The Total solution for NCERT class 6-12
Heptane and octane form an idealsolution. At 373 K, the vapour pressures of the two liquid components are 105.2kPa and 46.8 kPa respectively. What will be the vapour pressure of a mixture of26.0 g of heptane and 35 g of octane?
Vapour pressure of heptane
We know that,
Molar mass of heptane (C7H16)= 7 × 12 + 16 × 1
= 100 g mol−1
Molar mass of octane (C8H18)= 8 × 12 + 18 × 1
= 114 g mol−1
= 0.31 mol
= 0.456
And, mole fraction ofoctane, x2 = 1 − 0.456
= 0.544
= 0.456 × 105.2
= 47.97 kPa
= 0.544 × 46.8
= 25.46 kPa
Hence, vapour pressure ofsolution, ptotal = p1 + p2
= 47.97 + 25.46
= 73.43 kPa