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

Jul 28, 2017

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

#### Explanation:

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:

$\boldsymbol{\underline{\text{Aldehyde"color(white)(....)Scolor(white)(.....)"Ketone} \textcolor{w h i t e}{m m m} S}}$
"propanal"color(white)(.......)20color(white)(... ,.)"propanone"color(white)(mm)∞
$\text{butanal"color(white)(...,....)7.6color(white)(.,,)"butanone} \textcolor{w h i t e}{\ldots . , .} 26$
$\text{pentanal"color(white)(.......)1.2color(white)(,.,)"pentan-2-one} \textcolor{w h i t e}{\ldots} 6$
$\text{hexanal"color(white)(........)0.6color(white)(,.,)"hexan-2-one} \textcolor{w h i t e}{. ,} 1.4$

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