How does the solubility of aldehydes and ketones change in water as the number of carbon atoms changes?

Answer 1

The solubilities of both aldehydes and ketones in water decrease as the number of carbon atoms increases.

However, alkyl groups are electron-donating groups, so ketones are more polar than aldehydes.

Thus, ketones are slightly more soluble than aldehydes with the same number of carbon atoms.

Here's a table of the solubilities #S# (in g/100 mL) for some aldehydes and ketones:

#bbul("Aldehyde"color(white)(....)Scolor(white)(.....)"Ketone"color(white)(mmm)S)#
#"propanal"color(white)(.......)20color(white)(... ,.)"propanone"color(white)(mm)∞#
#"butanal"color(white)(...,....)7.6color(white)(.,,)"butanone"color(white)(....,.)26#
#"pentanal"color(white)(.......)1.2color(white)(,.,)"pentan-2-one"color(white)(...)6#
#"hexanal"color(white)(........)0.6color(white)(,.,)"hexan-2-one"color(white)(.,)1.4#

The dividing line for "soluble" is about four carbon atoms for aldehydes and five carbon atoms for ketones.

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Answer 2

Kai Bowman

Solubility generally decreases with increasing carbon atoms due to a decrease in polarity.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.