Alcohols (Cambridge (CIE) AS Chemistry): Exam Questions

Alcohol A has the formula (CH₃)₃CCH(OH)CH₃ and alcohol B has the formula (CH₃)₃CCH₂CH₂OH

i) Draw the displayed formula of alcohol A and state its name in Table 1.1

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Table 1.1

ii) In Table 1.2 draw the displayed formula of the organic product formed when alcohol A is heated under reflux with acidified potassium dichromate(VI) 

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Table 1.2

iii) When alcohol B is heated under reflux with acidified potassium dichromate(VI), a different organic product is formed. 

• Draw the displayed formula of this product in Table 1.3 

Table 1.3

• Explain why this product is different to the one formed in part (ii)

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2-bromobutane can be prepared by the following reaction:

CH₃CH(OH)CH₂CH₃ + Br^- → CH₃CH(Br)CH₂CH₃ + OH^- 

i) Name the type of reaction occuring.

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ii) Suggest suitable reagents for this reaction.

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Explain why both alcohols A and B are soluble in water.

Alcohols A and B are heated with an alkaline solution of iodine. Complete Table 1.4 stating the observations of for each alcohol.

Table 1.4

When pentan-2-ol reacts with concentrated phosphoric acid under reflux, three alkenes are formed, X, Y and Z.

X and Y are stereoisomers of one another.

Draw the structures of alkenes, X, Y and Z.

State how the stereoisomers formed in part (a) arise.

Pentan-2-ol can undergo different reactions. Write the equations for the reaction of pentan-2-ol with the following reagents. You do not need to include state symbols

i) Oxygen ..........................................................................................................

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ii) Sodium ..........................................................................................................

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iii) Phosphorus(V) chloride ..........................................................................................................

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Pentan-2-ol can undergo oxidation when reacted with potassium dichromate(VI) to form a ketone. 

Draw and label the apparatus which would be necessary to ensure that pentan-2-ol was oxidised to the ketone.

This question is about the formation of alcohols.

2-bromobutane reacts with OH^– in aqueous conditions to produce alcohol A. 

Draw the structure of alcohol A

Draw the reaction mechanism for the formation of alcohol A in part (a).

Alcohol A reacts with ethanoic acid in the presence of concentrated sulfuric acid to form compound B. Draw the structurs of compound B.

Both alcohol A and water can act as weak acids. Explain why alcohol A is a weaker acid than water.

Butan-1-ol can be oxidised by acidified potassium manganate(VII), KMnO₄ , using two different methods.

In the first method, butan-1-ol is added dropwise to acidified potassium manganate(VII), KMnO₄ and the product is distilled off immediately.

Using the symbol [O] for the oxidising agent, write an equation for this oxidation of butan-1-ol, showing clearly the structure of the product.

State what colour change you would observe ..................................................

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Equation ...........................................................................................................

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In a second method, the mixture of butan-1-ol and acidified potassium manganate(VII), KMnO₄ ,is heated under reflux.

Identify the product which is obtained by this reaction.

Give the structures and names of two branched chain alcohols which are both isomers of butan-1-ol. Only Isomer 1 is oxidised when warmed with acidified potassium manganate(VII).

Write the half equation for the reduction of MnO₄^-  in this reaction.

Four reactions on butan-2-ol are shown below

• Reaction 1: Butan-2-ol compound A

• Reaction 2: Butan-2-olcompound B + HCl + SO₂

• Reaction 3: Butan-2-ol compound C

• Reaction 4: Butan-2-ol 2-chlorobutane

Compound A is a stereoisomer of cis-but-2-ene.

 i) Draw the structure of the stereoisomer of cis-but-2-ene. 

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 ii) Explain why compound A is less soluble than butan-2-ol. 

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The reaction to form 2-chlorobutane produces three products.

 i) State the name of reagent Y. 

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 ii) Give the formulae of the two other products formed in this reaction.  

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Give the equation for the overall reaction between butan-2-ol and phosphorus tribromide which occurs at room temperature.

Draw the structure of compound B and identify reagent X.

The structure of glycolic acid is shown in Fig. 2.1.

Fig. 2.1

Complete Table 2.1 to show what you would observe when an aqueous solution of glycolic acid is added separately to each of the reagents. If a reaction occurs, state the functional group of glycolic acid that is responsible for the reaction.

Table 2.1

Glycolic acid can also be made by reacting glyoxylic acid with NaBH₄ as shown in Fig. 2.2.

Fig. 2.2

i) State the role of NaBH₄ in this reaction.

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 ii) Write an equation for this reaction using molecular formulae. Use [H] to represent NaBH₄. 

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iii) Explain why NaBH₄ is a suitable reducing agent for this reaction. 

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When glycolic acid is heated in the presence of a sulfuric acid catalyst, a new compound, Y, C₄H₄O₄, is formed. The equation for the reaction is given.

The infrared spectrum of Y is shown in Fig. 2.3.

Fig. 2.3

i) State how this spectrum differs from an infra-red spectrum of glycolic acid. Using Table 2.1, explain your answer with particular reference to the peaks within the range 1500 – 4000 cm^–1.

Table 2.1

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ii) Suggest a structure for Y. 

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Compounds W, X and Y are all straight chain carbohydrates with X and Y each containing five carbons. Compound W and a by-product, compound Z, are formed from the reaction between compound X and Y.

Compound X can be fully oxidised by the reaction with acidified potassium manganate(VII) to give compound Y. 5.508 g of compound Y contains 0.054 moles.

State the name of compound Y. Justify your answer.

i) Draw the full displayed formula of compound W 

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ii) Explain how compound Z is formed in the reaction 

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Compound X will oxidise to compound Y if allowed to fully oxidise.

Explain how a student could stop the full oxidation of compound X.

i) Write the structural formula of an isomer of compound X that will not react with acidified potassium manganate(VII).

ii) Using your knowledge of bonds present in the oxidation products of different classes of alcohols, suggest why the isomer you have drawn will not react with acidified potassium manganate(VII).