Salt & Boiling Water

[naz_nomad]

When I drop a small amount of salt in a pan of boiling water, why does it fizz like mad for a few seconds?

thanks ... Naz

[brachiopod]

The water at the base of your pan is slightly super heated. That means that it is at a temperature above its boiling point - the point at which bubbles start erupting in the liquid.

In a boiling liquid, bubbles form as the water turns from the liquid state to the gaseous state.
In the enclosed pan, the layer of water at the bottom of the pan closest to heat source wants to form bubbles as it boils, but they don't form that easily as they usually like something to form around. The water continues to heat up above its boiling point (becomes super-heated) until the system eventually gives for a moment, and large boiling bubbles form.

By adding salt, you are giving the 'boiling bubbles' something to form around, and their addition to the super-heated water causes a flurry of bubbles to form.

Chemists use this principle. The formation of large unpredicatable bubbles in a boiing liquid, (known as 'bumping'), is undesiarable in an experiment. The addition of small glass beads - similar in size to grains of salt, result in a gentle, steady stream of small bubbles when the liquid boils.

This, of course, is not the reason we add salt to cooking water, as the salt dissolves almost immediately.

[naz_nomad]

Fantastic answer ... thank you