Alcohols — Structured Questions (Cambridge International AS Chemistry): Exam Questions

Construct an equation for the complete combustion of butan-1-ol.

A reaction scheme for some reactions of butan-2-ol is shown in Fig. 1.1.

Fig. 1.1

State the reagents and conditions required for:

i) Reaction 1

ii) Reaction 3

Extract:

A reaction scheme for some reactions of butan-2-ol is shown in Fig. 1.1.

Reaction 1 forms but-2-ene Reaction 2 is refluxing with acidified K2Cr2O7 to form compound A Reaction 3 forms 2-bromobutane

State the systematic name of compound A.

Complete Table 2.1 to classify each alcohol as primary, secondary or tertiary.

Table 2.1

Construct an equation for the dissociation of:

i) water

ii) butan-1-ol

Explain why alcohols are weaker acids than water.

Three different alcohols, A, B and C are shown in Fig. 3.1.

Fig. 3.1

State the systematic name of alcohol C and whether it is primary, secondary or tertiary.

Extract:

Three different alcohols, A, B and C are shown in Fig. 3.1.

{align=center} Fig. 3.1

Alcohol A is heated under reflux with acidified potassium dichromate(VI).

i) State the systematic name of the organic product formed.

ii) State the colour change observed in this reaction.

Extract:

Three different alcohols, A, B and C are shown in Fig. 3.1.

{align=center} Fig. 3.1

Alcohols A, B and C are each heated separately with alkaline I₂ (aq). Identify which alcohol gives a yellow precipitate.

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.

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

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 and explain why this product is different to the one formed in part (ii)

2-bromobutane can be prepared from butan-2-ol.

i) Name the type of reaction occurring.

ii) Suggest suitable reagents for this reaction.

Extract:

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

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

Extract:

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

Alcohols A and B are each heated separately with alkaline I₂(aq). State the observations for each alcohol.

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 skeletal structures of alkenes, X, Y and Z.

Extract:

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.

Explain the origin of the stereoisomerism shown by the alkenes X and Y in part (a).

Construct an equation for the reaction of pentan-2-ol with:

i) oxygen

ii) sodium

iii) phosphorus(V) chloride

Pentan-2-ol can be oxidised to a ketone by heating under reflux with acidified potassium dichromate(VI). Draw a labelled diagram of the apparatus used.

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

Draw the structural formula of alcohol A.

Extract:

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

Draw the reaction mechanism for the formation of alcohol A in part (a). Include charges, dipoles, lone pairs of electrons and curly arrows, as appropriate.

Extract:

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

The structural formula of alcohol A is butan-2-ol.

Alcohol A is heated under reflux with ethanoic acid and a concentrated sulfuric acid catalyst to form compound B.

Draw the structure of compound B.

Extract:

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

The structural formula of alcohol A is butan-2-ol (a secondary alcohol with the –OH group at position 2).

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) using two different methods.

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

i) State the colour change observed in the reaction mixture.

ii) Construct an equation for this reaction. Use [O] to represent one atom of oxygen from the oxidising agent.

In a second method, butan-1-ol is heated under reflux with acidified potassium manganate(VII).

State the systematic name of the organic product formed.

Draw the structural formulae and state the systematic names of two branched-chain isomers of butan-1-ol, Isomer A and Isomer B. Only Isomer A is oxidised when warmed with acidified potassium manganate(VII).

Construct an ionic half-equation for the reduction of MnO₄^- in acidic conditions.

Four reactions on butan-2-ol are shown below

• Reaction 1: Butan-2-ol -> from Heat to H _ 3 PO _ 4 of compound A
• Reaction 2: Butan-2-ol-> from _ to reagent X ofcompound B + HCl + SO₂
• Reaction 3: Butan-2-ol -> from room temp to PBr _ 3 ofcompound C
• Reaction 4: Butan-2-ol -> from room temp to reagent Y of2-chlorobutane

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

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

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

Extract:

Four reactions on butan-2-ol are shown below

• Reaction 1: Butan-2-ol $$\rightarrow_{Heat}^{H_{3} PO_{4}}$$ compound A
• Reaction 2: Butan-2-ol$$\rightarrow_{}^{reagent \mathbf{X}}$$compound B + HCl + SO2
• Reaction 3: Butan-2-ol $$\rightarrow_{room temp}^{PBr_{3}}$$compound C
• Reaction 4: Butan-2-ol $$\rightarrow_{room temp}^{reagent \mathbf{Y}}$$2-chlorobutane

The reaction of butan-2-ol with reagent Y produces three products.

i) State the name of reagent Y.

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

Extract:

• Reaction 3: Butan-2-ol $$\rightarrow_{room temp}^{PBr_{3}}$$compound C

Construct an equation for the overall reaction between butan-2-ol and phosphorus tribromide.

Extract:

Four reactions on butan-2-ol are shown below

• Reaction 1: Butan-2-ol $$\rightarrow_{Heat}^{H_{3} PO_{4}}$$ compound A
• Reaction 2: Butan-2-ol$$\rightarrow_{}^{reagent \mathbf{X}}$$compound B + HCl + SO2
• Reaction 3: Butan-2-ol $$\rightarrow_{room temp}^{PBr_{3}}$$compound C
• Reaction 4: Butan-2-ol $$\rightarrow_{room temp}^{reagent \mathbf{Y}}$$2-chlorobutane

i) Identify reagent X.

ii) Draw the structure of compound B.

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 reagent. If a reaction occurs, state the functional group of glycolic acid 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.

ii) Construct an equation for this reaction using molecular formulae. Use [H] to represent one atom of hydrogen from the reducing agent.

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

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.

2CH₂(OH)CO₂H → C₄H₄O₄ + 2H₂O

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

ii) Suggest a structure for Y.

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 compounds X and Y.

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

Deduce the systematic name of compound Y. Justify your answer.

Extract:

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 compounds X and Y.

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

i) Draw the displayed formula of compound W.

ii) Explain how compound Z is formed in the reaction.

Extract:

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 compounds X and Y.

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

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

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

Extract:

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 compounds X and Y.

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

Compound Y name = Pentanoic acid

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

ii) Suggest why this isomer will not react with acidified potassium manganate(VII).