STOICHIOMETRY: QUANTITATIVE INFORMATION ABOUT CHEMICAL REACTIONS

Question

What mass of oxalic acid,H₂C₂O₄ is required to prepare 300 mL of a solution that has a concentration of 0.15 M H₂C₂O₄ ?

Mass___g

Answer 1

Recall that the molarity (0.15M) is telling us how many moles of the substance (oxalic acid) is dissolved in 1 liter (1000mL) of solution.

Molarity = moles of solute per liter of solution

a) Since we are told how many moles in 1 liter (Molarity) then we can find moles in 300 mL (0.300L).

Now, use the # of moles to find the # of grams of the solute (oxalic acid).

Moles of oxalic acid in 300 mL = (0.300L soln)( 0.15 mol acid/1L solution) = 0.0450 mol.

b) Using the molar mass of oxalic acid as 90.0 g/mol

Mass of oxalic acid = (0.0450 mol) (90.0 g/mol) = 4.05 g

Note: I chose to break this problem up in steps which in my opinion makes it easier to recall concepts.