL)(1.0 g/cm³) = 157.0 g.

∴ mass of the solution = mass of MgCl₂ + mass of water = 20.1 g + 157.0 g = 177.1 g.

• Now, we can get the volume of the solution:

V of the solution = (mass of the solution)/(density of the solution) = (177.1 g)/(1.089 g/cm³) = 162.62 mL = 0.163 L.

Molarity is the no. of moles of solute dissolved in a 1.0 L of the solution.

M = (no. of moles of MgCl₂) / (Volume of the solution (L)).

∴ M = (mass/molar mass)of MgCl₂ / (Volume of the solution (L)) = (20.1 g/95.211 g/mol) / (0.163 L) = 1.29 M ≅ 1.3 M.