Question

A 6.90 M solution of KOH in water contains 30% by mass of KOH .What is the density of solution

Answer 1

Dear student,


6.90 M solution of KOH means 6.90 mol of KOH in 1 L solution.
1L = 1000 cm³

So, 6.90 mol of KOH is present in 1000 cm³ of solution.

Mass of 6.90 mol of KOH = 6.90 $\times$56 g mol^-1 (Molar mass of KOH)
= 386.4 g


30% solution of KOH means 30 g KOH is presnt in 100 g of solution
1 g of KOH is present in (100/ 30) g of solution
384.4 g of KOH will be present in (100 x 386.4 ) / 30 = 1288 g of solution

Density of KOH solution = (Mass / Volume ) = ( 1288/1000) = 1.288 g cm^-3

Thus, the density of the solution = 1.288 g cm^-3

Regards