Question

47. The density of 20% (w/w) aqueous NaOH
solution is 1.20 g.mL-! What is the mole
fraction of water ?(molar mass of NaOH
40g.mol-')
1) 0.95 2) 0.90 3) 0.97 4) 0.94​

Answer 1

Answer:

Dora amp parlors so all all so all do all P all

Answer 2

20%(w/w) aqueous solution NaOH means 20g NaOH in 100g solution.

Weight of solvent (water) = 100g - 20g = 80g

Given density of aqueous solution of NaOH = 1.20 g/ml

Mole fraction of water => no. of moles of water/(no. of moles of NaOH + no. of moles of water)

no of moles = weight/molecular weight

weight of water = 80g

molecular weight of water = 18g

no. of moles of water = 80/18 = 40/9

no. of moles of NaOH = 20/40 = 1/2

Mole fraction of water = (40/9)/(40/9 + 1/2)

= (40/9)/(89/18)

= 80/89

= 0.8988(nearly).

Nearest option is 0.90

option (2) is correct