Question

An aqueous solution which is 20% (w/w) and 30% (w/v) in NaOH. What will be mass fraction of water
in 30 ml of such solution

Answer 1

Explanation:

Let x be the mass of solution.

Mass of NaOH=100x×20

Molar mass of NaOH=40g

∴ Number of moles= (20x/100)/40=200x

Now mass of solvent in the solution= x−20x/100=80x/100x

∴ Molality= (80x/100)x/200×1000=6.25M

30% w/v of NaOH corresponds to 30 gm of NaOH in 100 ml solution.

Amount of NaOH present in 1000 ml solution is 300 gm.

Molarity of NaOH=300/40×1000/1000=7.5 M.

Answer 2

Answer:

mass fraction of water = 0.8

Explanation:

20%(w/w) of NaOH :-   20 g NaOH in 100g solution

30%(w/v) of  NaOH :-  30gm in 100ml of Solution

W of NaOH in 30 mL solution  =  (30/100)*30 g = 9g

Vol. of solution for 20g NaOH = (100/30)*20 mL = 200/3 mL

now,

200/3 mL of solution = 100 g solution

=>30mL of solution  =  45 g solution

now, mass of water in 45g solution = (45-9)g  =  36g

Mass Fraction of Water = 36/45 = 0.8