Calculate the volume of 12 M Na2SO3 which needs to be added to 500.0 mL of water in order to produce a solution in which [Na+]= 0.200 M.

Use M1V1 = M2V2

12 mols/ L X 1 L/1000 mL X V1 =
0.2 mols/L X 1 L/1000 mL X 500 mL

Figure out V1 (in mL) .