Why are alkanes insoluble in water?

Alkanes are insoluble in water because they are non-polar molecules, while water is a polar molecule.

Alkanes are hydrocarbons, which means they are composed of hydrogen and carbon atoms. The bonds between these atoms are covalent and share electrons equally, resulting in a non-polar molecule. Non-polar molecules have an even distribution of electrical charge, so there is no region of positive or negative charge that could interact with polar molecules.

On the other hand, water is a polar molecule. This means it has a region of positive charge and a region of negative charge due to the unequal sharing of electrons between the oxygen and hydrogen atoms. The oxygen atom attracts the shared electrons more strongly, creating a partial negative charge on the oxygen end and a partial positive charge on the hydrogen end.

The principle of 'like dissolves like' applies here. Polar substances tend to dissolve other polar substances, and non-polar substances tend to dissolve other non-polar substances. This is because the intermolecular forces of attraction between similar types of molecules are stronger. In the case of alkanes and water, the polar water molecules are more attracted to each other than to the non-polar alkane molecules. Similarly, the non-polar alkane molecules are more attracted to each other than to the polar water molecules.

Therefore, when you try to mix alkanes with water, they do not dissolve. Instead, they separate into two distinct layers, with the less dense alkanes floating on top of the water. This is a clear demonstration of the insolubility of alkanes in water due to their non-polar nature.