Question

If 4 g of NaOH dissovles in 36g of `H_(2)O`, calculate the mole fraction of each component in the solution. (specific gravity of solution is `1g mL^(-1)`).
A. 2.5M
B. 3M
C. 2M
D. 1.5M

Answer 1

Correct Answer - A
Mass of `NaOH = 4g`
Number of moles of `NaOH = (4g)/(40g) = 0.1 mol`
Mass of `H_(2)O = 36g`
Number of moles of `H_(2)O = (36g)/(18g) = 2 mol`
Mass of solution = mass of water `+` mass of `NaOH = 36g + 4g = 40g`
Volume of solution` = 40 xx 1 = 40 mL`
(Since specific gravity of solution is `1g mL^(-1))`
Molarity of solution `=("Number of moles of solute")/("Volume of solution in litre")`
`= (0.1 mol NaOH)/(0.04L) = 2.5M`