Home NCERT Solutions NCERT Exemplar CBSE Sample Papers NCERT Books Class 12 Class 10
Question 18

Calculate the mass of a non-volatile solute (molar mass 40 g mol-1) which should be dissolved in 114 g octane to reduce its vapour pressure to 80%.

Answer

Let the vapour pressure of pure octane be p10.

Then, the vapour pressure of the octane after dissolving the non-volatile solute is 80/100 p10 = 0.8 p10.

Molar mass of solute, M2 = 40 g mol - 1

Mass of octane, w1 = 114 g

Molar mass of octane, (C8H18), M1 = 8 × 12 + 18 × 1 = 114 g mol - 1

Applying the relation,

(p10 - p1) / p10    (w2 x M1 ) / (Mw1 )

(p10 - 0.8 p10) / p10    (w2 x 114 ) / (40  x 114 )

⇒ 0.2 p10 / p10   w2 / 40

⇒ 0.2 = w2 / 40

w2 = 8 g

Hence, the required mass of the solute is 8 g.

Popular Questions of Class 12th chemistry

Recently Viewed Questions of Class 12th chemistry

10 Comment(s) on this Question

Write a Comment: