A-Level Edexcel Chemistry Organic Functional Group Tests

Review A-Level Edexcel Chemistry organic functional group tests through reagent choices, positive observations and inference from practical results.

[Maximum number: 2]

Cyclohexene may be prepared from cyclohexanol using 85\% phosphoric(V) acid.

Figure for Question 3.P16—Tests for organic functional groups question 1 — Edexcel A-Level Chemistry AS

A simplified procedure for this preparation is shown.
Step 1 Accurately weigh about 4 g of cyclohexanol into a pear-shaped flask.
Step 2 Add about $0.5 \mathrm{~cm}^{3}$ of 85% phosphoric(V) acid and a few anti-bumping granules to the flask.

Step 3 Set up the apparatus for fractional distillation.
Step 4 Heat the flask and collect the distillate that contains impure cyclohexene and water.

Step 5 Separate the impure cyclohexene and water, using a separating funnel.
Step 6 Add a few granules of anhydrous calcium chloride to the impure cyclohexene and allow the mixture to stand.

Step 7 Decant the impure cyclohexene into a clean pear-shaped flask. Distil the cyclohexene and weigh the distillate.

Data

Table for Question 3.P16—Tests for organic functional groups question 1 — Edexcel A-Level Chemistry AS

Separate samples of cyclohexanol and the cyclohexene product were tested with phosphorus(V) chloride and with bromine water.

Complete the table to show the observations.

An answer that makes reference to the following points:

- any three correct observations

- fourth correct observation

\multirow{2}{*}{ Test } & \multicolumn{2}{|c|}{ Observations }

\cline { 2 - 3 } & cyclohexanol & cyclohexene

addition of

phosphorus(V)

chloride

steamy / misty /

white fumes

no change / no

reaction /

no observation

addition of

bromine water

brown /orange /

yellow $\mathrm{Br}_{2}($ aq )

unchanged

brown / orange /

yellow $\mathrm{Br}_{2}($ aq)

turns colourless

\end{tabular}

For $\mathrm{PCl}_{5}$ do not award white smoke

For $\mathrm{Br}_{2}(\mathrm{aq})$ and cyclohexanol allow no change / no reaction / no observation

For $\mathrm{Br}_{2}(\mathrm{aq})$ and cyclohexene allow just 'decolorised' / ‘turns colourless’

Do not award red or red-brown for colour of $\mathrm{Br}_{2}(\mathrm{aq})$

Do not award additional incorrect observations
\end{tabular}

(2)

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3.P16—Tests for organic functional groups question 1