Final answer:
A metal will not always replace another metal in a compound; it depends on the metal's reactivity according to the activity series. For instance, magnesium can replace copper in a compound because it is more reactive, but copper cannot replace iron.
Step-by-step explanation:
No, a metal will not always replace another metal in a compound dissolved in water. This process is dependent on the activity series of metals. In a single-replacement reaction, a metal can only replace another metal if it is more reactive, according to the activity series. For example, when magnesium is placed in an aqueous solution of copper (II) nitrate, it replaces the copper because magnesium is more reactive.
In the activity series, metals listed above others can replace those below them. This means that iron can replace copper in a solution of copper sulfate to form iron sulfate and elemental copper because iron is above copper in the series. However, copper cannot replace iron in iron sulfate. Similarly, active metals like potassium react vigorously with water to form metal hydroxides and hydrogen gas.
Conversely, in a double-replacement reaction, the exchange of ions occurs without a change in oxidation numbers, and for a reaction to proceed, a product must precipitate. Furthermore, it's important to note that a metal cannot replace a nonmetal in a compound; each type of element will generally replace its kind.
When working with chemistry problems involving reactions, it is essential to refer to the activity series to predict whether a single-replacement reaction will occur. This series is a practical tool that lets us understand and forecast the outcomes of potential reactions between elements and compounds in aqueous solutions.