2.16     Heptane and octane form an ideal solution. At , the vapour pressures of the two liquid components are and   respectively. What will be the vapour pressure of a mixture of  of heptane and   of octane?

Vapour pressure of heptane =

and vapour pressure of octane =

Firstly we will find moles of heptane and octane so that we can find vapour pressure of each.

Molar mass of heptane =  7(12) + 16(1)  =  100 unit.

and molar mass of octane =  8(12) + 18(1) = 114 unit.

So moles of heptane :

and moles of octane :

Mole fraction of heptane =  0.456 and mole fraction of octane = 0.544

Now we will find the partial vapour pressure:-

(i) of heptane :-

(ii) of octane  :-

So total pressure of solution =

=  47.97 + 25.46 =   73.43 KPa

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