Question #fc437

Oct 29, 2016

Sugar dissolves in water because its $\text{OH}$ groups form strong hydrogen bonds with water.

Explanation:

The formula for sucrose is

It contains eight $\text{O-H}$ groups.

The oxygen atoms are slightly negative, and the hydrogen atoms are slightly positive.

That is, the $\text{O-H}$ bonds are polar.

Sucrose molecules are attracted to each other in the crystal because of the dipole-dipole attractions among the $\text{O}$ atoms in one molecule and the $\text{H}$ atoms in the neighbouring molecules (hydrogen bonds).

If we add water to sucrose, the $\text{O-H}$ groups in the water form hydrogen bonds to the sucrose molecules in the crystal.

In turn, the sucrose molecules use their $\text{O-H}$ groups to form $\text{H}$-bonds with the water molecules.

We see below a picture of water molecules attacking the surface of sucrose.

The water molecules surround the sucrose molecules, replacing the sucrose-sucrose $\text{H}$-bonds with sucrose-water $\text{H}$-bonds.

Eventually, the sucrose molecules leave the surface of the crystal and disperse themselves throughout the water as hydrated sucrose molecules.