The density of `4%` (w/v) NaOH soluton is 31.02 g/ ml. What is the molality of the solution? 

Explanation

`4%`(w/v) NaOH solution contains 4g of NaOH is 100ml of the solution.
density of the solution `= 1.02 g//ml`
`therefore` wt of of the solute in 100 ml of the solution = 4g
wt of 100 ml of the solution `= 100xx1.02 = 102 g`
wt. of solvent = Wt of solution` - `Wt of solute
`=102-4=98g`.
`therefore` Molality `= =((W)/(G.M.W))_("Solute")xx(100)/("wt of solvent in grams")`
`=(4)/(40)xx(1000)/(98)=1.02m`