Question

Predict A piece of aluminum metal is placed in aqueous \(\mathrm{KCl}\) . Another piece of aluminum is placed in an aqueous \(\mathrm{AgNO}_{3}\) solution. Explain why a chemical reaction does or does not occur in each instance.

Short answer

When a piece of aluminum metal is placed in aqueous \(KCl\), no chemical reaction occurs because aluminum is less reactive than potassium. However, when aluminum is placed in an aqueous \(AgNO_3\) solution, a chemical reaction takes place as aluminum is more reactive than silver, displacing silver in the reaction: \(2 Al + 3 AgNO_3 \rightarrow 2 Al(NO_3)_3 + 3 Ag\). The relative reactivity of the metals in the activity series determines whether or not a reaction will occur in each instance.

Step-by-step solution

Identify the metals and their position in the activity series

We need to analyze the activity series of metals and find out where aluminum (Al), potassium (K), and silver (Ag) are placed. A widely used activity series can be viewed at the following link: https://en.wikipedia.org/wiki/Reactivity_series In the activity series, Al is placed higher than both K and Ag. The order is as follows: Al > K > Ag

Analyze the reaction with aqueous KCl

When a piece of aluminum metal is placed in aqueous \(\mathrm{KCl}\), we need to consider if aluminum can displace potassium in this solution. Since aluminum is less reactive than potassium (Al < K), it will not be able to displace potassium in the reaction. Therefore, no chemical reaction will occur in this instance.

Analyze the reaction with aqueous AgNO3

When a piece of aluminum metal is placed in aqueous \(\mathrm{AgNO}_{3}\), we need to consider if aluminum can displace silver in this solution. Since aluminum is more reactive than silver (Al > Ag), it will displace silver in the reaction. Therefore, a chemical reaction will occur in this instance, which can be represented by the following equation: \(2 \mathrm{Al} + 3 \mathrm{AgNO}_3 \rightarrow 2 \mathrm{Al(NO}_3)_3 + 3 \mathrm{Ag}\) The aluminum reacts with silver nitrate, forming aluminum nitrate and silver metal. In conclusion, when a piece of aluminum metal is placed in aqueous \(\mathrm{KCl}\), no chemical reaction occurs. However, when aluminum is placed in an aqueous \(\mathrm{AgNO}_{3}\) solution, a chemical reaction takes place due to the relative reactivity of the metals in the activity series.

Key concepts

Chemical Reactivity

Chemical reactivity refers to the tendency of a substance to engage in chemical reactions. It determines how easily a material can undergo a chemical change to form a new substance. Elements, particularly metals, have different levels of reactivity depending on their electron configurations. Metals that are more reactive readily lose their outer electrons to form positive ions or participate in reactions. For example, in the context of our exercise, when a piece of aluminum metal is placed in aqueous silver nitrate (\(\mathrm{AgNO}_{3}\)), the aluminum, being more reactive, displaces the silver due to its willingness to lose electrons more readily.

Understanding the reactivity of metals helps predict whether or not a chemical reaction will occur. In aqueous solutions, reactive metals can displace less reactive metals from their compounds, leading to a displacement reaction. This behavior is crucial in various applications, from metallurgic processes to the production of certain chemicals. For students grappling with chemistry homework, recognizing the implications of chemical reactivity can demystify why certain reactions occur while others don't.

Displacement Reactions

Displacement reactions are a type of chemical reaction where a more reactive element displaces a less reactive element from its compound. This takes place because the more reactive element has a more significant tendency to lose or gain electrons compared to the less reactive one. When analyzing such reactions, it's essential to consider the reactivity of the metals involved.

In the exercise example, the process involves aluminum placed in aqueous solutions of \(\mathrm{KCl}\) and \(\mathrm{AgNO}_{3}\). Because of aluminum's higher position in the reactivity series over silver, it can displace silver from \(\mathrm{AgNO}_{3}\) to form aluminum nitrate and free silver metal. In contrast, potassium is more reactive than aluminum, which is why aluminum cannot displace potassium from \(\mathrm{KCl}\). Such knowledge not only helps in predicting the outcomes of chemical reactions but also in the extraction and refining of metals from their ores.

Reactivity Series

The reactivity series is a ranking of metals based on their reactivity. This series predicts how metals will react with other substances like water, acid, and aqueous solutions. A higher position in the series indicates a metal that is more likely to lose electrons and react. In education, specifically chemistry homework, grasping the reactivity series is pivotal in solving problems related to displacement reactions and predicting the course of other chemical processes.

In the exercise provided, the series correctly forecasts that aluminum can displace silver from \(\mathrm{AgNO}_{3}\) since aluminum is above silver in the reactivity series. On the other hand, no reaction occurs between aluminum and \(\mathrm{KCl}\) because potassium stands higher than aluminum in the series. The use of the reactivity series as a tool for prediction emphasizes the methodology behind chemical reactions, aiding students in understanding the 'why' as well as the 'how' of chemical behavior.