Hydrates are compounds that contain water molecules within their structure. These water molecules are chemically bonded to the substance, often forming a specific ratio with the other components. Common examples of hydrates include copper(II) sulfate pentahydrate, which has five water molecules for each copper sulfate unit, and calcium sulfate dihydrate, which contains two water molecules. When hydrates are heated, they can lose their water content in a process called dehydration, resulting in an anhydrous form of the compound. This property is important in various applications, such as in construction materials and pharmaceuticals, where the presence or absence of water can significantly affect performance and stability.