Question

2. A simple distillation apparatus has a round bottom flask with a volume of 100 mL and a distillation head with a vertical volume of 12.0 mL. At the end of a distillation, vapor would fill this volume but could not be moved to the condenser. If no liquid remains, use the ideal gas law and a b.p. of 100°C at 760 mm Hg to calculate the volume of liquid in mL (d = 0.900 g/mL and m.w. = 200.0 g/mole) that condenses into the round bottom flask upon cooling.

3. Briefly define azeotrope. If you have a 50:50 mixture of ethanol and water, is it possible to obtain pure ethanol through fractional distillation?

Answer 1

2. From the Question, it is imperative that ,

At the end of distillation , vapour would fill all the volume (100+ 12= 102 mL)

So, we use ideal gas law to calculate the volume of liquid in mL that condenses into the round bottom flask upon cooling.

PV=nRT

=> V= nRT/P

now, n (mole)= Weight of liquid/ molar mass of liquid compound

= (d * V) /molar mass = (0.9 g. mL^-1* 112 mL ) / 200 g. mol^-1 = 0.504 mole

So, V= nRT/P

=( 0.504 mole * 8.314 * 10^-2 L . bar . K^-1 . mol^-1 * 373 K ) /  1.01 bar

= 15.4749 L = 15474.9 mL

3.  An azeotrope also termed as constant boiling point mixture . It means an azeotrope consists of the mixtures of two or more liquids whose distributions can't be changed by simple distillation procedure . Whenever an azeotrope is subjected to boiling condition , the vapour of azeotrope has the same ratio of constituents as the unboiled one. The composition of azeotrope is constant throghout distillation,

If we have a 50:50 mixture of ethanol and water, it is not possible to obtain pure ethanol through fractional distillation. Bacause ethanol and water, form azeotrope , where boiling point of ethanol is at 78⁰ C and boiling point of water is at 100⁰ C . So, azeotrope mixture boiling point is between 78⁰ C to 100⁰C . So its difficult to completly separate water from ethanol ,in  50:50 mixture of ethanol and water .Water should be boiled at its boiling point of 100⁰ C in order to remove it completly from  50:50 mixture of ethanol and water , but unfortunately its not the case with  50:50 mixture of ethanol and water azeotropic mixture.