Question

A stock solution is made by dissolving 66.05 g of (NH4)2SO4 in enough water to make 250 mL of solution. A 10.0 mL sample of this solution is then diluted to 50.0 mL. Given that the molar mass of (NH4)2SO4 is 132.1 g/mol, what is the concentration of the new solution?
Use M subscript i V subscript i equals M subscript f V subscript f. and Molarity equals StartFraction moles of solute over liters of solution EndFraction..
0.400 M
1.60 M
5.00 M
10.0 M

Answer 1

First find moles in the stock: moles = 66.05 g / 132.1 g·mol⁻¹ = 0.500 mol.
Stock molarity = 0.500 mol / 0.250 L = 2.00 M.

Use dilution: Mf = Mi Vi / Vf = (2.00 M)(10.0 mL)/(50.0 mL) = 0.400 M.

Answer: 0.400 M.