Question

Calculate the molarity of NaOH in the solution prepared by dissolving its 4 g in enough water to form 250 mL of the solution

NCERT Class XII
Chemistry - Main Course Book I

Chapter 1. Some Basic Conpepts of Chemistry

Answer 1

Molarity(M) = w × 1000 / GMW × V

where,
w = given weight of the solute = 4g
GMW = Gram Molecular Weight of the solute = 40g
V = Volume of the solution in ml. = 250 ml

So,
M of NaOH
= 4 × 1000 / 40 × 250
= 0.4 M

Answer 2

Molarity  (M) = No. of moles of solute/Volume of solution in litres  No. of moles= mass of NaOH / molar mass of NaOH                        = 4g / 40g                       = 0.1 molecular Volume = 250 / 1000Lit               = 0.250L M= 0.1 mol/ 0.250L    = 0.4M