A solution contains an unknown amount of dissolved magnesium. Addition of 5.34×10−2mol of Na2CO3 causes complete precipitation of all of the magnesium. What mass of magnesium was dissolved in the solution.

Answer 1

Mg^2+ + Na2CO3 ==> MgCO3 + 2Na^+

Convert mols Na2CO3 to mols Mg^2+ using the coefficients in the balanced equation.
mol Na2CO3 x (1 mol Na2CO3/1 mol Mg^2+) = mols Na2CO3 x 1/1 = ?
Then grams Mg = mols Mg x atomic mass Mg.