Intro to Chem Question

Question

A solution contains an unknown amount of dissolved magnesium. Addition of 0.0877 mol of Na2CO3 causes complete precipitation of all the magnesium. What is the maximum mass of magnesium that was dissolved in the solution.

How would I approach this problem?

Answer 1

Looking at the reaction taking place:

Mg²⁺(aq) + Na₂CO₃(aq) ==> MgCO₃(s) + 2Na⁺(aq) ... balanced equation

Next, use the stoichiometry of the balanced equation to find the mols of MgCO₃ formed, since all of the Mg in the original sample ends up in MgCO₃ as a precipitate:

0.0877 mol Na₂CO₃ x 1 mol Mg / 1 mol Na₂CO₃ = 0.0877 mols Mg originally present.

Finally, convert mols Mg to grams Mg using the atomic number of 24.3 g/mol

0.0877 mols Mg x 1 mol / 24.3 g = 2.13 g Mg was dissolved