Edexcel A-Level Chemistry AS 10.19 Understand the Following Techniques in the Preparation and Purification of a Liquid Organic Compound I Heating Under Questions

An answer that makes reference to the following:

- (anti-bumping granules) provides a nucleus on which gas bubbles grow

Accept provide a surface /site for bubbles to form on Allow prevent local heating / superheating

Allow 'distribute the heat'

Allow prevent the (sudden) production of large gas bubbles (which cause bumping)

Allow ensures that gas bubbles are small

Ignore stir the reaction mixture

Ignore prevent flash boiling / sudden boiling

(1)

An answer that makes reference to the following points:

- (fractional distillation) gives better separation of the substances in the reaction flask (than simple distillation)

- (fractional distillation column) gives longer reaction

(1) time

OR

- 'better separation of cyclohexene and water' scores 2 marks

Allow (fractional distillation) is more effective / efficient (than simple distillation)

Allow just 'better separation' is achieved Allow purer product obtained Ignore reference to increased yield Ignore 'more accurate' Ignore 'similar boiling temperatures'

Accept fractional distillation column acts like a reflux condenser

Accept cyclohexanol has a higher boiling temperature (than cyclohexene) so is returned to the flask, increasing reaction time / yield

Allow to give (more) complete reaction

Just ' separation of cyclohexene and water' scores (1)

(2)

A diagram that shows the following:

- separating funnel

- top layer labelled cyclohexene / organic and lower layer labelled water / aqueous

(1)

The funnel must have a tap and have a neck capable of being closed with a stopper or a bung Allow round separating funnel Allow bung / stopper not shown Ignore tap at the top

Do not award a filter funnel Do not award funnel without some sort of tapering at the neck

Allow for (2)

Allow minor error in organic name e.g. cyclohexane Ignore ‘inorganic lower layer’ Do not award if cyclohexanol is in the lower layer

(2)

An explanation that makes reference to the following points:

- (the organic layer) changes from cloudy to clear

- (anhydrous calcium chloride) removes the (traces of) water

(1)

Allow just 'becomes clear / transparent' Ignore 'less cloudy', clearer, more transparent Ignore white Ignore colourless Ignore the drying agent clumps together Ignore layers disappear

Accept (anhydrous calcium chloride) dries the cyclohexene Allow (anhydrous) calcium chloride is a drying agent Ignore calcium chloride becomes hydrated

(2)

An answer that makes reference to the following point:

- lower temperature within a suitable range and upper temperature within a suitable range

$79-82\left({ }^{\circ} \mathrm{C}\right)$$84-88\left({ }^{\circ} \mathrm{C}\right)$

Do not award a range which starts or ends with $83\left({ }^{\circ} \mathrm{C}\right)$

(1)