Summary
Highlights
Hydrates are ionic compounds or ionic salts that can trap water molecules within their crystalline structure. These trapped water molecules are caged by the positive and negative ions of the salt, leading to the term 'hydrated salts'.
To name a hydrate, first name the ionic compound as usual. Then, determine the number of water molecules (H₂O) present and use a numerical prefix (e.g., 'di' for two, 'hepta' for seven) followed by 'hydrate'. The dot between the ionic compound and H₂O in the formula indicates 'contains' and does not mean multiplication.
For CuCl₂·2H₂O, the ionic compound is copper(II) chloride. Since there are two water molecules (2H₂O), the prefix 'di' is used, making the full name copper(II) chloride dihydrate.
For ZnSO₄·7H₂O, the ionic compound is zinc sulfate. With seven water molecules (7H₂O), the prefix 'hepta' is used, resulting in the name zinc sulfate heptahydrate.
To write the formula for a hydrate, first write the formula for the ionic compound. Then, identify the prefix for 'hydrate' to determine the number of water molecules. Connect the ionic compound formula and the water molecules with a dot (·) to indicate it's a hydrated salt.
For copper(II) sulfate pentahydrate, the ionic compound is copper(II) sulfate, so the formula is CuSO₄. 'Penta' indicates five water molecules (5H₂O). The complete formula is CuSO₄·5H₂O.