Question

Calculate the molality of NaOH in the solution prepared by dissolving its 4g in enough water to form 250 ml of the solution? ?? (In this from where do we get 4/40 ??? I'm very confused ... plss help me ....)

Answer 1

4/40 is the number of moles given in definition of molality

and calculating answer need to be 0.4 molal

Answer 2

= no of moles of solute /volume of solution in litres
= Mass of NaOH / Molar mass of NaOH /0.250 L
= 4 g / 40g / 0.250 L
= 0.1 mol /0.250 L
= 0.4 mol L
= 0.4 M
hope so u understood it :)