Problem 34 - Chemistry in 30 days

Question

Which of the following gases is evolved when aluminum is boiled with caustic potash? (a) \(\mathrm{O}_{2}\) (b) Both \(\mathrm{O}_{2}\) and \(\mathrm{H}_{2}\) (c) \(\mathrm{H}_{2} \overline{\mathrm{O}}\) (vapour) (d) \(\mathrm{H}_{2}\) \(\mathrm{CO}\)

Step-by-Step Solution

Answer

The gas evolved is hydrogen (H_2).

Step 1: Understanding the Reaction

When aluminum (Al) reacts with caustic potash (KOH), it is an example of a reaction between a metal and a strong base. Aluminum reacts with potash to form potassium aluminate and hydrogen gas is evolved as a result of this reaction.

Step 2: Write the Chemical Equation

The reaction can be represented with the following chemical equation:\[ 2 ext{Al} + 2 ext{KOH} + 6 ext{H}_2 ext{O} ightarrow 2 ext{KAl(OH)}_4 + 3 ext{H}_2 \]This equation shows that hydrogen gas (H_2) is evolved during the reaction.

Step 3: Analyzing the Evolved Gas

From the chemical equation, and understanding the process taking place, the gas evolved is hydrogen (H_2). Oxygen and water vapor are not free gases in this case, and carbon monoxide was not present in the reaction equation. Thus, the correct answer can be concluded from the available options.

Key Concepts

Hydrogen Gas Evolution

When aluminum reacts with caustic potash, hydrogen gas is produced. This type of reaction is an example of a metal reacting with a strong base. The evolution of hydrogen gas is a common occurrence in such reactions because metals can easily donate electrons to hydrogen ions present in the base to form hydrogen gas. Hydrogen is a diatomic molecule ( H_2 ), meaning it consists of two hydrogen atoms bonded together. Hydrogen gas lacks color, taste, and odor. It is highly flammable and forms explosive mixtures with air. This is why observing precautions while conducting such reactions is important. In laboratory settings, evolved hydrogen is often collected for experimental purposes, but always handled with care to avoid accidents.

Aluminum and Caustic Potash Reaction

The reaction between aluminum and caustic potash is significant for chemistry learners as it demonstrates the interaction between a reactive metal and a strong base. Aluminum is a common metal used in many applications due to its lightweight and durable nature. Caustic potash, known chemically as potassium hydroxide (KOH), is a powerful alkali used in diverse chemical processes. When aluminum and potassium hydroxide react, they produce potassium aluminate and hydrogen gas. This process is described by the balanced chemical equation: \[2 \text{Al} + 2 \text{KOH} + 6 \text{H}_2\text{O} \rightarrow 2 \text{KAl(OH)}_4 + 3 \text{H}_2\].
Aluminum undergoes oxidation by donating electrons, while the hydroxide ions from caustic potash facilitate the generation of water molecules and hydrogen gas. It's an interesting reaction that allows students to explore how metals can behave in basic solutions.

Chemical Equation

Chemical equations are essential tools for understanding chemical reactions. They provide a concise way to depict how reactants are transformed into products. Each side of the equation must be balanced, indicating that the number of atoms for each element remains equal before and after the reaction. Balancing equations ensures that we adhere to the law of conservation of mass.
In the case of the reaction between aluminum and caustic potash, the chemical equation:\[2 \text{Al} + 2 \text{KOH} + 6 \text{H}_2\text{O} \rightarrow 2 \text{KAl(OH)}_4 + 3 \text{H}_2\] illustrates this balance effectively. It shows that two aluminum atoms, two potassium hydroxide molecules, and six water molecules are converted into two potassium aluminate molecules and three hydrogen molecules. Being able to read and write chemical equations empowers us to understand what substances are involved, how they interact, and what they yield during a chemical process.