Vitamin A contains retinol. Under appropriate conditions, acidified $$$\mathrm{KMnO}_{4}(\mathrm{aq})$$$ can be used to break $$$\mathrm{C}=\mathrm{C}$$$ bonds. After these bonds have been broken, further oxidation of the fragments may occur. Under which conditions is the acidified $$$\mathrm{KMnO}_{4}(\mathrm{aq})$$$ used and what do the final oxidation products include?

Chemistry

IGCSE&ALevel

CAIE

Exam No：9701_w24_qp_11 Year：2024 Question No：29

Answer:

Knowledge points:

17.1.1.1 the oxidation of primary alcohols using acidified and distillation to produce aldehydes

17.1.1.2 the oxidation of secondary alcohols using acidified or acidified and distillation to produce ketones

17.1.2.1 the reduction of aldehydes and ketones, using to produce alcohols

17.1.2.2 the reaction of aldehydes and ketones with HCN, KCN as catalyst, and heat to produce hydroxynitriles exemplified by ethanal and propanone

17.1.3 describe the mechanism of the nucleophilic addition reactions of hydrogen cyanide with aldehydes and ketones in 17.1.2(b)

17.1.4 describe the use of 2,4-dinitrophenylhydrazine (2,4-DNPH reagent) to detect the presence of carbonyl compounds

17.1.5 deduce the nature (aldehyde or ketone) of an unknown carbonyl compound from the results of simple tests (Fehling’s and Tollens’ reagents; ease of oxidation)

17.1.6 deduce the presence of a – group in an aldehyde or ketone, , from its reaction with alkaline (aq) to form a yellow precipitate of tri-iodomethane and an ion,

7.2.1 state the names and formulae of the common acids, limited to hydrochloric acid, HC/, sulfuric acid, ethanoic acid,

7.2.10 select suitable indicators for acid-alkali titrations, given appropriate data

7.2.2 state the names and formulae of the common alkalis, limited to sodium hydroxide, NaOH, potassium hydroxide, KOH, ammonia,

7.2.3 describe the Brønsted–Lowry theory of acids and bases

7.2.4 describe strong acids and strong bases as fully dissociated in aqueous solution and weak acids and weak bases as partially dissociated in aqueous solution

7.2.5 appreciate that water has pH of 7, acid solutions pH of below 7 and alkaline solutions pH of above 7

7.2.6 explain qualitatively the differences in behaviour between strong and weak acids including the reaction with a reactive metal and difference in pH values by use of a pH meter, universal indicator or conductivity

7.2.7 understand that neutralisation reactions occur when

7.2.8 understand that salts are formed in neutralisation reactions

7.2.9 sketch the pH titration curves of titrations using combinations of strong and weak acids with strong and weak alkalis

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