The density of 2 M aqueous solution of NaOH is 1.28 ~g / cm ^3 . The molality of the solution is [Given that molecular mass of . NaOH =40 ~g ~mol ⁻¹ ]

Step-by-step solution

Given, molarity =2 M [i.e 2 mole NaOH in 1 ~L solution] Density ( d )=1.28 ~cm ⁻³ Molecular weight of NaOH =40 gmol ⁻¹ We know that, aligned & Density = mass of solution volume of solution & Mass of solution =1.28 ~g ~cm ⁻³ 1000 ~mL =1280 ~g & Moreover, molarity & = number of moles of solute volume of solution ( in mL ) 1000 & 2= mass of solute 40 1000 1000=80 ~g & Now, mass of solution = mass of solvent + mass of & solute & 1280 ~g = mass of solvent +80 & Mass of solvent =1280-80=1200 ~g =1.2 ~kg & Now, molality =