If 4 g of NaOH dissolves in 36 g of H2O, calculate the mole fraction of each component in the solution. Also, determine the molarity of solution (specific gravity of solution is 1g mL–1).
There are two components in the NaOH solution, NaOH and H2O. The mole fraction of a component is given by the formula
Number of moles of H2O = Mass/Molar mass = 36/18 = 2 moles
Number of moles of NaOH = 4/40 = 0.1 moles.
Total number of moles = 2 + 0.1 = 2.1 moles.
Mole fraction of H2O = 2/2.1 = 0.952
Mole fraction of NaOH = 0.1/2.1 = 0.048
Specific gravity is the density of a substance divided by density of water. Here, the density is 1g mL-1. Mass of the solution is the sum of mass of NaOH and mass of H2O = 4 + 36 = 40g.
Volume of solution = Mass/density
Volume of solution = 40mL.
Molarity = 0.1 moles/0.04L = 2.5M.