Question

What is the mole fraction of each component in a solution made from 16 g MgSO4 and 100mL of H2O at 25 C , with a density of water at 25 C is .997g/mL?

Answer 1

Given the mass of MgSO4 = 16 g

molecular mass of MgSO4 = 120.3 g/mol

Hence moles of MgSO4 = mass / molar mass = 16 g / 120.3 g/mol = 0.133 mol

Given the volume of water, V = 100 mL

density of water, d = 0.997 g/mL

Hence mass of water in the solution, m = dxV = 0.997 g/mL x 100 mL = 99.7 g

molecular mass of water = 18.0 g/mol

Hence moles of water = mass/ mlecular mass = 99.7 g / 18.0 g/mol = 5.539 mol

Total moles in the solution = moles of MgSO4 + moles of H2O = 0.133 mol + 5.539 mol = 5.672

Hence mole fraction of MgSO4 = (moles of MgSO4) / total moles = 0.133 / 5.672 = 0.0234 (answer)

mole fraction of water = (moles of water) / total moles = 5.54 / 5.673 = 0.9766 (answer)