Quick questions on Organic synthesis and analysis - WJEC A-Level Chemistry

A workable mental map of the common one-step conversions is: alkene to alcohol (steam, acid catalyst); alcohol to halogenoalkane (HX or $\text{PCl}_5$); halogenoalkane to nitrile (KCN, lengthens the chain) or to amine (excess ammonia); nitrile to amine ($\text{LiAlH}_4$) or to carboxylic acid (hydrolysis); primary alcohol to aldehyde (distil) to carboxylic acid (reflux); secondary alcohol to ketone; carbonyl to hydroxynitrile (HCN); acid to ester (alcohol plus acid catalyst) or to acyl chloride ($\text{SOCl}_2$). Choosing the right path means matching the carbon skeleton and the oxidation level of the target.

Selecting the correct technique, and saying why, is as important in the exam as the reaction chemistry itself.

A multi-step route from phenol to salicylic acid to aspirin, followed by recrystallisation and a melting-point check, mirrors the planning and purity assessment tested here. Pharmaceutical purity control. Drug manufacturers combine recrystallisation, chromatography and melting-point determination to certify that an active ingredient meets strict purity standards before release.

State the technique used to purify an impure organic solid. [1 mark]

State what a sharp melting point at the literature value indicates. [1 mark]

Calculate the percentage yield if $3.0$ g of product is made from a theoretical maximum of $5.0$ g. [1 mark]

State the reagent that lengthens a carbon chain by one carbon when reacted with a halogenoalkane. [1 mark]

State how an impurity affects the melting point of a solid. [1 mark]