6.90M solution of KOH in water contains 30% by mass of KOH. Calculate the density of the KOH solution. (Molar mass of KOH = 56 g `mol^(-1))`

Explanation

Mass of KOH = 30 g
`M = (n_(B))/(V(ml)) xx 1000`
`= (W_(B))/(M_(B) xx V(ml)) xx 1000 = (30)/(56 xx V) xx 1000`
`6.90 = (30 xx 1000)/(56 xx V)`
`V = (30 xx 1000)/(56 xx 6.90) = 81.43` mL
`D = (M)/(V)`
` = (100)/(81.43) = 1.28 g mL^(-1)`