Final answer:
Hydrates contain water in their crystal lattice, which can be determined by heating and weighing the compound to find the percent of water. Changes in color of hydrates, such as cobalt (II) chloride and copper sulphate upon heating, help in identifying the anhydrous form. Adding silver nitrate to unknown salts can indicate the presence of certain ions when precipitates form.
Step-by-step explanation:
Hydrates are ionic compounds that include water molecules integrated into their crystal lattice structure. The presence of water often results in hydrates being of different colors than their anhydrous counterparts. To determine the percent of water in a hydrate, one can heat the compound to remove the water, then weigh the products to calculate the water content. This process is critical in understanding chemical formulations and reactions.
For example, Cobalt (II) chloride exists in two forms: as a blue anhydrous compound and as a magenta hydrate with six water molecules in its formula, known as cobalt (II) chloride hexahydrate (CoCl₂·6H₂O). When copper sulphate is heated, its blue-colored crystals lose water and turn white. Similarly, when anhydrous CoCl₂ is exposed to moisture, it absorbs water and changes color, indicating its usage as a humidity indicator.
When identifying unknown salts, experiments involving the addition of agents like silver nitrate may result in a precipitate forming, which suggests the presence of certain ions such as chlorides or carbonates. In the case of a clear, colorless salt solution where the addition of silver nitrate results in a pale yellow precipitate, followed by the addition of chlorine water and carbon tetrachloride turning the solution purple, the salt is likely a halide.