Question

Predict which of the following metals reacts with water at room temperature: (a) Li (b) \(\mathbf{M g}\) (c) \(\mathrm{Ca}\) (d) Al

Short answer

Lithium (Li) and calcium (Ca) react with water at room temperature.

Step-by-step solution

Analyze Each Metal's Reactivity

Metals can be arranged in an activity series that lists them from most reactive to least reactive. To determine which metals react with water at room temperature, we need to assess their position in this series. Metals like lithium (Li) and calcium (Ca) are high in the activity series and are known to react with water under normal conditions. On the other hand, magnesium (Mg) and aluminum (Al) tend to be less reactive with water at room temperature unless other conditions (like heating) are applied.

Examine Reaction with Water

Lithium (Li) reacts with water at room temperature, producing lithium hydroxide and hydrogen gas. Calcium (Ca) also reacts with water at room temperature, forming calcium hydroxide and hydrogen gas, although the reaction is slower compared to lithium. Magnesium (Mg) reacts very slowly with water at room temperature, and aluminum (Al) does not react with water at room temperature due to its protective oxide layer.

Identify Reactivity with Room Temperature Water

From the above analysis, the metals that react noticeably with water at room temperature are lithium (Li) and calcium (Ca). Magnesium (Mg) only reacts very slowly, and aluminum (Al) does not react.

Key concepts

Activity Series

The activity series is an essential tool for understanding the reactivity of metals. It's a list arranged by the ease with which metals undergo chemical reactions, especially with water and acids. This series ranks metals from the most reactive to the least reactive. It is an important predictor of how metals behave when exposed to different substances.

• Metals high on the activity series, like lithium (Li) and calcium (Ca), are very reactive. They can readily lose electrons, making them likely to engage in chemical reactions.
• As you move down the series, metals become less reactive. For example, magnesium (Mg) and aluminum (Al) are less reactive than lithium and calcium.
• The position of a metal in the activity series helps in predicting and understanding their chemical behavior.

This list is crucial for chemists to predict whether or not a metal will participate in a certain reaction under a given set of conditions.

Chemical Reactions with Water

Metals can have varied reactions with water, depending on their reactivity levels. When reactive metals come in contact with water, they tend to form a metal hydroxide and release hydrogen gas. This type of reaction is common among the highly reactive metals.

• Lithium (Li), being high on the activity series, reacts vigorously with water at room temperature, forming lithium hydroxide and hydrogen gas. This indicates its high reactivity.
• Calcium (Ca) also reacts with water at room temperature, although the reaction is not as fast as with lithium. Calcium hydroxide is formed, along with hydrogen gas.
• Magnesium (Mg) is less reactive at room temperature, reacting very slowly to form magnesium hydroxide and hydrogen gas.
• Aluminum (Al) is interesting as it does not react with water at room temperature. This is due to its surface being protected by a thin layer of aluminum oxide, which prevents the metal from coming in contact with water.

These differences in how metals react with water are guided by their placement on the activity series and their individual chemical characteristics.

Metal Reactivity Trends

Understanding metal reactivity trends is essential for predicting and explaining how metals will react under certain conditions. The activity series aids in this by illustrating a trend in metal reactivity.

• Highly reactive metals, such as those found at the top of the activity series, most readily undergo reactions, especially with water and acids.
• As we move down the series, metals react less vigorously. This reduction in reactivity is predictable and consistent, helping scientists understand and anticipate metal behavior.
• The reactivity trend can be influenced by an individual metal's electron configuration: those that can easily lose electrons are generally more reactive.

In summary, a metal's position in the series gives insight into how it will typically interact with substances like water, which is invaluable for both educational and practical applications in chemistry.