Organic Chemistry II: Carboxylic Acids (Edexcel A Level Chemistry): Exam Questions

This question is about lactic acid (2-hydroxypropanoic acid), CH₃CH(OH)COOH. Lactic acid is used to make biodegradable polymers.

Lactic acid can be made in a two-step synthesis starting from ethanal, CH₃CHO.

Devise a reaction scheme for a two-step synthesis.

Include in your answer all reagents and conditions, the type of reaction occurring at each step, and a balanced equation for each reaction. State symbols are not required.

Polymerisation of lactic acid forms poly(lactic acid) as shown in the diagram.

i) State the type of polymerisation occurring in this reaction.

(1)

ii) On the diagram, draw a circle around the repeat unit of the polymer.

(1)

This question is about esters with the molecular formula C₆H₁₂O₂.

Propyl propanoate has the structure shown.

Devise a synthetic pathway to prepare propyl propanoate starting with 1-bromopropane as the only organic compound.

Include the reagents for each step in the synthesis, and the names or structures of the intermediate compounds.

Another ester, A, with molecular formula C₆H₁₂O₂, was hydrolysed.

It produced ethanoic acid, and an alcohol, B, with molecular formula C₄H₁₀O.

Alcohol B undergoes an elimination reaction to produce a mixture of but-1-ene and but-2-ene.

Deduce the structures of B and A. Justify your structure of B.

This question is about the identification of some organic compounds.

The skeletal formulae of four organic compounds are shown.

i) Which of these compounds can be hydrolysed to form methanol as one of the products?

(1)

ii) Which of these compounds produces carbon dioxide when it reacts with aqueous sodium hydrogencarbonate?

(1)

Compound T, C₄H₁₀O, is oxidised by acidified potassium dichromate(VI) to form compound U, C₄H₈O.

U gives an orange precipitate with 2,4-dinitrophenylhydrazine (Brady’s reagent) but does not give a red precipitate when heated with Fehling’s solution.

T reacts with ethanoyl chloride to form compound V, C₆H₁₂O₂ .

Deduce the structures of compounds T, U and V. Justify your answers.

The compound flavan-3-ol is found in tea, fruit and wine.  

Clearly label all the chiral carbon atoms in flavan-3-ol. 

Give the molecular formula for flavan-3-ol.  

A sample of flavan-3-ol extracted from wine contained some ethanol. The sample was left in a flask, open to the air for several days. The contents were then analysed to identify any new compounds formed. Several new compounds were found to be present, including some with a distinctive fruity smell.

Identify four new organic compounds that could form under these conditions by considering the chemistry of alcohols. Justify your answers. Include the structure of two compounds formed from flavan-3-ol, one of which has a fruity smell. 

This question is about polymers.

Compare and contrast how each of these monomers forms a polymer.

Include equations, showing the formation of a single repeat unit for each polymer.

Give three ways in which waste polymers can be utilised to improve their sustainability.

This question is about a dicarboxylic acid Y which is present in some citrus fruits. Y contains only the elements carbon, hydrogen and oxygen.

A sample of Y with a mass of 1.98 g was burned completely in excess oxygen. The reaction formed 2.51 g of carbon dioxide, CO₂, and 0.69 g of water, H₂O.    

Use these data to calculate the empirical formula of Y.

A solution was prepared using 4.34 g of the dicarboxylic acid Y made up to a volume of 250 cm³ with distilled water.

A 25.0 cm³ sample of this solution was then titrated using sodium hydroxide solution, NaOH (aq), of concentration 0.320 mol dm^−3.

The mean titre of sodium hydroxide solution was 26.10 cm³.

Calculate the molar mass of Y using the titration data, and hence deduce its structure. You must show your working.

Which of these is used to convert a dicarboxylic acid into a diol?

Propanoic acid can be converted to propanoyl chloride.

Name the reagent used and write an equation for this reaction.

Propanoyl chloride reacts with ethanol to form an ester.

Write an equation for this reaction and name the organic product.