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ASChemistryEdexcelExam Questions3. Organic Chemistry3.5 Alcohols

Alcohols (Edexcel AS Chemistry)

Exam Questions

31 mins3 questions
Medium
Hard
1a2 marks

This question is about some reactions of alcohols.  

i)
Which alcohol cannot be oxidised by acidified potassium dichromate(Vl)?  
(1)
  ☐ A hexan-2-ol  
  ☐ B 2-methylpentan-2-ol  
  ☐ C hexan-3-ol 
  ☐ D 2-methylpentan-3-ol 

ii)
Which alcohol reacts with iodine in the presence of alkali to form a yellow solid? 
(1)
  ☐ A hexan-2-ol  
  ☐ B 2-methylpentan-2-ol  
  ☐ C hexan-3-ol 
  ☐ D 2-methylpentan-3-ol 

   

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1b1 mark

Which reagent is used with iodine to prepare iodoalkanes from alcohols? 

  ☐ A red phosphorus 
  ☐ B concentrated phosphoric acid 
  ☐ C sulfur 
  ☐ D concentrated sulfuric acid 

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2a8 marks

1-bromobutane can be prepared from butan-1-ol and hydrogen bromide.

CH3CH2CH2CH2OH + HBr rightwards arrowCH3CH2CH2CH2Br + H2O

Hydrogen bromide can be made from sodium bromide and 50% concentrated sulfuric acid.

The steps for the preparation of impure 1-bromobutane are summarised.

Step 1

Dissolve the sodium bromide in distilled water in a pear-shaped flask and then add 20.0 cm3 of butan-1-ol.
Step 2

Surround the flask with an ice bath to cool the mixture, before adding concentrated sulfuric acid drop by drop.
Step 3

Remove the flask from the ice bath and add a few anti-bumping granules to the reaction mixture.
Step 4

Set up the apparatus for heating under reflux. Heat the mixture in the flask for 30 minutes and then allow the apparatus to cool.
Step 5

Rearrange the apparatus for distillation and heat the mixture until no more 1-bromobutane distils over.


i)
Parts of the method are given in bold type in Steps 2, 3 and 4.
Give a reason why each of these parts is necessary.

(3)

ii)
A student drew a diagram of the apparatus used for heating under reflux in Step 4.
There are three errors in the apparatus shown in the diagram.
Assume the apparatus is suitably clamped.

q8aii-9cho-al-3-june-2019-qp-edexcel-a-level-chem

Identify the three errors, including the effect of each error.

(3)

iii)
The student corrected the errors.
While the mixture was heating under reflux, the student noticed a small amount of a brown vapour was formed.

Explain why the brown vapour forms.
(2)

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2b
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The distillate collected in Step 5 is a mixture consisting of two layers.
There is an aqueous layer and a layer containing impure 1-bromobutane.

Data

Densities:

water                       1.00 g cm-3

butan-1-ol              0.81 g cm-3

1-bromobutane     1.27 g cm-3

Boiling temperature of 1-bromobutane = 102 °C

The steps for the purification of the 1-bromobutane are summarised.

Step 6

Transfer the mixture from Step 5 to a separating funnel and remove the aqueous layer.
Step 7

Wash the impure 1-bromobutane with concentrated hydrochloric acid in the separating funnel. Remove the aqueous layer.
Step 8

Add aqueous sodium hydrogencarbonate to the impure 1-bromobutane in the separating funnel.
Step 9

Shake the mixture in the separating funnel and, from time to time, invert the funnel and open the tap.
Step 10 Collect the 1-bromobutane layer from Step 9 in a small conical flask.
Add anhydrous sodium sulfate and swirl the flask until the liquid becomes clear.
Step 11

Decant the 1-bromobutane into a clean pear-shaped flask and redistil it.
Measure the volume of 1-bromobutane produced.
i)
State the position of the aqueous layer in the separating funnel at the start of Step 6. Justify your answer.
(1)
ii)
Concentrated hydrochloric acid is used to remove any unreacted butan-1-ol in the mixture in Step 7.
Give the reasons for carrying out Steps 8, 9 and 10.
(3)
iii)
Give a suitable temperature range over which to collect the pure 1-bromobutane in the redistillation in Step 11.
(1)
iv)
The volume of 1-bromobutane collected was 12.0 cm3.
Calculate the number of molecules of 1-bromobutane produced in this experiment.
Give your answer to an appropriate number of significant figures.
(2)

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1a1 mark

This question is about some reactions of cyclohexanol.

q8-8cho-as-2-oct-2021-edexcel-a-level-chem

Write the skeletal formula of compound A.

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1b7 marks
i)
Give the name and displayed formula of compound B.

(2)

ii)
The infrared (IR) spectra of cyclohexanol and compound B are shown.


IR Spectrum of cyclohexanol

q8aii-8cho-as-2-oct-2021-edexcel-a-level-chem-1

IR Spectrum of compound B

q8aii-1-8cho-as-2-oct-2021-edexcel-a-level-chem

Identify the bonds, using both IR spectra, that help to confirm the reaction of cyclohexanol to produce compound B.

Your answer must include the wavenumber ranges of any relevant bonds.

(2)

iii)
The mass spectrum of compound B is shown.

q8aiii-8cho-as-2-oct-2021-edexcel-a-level-chem

Deduce the relative molecular mass of compound B using the mass spectrum.

Justify your answer.

(2)

iv)
In the mass spectrum of cyclohexanol, there is a peak at m / z = 83.

Give the formula of a fragment that could be responsible for this peak.

(2)

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1c
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i)
Cyclohexanol can be converted to cyclohexene.
What is the classification for this reaction?
(1)
  ☐ A addition
  ☐ B elimination
  ☐ C free radical substitution
  ☐ D nucleophilic substitution

ii)
In an experiment, 10.0 cm3 of cyclohexanol was converted to cyclohexene with a 63.0% yield.

Compound Molar mass / g mol–1 Density / g cm–3
cyclohexanol 100 0.962
cyclohexene 82.0

0.811

Calculate the volume of cyclohexene produced.

(4)

iii)
Cyclohexene can be prepared by reacting cyclohexanol with phosphoric(V) acid.
The mixture is warmed in a water bath for 15 minutes before distilling off a mixture of cyclohexene and water.

Devise a procedure to obtain a pure, dry sample of cyclohexene from the distillate. Include a reason for each step.

[Boiling temperature of cyclohexene = 83 °C
Density of cyclohexene = 0.811g cm–3]
(6)

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