5 (3.5) Distillation

Question 1

Preparation of cyclohexene? (Mark scheme answer)

Answer 1

1. Acidify the potassium manganate(VII) solution combining a volume of a regular laboratory concentration with an equal volume of dilute sulfuric acid.
2. Pour the mixture into a pear-shaped/round flask, with a still head containing a thermometer.
3. Attached to a condenser with a ice cooled collecting vessel.
4. Add a few anti-bumping granules.
5. Heat the flask gently.
6. Collect sample at boiling point of the desired product.
7. The cooled collection vessel is essential to reduce evaporation of the product.

Question 2

Why water bath?

Answer 2

should be used to heat the mixture if there are flammable substances present

Question 3

Anti bumping granules?

Answer 3

prevent large bubbles from forming and ensure that the liquid doesn’t boil too vigorously as this would result in
the mixture boiling over into the condenser and undesired impurities would contaminating the product.

Question 4

Condenser should be?

Answer 4

tilted slightly down, so any liquid can run into the collection flask.

Question 5

Bulb of thermometer should be?

Answer 5

at the T junction connecting to the condenser to measure the correct boiling point

Question 6

Water must?

Answer 6

enter at the lowest point and leave at the highest point to go against gravity as this ensures that water fills the
condenser (prevents backflow of water), maximising heat transfer for condensation (more efficient cooling).

Question 7

Why should Collection flask should not be sealed to condenser?

Answer 7

system should not be air tight because as it is heated the air inside the
system expands. If it is air tight then the air cannot escape and may cause the apparatus to crack.

Question 8

Separation after distillation?

Answer 8

-product after distillation still contain impurities
-transfer product mixture to separating funnel + add water to dissolve water soluble impurities + create aqueous solution
-drain aqueous lower layer, leaving impure cyclohexane

Question 9

Purification of cyclohexane

Answer 9

-drain cyclohexane into round bottomed flask
-add anhydrous CaCl2 (drying agent)and stopper flask. Let mixture dry for at least 20 mins, swirling occasionally
-distil again

Question 10

Distillation?

Answer 10

Liquid heated to create vapour- cooled + condensed by condenser + liquid drip back into flask
Species separate due to boiling points

Question 11

Draw diagram of apparatus set up

Answer 11

On photos

Question 12

How do you isolate a liquid product?

Answer 12

-You can use a separating funnel to isolate the organic layer from the aqueous layer
-shake the flask allow the layers to separate
-then open the tap and run off one layer into separate container

Question 13

How can you confirm you’ve made alkene ?

Answer 13

Test distillate using bromine water (orange—> colourless if present)

Question 14

Saturated sodium chloride solution + anhydrous calcium chloride?

Answer 14

Drying agents- remove water