Question

A common experiment in introductory chemistry courses involves heating a weighed mixture of potassium chlorate, \(\mathrm{KClO}_{3}\), and potassium chloride. Potassium chlorate decomposes when heated, producing potassium chloride and evolving oxygen gas. By measuring the volume of oxygen gas produced in this experiment, students can calculate the relative percentage of \(\mathrm{KClO}_{3}\) and \(\mathrm{KCl}\) in the original mixture. Write the balanced chemical equation for this process.

Short answer

The balanced chemical equation for the decomposition of potassium chlorate (KClO₃) upon heating is: \[ 2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2 \]

Step-by-step solution

Identify the Reactants and Products

The first step in writing a balanced chemical equation is to list down the reactants and products involved. In this case, we have: Reactants: 1. Potassium chlorate (KClO₃) Products: 1. Potassium chloride (KCl) 2. Oxygen gas (O₂)

Writing the Unbalanced Chemical Equation

Now, write the unbalanced chemical equation: \[ \mathrm{KClO}_3 \rightarrow \mathrm{KCl} + \mathrm{O}_2 \]

Balancing the Chemical Equation

Next, we need to balance the chemical equation, which means that there must be equal numbers of each type of atom on both sides of the reaction. First, look at the oxygen atoms, there are 3 oxygen atoms in \(\mathrm{KClO}_3\) but only 2 oxygen atoms in \(\mathrm{O}_2\). To balance the oxygen, we need to have a common multiple of 3 and 2, which is 6. That means we need 2 \(\mathrm{KClO}_3\) and 3 \(\mathrm{O}_2\) to balance the oxygen atoms: \[ 2\mathrm{KClO}_3 \rightarrow \mathrm{KCl} + 3\mathrm{O}_2 \] Now the oxygen atoms are balanced, but we have an imbalance in the number of potassium (K) and chloride (Cl) atoms. On the reactant side, there are 2 K and 2 Cl atoms, so we need to adjust the products to have 2 KCl: \[ 2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2 \]

Final Balanced Chemical Equation

Now that the chemical equation is balanced, you can simply write the final balanced equation as follows: \[ 2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2 \] This balanced equation indicates that when 2 moles of potassium chlorate (KClO₃) decompose upon heating, they produce 2 moles of potassium chloride (KCl) and 3 moles of oxygen gas (O₂).

Key concepts

Potassium Chlorate Decomposition

Potassium chlorate (\(\mathrm{KClO}_3\)decomposes when heated, breaking down into two other substances: potassium chloride (\(\mathrm{KCl}\)and oxygen gas (\(\mathrm{O}_2\). This reaction is a classic example of a decomposition reaction, which is a type of chemical reaction where one compound breaks down into two or more simpler substances. In the case of potassium chlorate, heat acts as the catalyst that drives this transformation. The decomposition is both practical and illustrative: it’s commonly performed in educational labs to demonstrate chemical changes and gas evolution.
The balanced chemical equation for this reaction is written as follows:
\[2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2\]Understanding this equation helps in visualizing the molecular rearrangement whereby each formula unit of \(\mathrm{KClO}_3\) produces one formula unit of \(\mathrm{KCl}\) and 1.5 molecules of oxygen. However, practical balancing requires us to consider whole atoms, leading to two chlorate molecules decomposing to produce three oxygen molecules. This is critical in predicting the results of the reaction accurately.

Stoichiometry

Stoichiometry is a branch of chemistry focused on measuring the quantities of reactants and products in chemical reactions. It's essentially the math-based side of chemistry that relies on balanced equations. For the decomposition of potassium chlorate, stoichiometry allows us to know exactly how much \(\mathrm{KClO}_3\)is needed to produce a certain amount of oxygen gas. From the balanced equation:\[2\mathrm{KClO}_3 \rightarrow 2\mathrm{KCl} + 3\mathrm{O}_2\]We know that every 2 moles of potassium chlorate produces 3 moles of oxygen gas. This ratio is incredibly useful:

• For converting between moles of reactants and products,
• For scaling reactions up or down for different conditions,
• And for ensuring that chemical reactions go to completion using the calculated reactant ratios.

Stoichiometry also involves the concepts of limiting reactants and theoretical yields. In this reaction, fully understanding the stoichiometric ratios can enable prediction of the maximum amount of \(\mathrm{O}_2\)that can be formed during the reaction.

Oxygen Gas Production

The production of oxygen gas in the decomposition of potassium chlorate is one of the most visually engaging aspects of this reaction. When heated, the breakdown of \(\mathrm{KClO}_3\)leads to the release of oxygen, which can be measured as part of lab experiments. Measuring the volume of oxygen produced gives students a practical way to apply what they've learned about stoichiometry. It enables them to calculate the theoretical and actual yield of a reaction by comparing the measured amount to the amount predicted by stoichiometric calculations.
To measure oxygen:

• Students might use a gas syringe or collect it over water in a graduated cylinder,
• Temperature and pressure should be considered, since they can affect gas volume,
• Any deviations can lead to deeper analysis and discussion regarding experimental error and accuracy.

This step in the experiment exemplifies not just the application of mathematical principles but also a hands-on approach to understanding the production and capture of gases in chemistry.

Introductory Chemistry Lab Experiment

The decomposition of potassium chlorate is an excellent introductory chemistry lab experiment. It provides students with a hands-on experience in observing chemical reactions, learning about gas production, and applying stoichiometry calculations. This experiment encompasses many foundational chemistry principles, making it ideal for new students.
Key things students learn include:

• How to properly heat a substance to initiate a reaction,
• The importance of careful measurement and observation in the lab,
• The practice of safely capturing and measuring gas production, and
• Interpreting results to understand both chemical processes and reaction efficiencies.

Through this experiment, students build a fundamental understanding of basic lab techniques and equipment. Engaging in this type of activity fosters a deeper interest in chemistry by connecting theoretical learning with tactile experimentation.