How Do You Calculate the Solubility of Sodium Sulfite?

[yspams]

I have a large exam tomorrow in chemistry and know how to do most problems on my practice test except these two

If the solubility of sodium sulfite (Na2SO3) is 27(g/100g water) at 20 degrees celsius, what is the mass percent concentration of the saturated solution of Na2SO3 at 20 degrees celsius?

How many grams of Na2SO3 * 7H2O is soluble in 50g water at 20 degrees celsius?



the answer to the first question is 21 and the 2nd answer is 37 but for the life of me I can't figure out how they got these answers.

 

[Bohrok]

For the first one, mass percent of Na₂SO₃ = mass of Na₂SO₃ / total mass of solution. If you assume you have a saturated solution with 27 g Na₂SO₃, what's the total mass of the solution? Then you'll need this result for the next one.

The second one is a little tricky since you're working with the added water in Na₂SO₃·7H₂O. Use the equation for finding the mass percent of Na₂SO₃ while using x for the moles of Na₂SO₃ and Na₂SO₃·7H₂O; this mass percent of Na₂SO₃ must be equal to the mass percent you got for the first problem.