Experiment - Water of Hydration

Vocabulary flashcards covering key terms related to hydrates, hygroscopic behavior, notation, and dehydration as described in the Water of Hydration experiment.

Hydrate

A solid in which water molecules are chemically bound to the salt's lattice in fixed molar ratios, not merely surface moisture.

Efflorescence

The tendency of a hydrate to lose water to dry air spontaneously.

Hygroscopic

Substances that absorb moisture from humid air; many are used as desiccants.

Desiccant

A material that absorbs water from the surroundings to keep things dry.

Water of hydration notation

Notation for hydrates using a dot between the salt formula and the water count, e.g., CuSO4·5H2O.

Pentahydrate

A hydrate with five water molecules per mole of salt (suffix indicating five waters), e.g., CuSO4·5H2O.

Dihydrate

A hydrate with two water molecules per mole of salt, e.g., CaCl2·2H2O.

Dehydration

Removal of water of hydration, usually by heating above 100°C (the boiling point of water).

Percent water by mass

The mass percentage of water lost during dehydration: (mass of water lost / initial mass) × 100%.

Unknown salt identification by dehydration

Heating an unknown hydrate, measuring the percent water lost, and comparing to theoretical values to identify the salt.

Theoretical hydrate formula

The expected salt·xH2O formula used as the basis for comparing experimental data.

Hydrates vs surface moisture

Hydrates contain water chemically bonded in the crystal, unlike solids with only surface-adsorbed moisture.

Goal of lab

To calculate the percent water by mass in several potential unknowns to dehydrate a solid sample and identify it by comparison to the possible unknowns