Moles Notes

This set covers vocabulary and concepts related to calculating the formula of chemical hydrates based on laboratory mass measurements.

Hydrate

A compound that holds a specific amount of water within its crystalline structure, such as the lead (II) and $CaSO_4$ samples mentioned in the text.

Anhydrous compound

The substance that remains after all the water of hydration has been driven off from a hydrate, typically through heating in a crucible.

Water of hydration

The water molecules that are chemically bound into a hydrate and can be removed by heating, such as the $0.505\,g$ of water driven off from the $2.515\,g$ sample of $CaSO_4$.

Crucible

A laboratory vessel, often mentioned with a cover, used to contain a hydrate sample while it is being heated to determine the change in mass.

Formula of a hydrate

A mathematical representation of a hydrate showing the ratio of the anhydrous salt to water, calculated by comparing the mass before and after heating (e.g., finding the ratio for a $1.203\,g$ sample that weighs $1.142\,g$ after heating).

$$CaSO_4$$

Calcium sulfate; an ionic compound used in the text as an example where a $2.515\,g$ hydrate sample lost $0.505\,g$ of water upon heating.