Question

How many grams of magnesium chloride are needed to make 700ml of a 1.4 m solution?

Answer 1

Molarity is defined as the number of moles of solute in 1 L solution
molarity of MgCl₂ solution to be prepared - 1.4 M
volume of the solution to be prepared - 700 mL
the number of moles of MgCl₂ in 1 L - 1.4 M
therefore 700 mL should contain - 1.4 mol/L x 0.700 L = 0.98 mol 
molar mass of MgCl₂ - 95.2 g/mol 
mass of MgCl₂ required - 0.98 mol x 95.2 g/mol = 93.3 g
mass of MgCl₂ required is 93.3 g