Question

400 g solution having 20% (w/w) solute is cooled,
then 50 g solute precipitated. The %(w/w) of
solute in remaining solution is
(1) 8.57%
(2) 15%
(3) 12.25%
(4) 9.5%
​

Answer 1

Answer:

The %(w/w) of solute in remaining solution is 8.57 %.

Explanation:

Given data :

Mass of the solution = 400 g  

Mass concentration %(w/w) = 20%

Mass of solute precipitated = 50 g

To find: %(w/w) of solute in remaining solution  

We know,  

Mass % = [(mass of solute) / (mass of solution)] * 100  

⇒20 = [(mass of solute) / 400] * 100

⇒ mass of solute = 80 g ..... [this is the mass before precipitation of solute]

Now,  

The remaining mass of the solution  

= (Total mass of solution) – (Mass of solute precipitated)

= 400 – 50

= 350 g

And,

Mass of remaining solute  

= (mass of solute before precipitation) – (Mass of solute precipitated)

= 80 – 50

= 30 g

Hence, the %(w/w) of solute in remaining solution is given by  

= [(mass of remaining solute) / (mass of remaining solution)] * 100

= [30 / 350] * 100

= 8.57%