Deduce the order of increasing solubility in water of the three compounds.

Explain your reasoning.

\({\text{butane}} < {\text{propanal}} < {\text{ethanoic acid}}/{\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_2}{\text{C}}{{\text{H}}_3} < {\text{C}}{{\text{H}}_3}{\text{C}}{{\text{H}}_2}{\text{CHO}} < {\text{C}}{{\text{H}}_3}{\text{COOH}}\);

all three compounds have similar molar masses;

butane non-polar so no attraction to water molecules/insoluble;

propanal polar so can form some interactions with water molecules;

ethanoic acid can form (more) hydrogen bonds with water molecules / OWTTE;

Award [1 max] for butane is non-polar and propanal and ethanoic acid are both polar.

The order of solubility of butane, propanal and ethanoic acid in water was generally correctly given in (a), but candidates had trouble explaining it, often just discussing functional groups or polarity, without referring to interactions with water in (b). Many referred to the length of the carbon chain. It was apparent that the concept of solubility was poorly understood. Responses were often not an explanation but merely a repetition of the order stated in (a).

The order of solubility of butane, propanal and ethanoic acid in water was generally correctly given in (a), but candidates had trouble explaining it, often just discussing functional groups or polarity, without referring to interactions with water in (b). Many referred to the length of the carbon chain. It was apparent that the concept of solubility was poorly understood. Responses were often not an explanation but merely a repetition of the order stated in (a).