Question

A 30 mL sample which appeared to be a clear, colorless liquid was distilled by simple distillation (using a heating mantle and variac as the heat source). When the first drop of liquid

was observed the temperature was 77°C and the temperature remained in the range of 77°C to 80°C while the collection rate remained fairly constant for the remainder of the distillation.

After approximately 15 mL of distillate had distilled, the liquid stopped boiling, even though the heating was continued. After the heating was discontinued, approximately 15 mL of clear,

colorless liquid remained in the initial flask. Can this initial 30 mL sample be considered to be a

fairly pure liquid? Explain.

Answer 1

Solution :-

The total volume of the solution=30.0 mL

The volume of the solution distilled out = 15.0 mL

Volume remained undistilled = 15.0 mL

The temperature of the solution at the boiling point (distillation temperature range = 77- 80 C)

The solution started to boil and distilled out at 77 degree Celsius means one of the components of the mixture is having lower boiling point, therefore, it starts to boil at 77 degree Celsius and evaporated and gets separated from the other component which is having higher boiling point than 80 degree Celsius therefore even after the heating is continued for some time it does not reach to its boiling point and therefore remain undistilled.

Therefore we can say that the original 30 ml solution was not pure liquid but rather it is a mixture of two liquids in which one liquid is having a lower boiling point and the other is having a higher boiling point.

So the original 30 mL solution is not pure liquid.