Question

If 15.0g of (NH4)2SO4 is dissolved in enough water to form 200mL of solution, what is the molarity of the solution?

Answer 1

Molarity is defined as the moles of solute per Liter solution.
So you'll have to convert 15.0 g (NH4)2 SO4 into moles, and 200 mL solution into Liters.
Then take the quotient:
\( \rm Molarity = \dfrac{moles}{Liter} \)

Answer 2

Converting from grams to moles means we have to find the molar mass. Just add the molar mass of each element, taking care not to skip the parentheses on (NH4)2. Then:
grams divided by (grams per mole) = moles