Percent Of Oxygen In Potassium Chlorate Lab Answers

Determining the Percentage of Oxygen in Potassium Chlorate: A Comprehensive Guide

Determining the percentage of oxygen in potassium chlorate (KClO₃) is a common experiment in introductory chemistry labs. This experiment allows students to practice fundamental lab techniques like heating, weighing, and data analysis, while also reinforcing their understanding of stoichiometry and the properties of chemical compounds. This article provides a detailed walkthrough of the experiment, including the procedure, scientific explanation, potential sources of error, and frequently asked questions. Understanding the percentage of oxygen in potassium chlorate is crucial for various applications, from understanding its decomposition reaction to its use in different chemical processes.

Introduction

Potassium chlorate (KClO₃) is an inorganic compound that decomposes upon heating, releasing oxygen gas (O₂) and leaving behind potassium chloride (KCl) as a solid residue. This decomposition reaction is represented by the following balanced chemical equation:

2KClO₃(s) → 2KCl(s) + 3O₂(g)

The aim of this experiment is to determine the percentage by mass of oxygen in potassium chlorate by measuring the mass of oxygen gas released during the decomposition. This allows us to experimentally verify the theoretical percentage calculated from the molar masses of the elements involved. Understanding this percentage is vital for stoichiometric calculations and other chemical analyses involving potassium chlorate.

Materials and Equipment

To conduct this experiment, you will need the following materials and equipment:

• Potassium chlorate (KClO₃)
• Test tube
• Test tube holder
• Bunsen burner
• Heat resistant mat
• Analytical balance
• Spatula
• Goggles
• Gloves
• Weighing boat or small beaker

Procedure

Follow these steps carefully to perform the experiment:

1. Weighing the Test Tube: Carefully weigh an empty, clean, and dry test tube using an analytical balance. Record the mass in grams with as much precision as possible. Let's call this mass m₁.

2. Adding Potassium Chlorate: Using a clean, dry spatula, add approximately 1-2 grams of potassium chlorate to the test tube. Avoid touching the potassium chlorate with your bare hands; use the spatula. Record the mass of the test tube plus the potassium chlorate. Let's call this mass m₂. The difference (m₂ - m₁) is the mass of potassium chlorate used.

3. Heating the Potassium Chlorate: Using a test tube holder, carefully heat the test tube containing the potassium chlorate using a Bunsen burner. Heat gently at first, then increase the heat as the potassium chlorate begins to decompose. You will observe the release of oxygen gas and a change in the appearance of the solid. Continue heating until no further change is observed – this indicates complete decomposition. Be cautious during this step; avoid pointing the test tube towards yourself or anyone else.

4. Cooling and Weighing: Allow the test tube to cool completely to room temperature before weighing it again. This is crucial to prevent errors due to thermal expansion or convection currents affecting the balance reading. Record the mass of the test tube and the remaining potassium chloride. Let's call this mass m₃.

Data Analysis and Calculations

1. Mass of Oxygen Released: Calculate the mass of oxygen released during the decomposition by subtracting the mass of the test tube and potassium chloride (m₃) from the mass of the test tube and potassium chlorate (m₂). This is represented by: m₂ - m₃ = mass of O₂.

2. Percentage of Oxygen: Calculate the percentage of oxygen in the potassium chlorate sample using the following formula:

   (Mass of O₂ / Mass of KClO₃) x 100% = Percentage of Oxygen

   Where:

   • Mass of O₂ is the mass of oxygen calculated in step 1.
   • Mass of KClO₃ is the initial mass of potassium chlorate (m₂ - m₁).

Scientific Explanation

The experiment relies on the principle of conservation of mass. The mass of the reactants (potassium chlorate) equals the mass of the products (potassium chloride and oxygen). By measuring the mass difference before and after heating, we directly determine the mass of oxygen released. The theoretical percentage of oxygen in potassium chlorate can be calculated using the molar masses of the elements:

• Molar mass of K = 39.10 g/mol
• Molar mass of Cl = 35.45 g/mol
• Molar mass of O = 16.00 g/mol

Molar mass of KClO₃ = 39.10 + 35.45 + (3 × 16.00) = 122.55 g/mol

Mass of oxygen in 1 mole of KClO₃ = (3 × 16.00) = 48.00 g

Theoretical percentage of oxygen = (48.00 g / 122.55 g) x 100% ≈ 39.17%

The experimental percentage obtained should be close to the theoretical value. Any significant deviation indicates potential errors in the procedure or the presence of impurities in the potassium chlorate sample.

Sources of Error

Several factors can contribute to errors in the experimental determination of the percentage of oxygen:

• Incomplete Decomposition: If the potassium chlorate is not heated sufficiently, some of it may remain undecomposed, leading to an underestimation of the oxygen released.
• Loss of Sample: Some potassium chlorate may be lost during handling or transfer, affecting the accuracy of the mass measurements.
• Impurities: Impurities in the potassium chlorate sample can alter the mass measurements and lead to inaccurate results.
• Incomplete Cooling: Weighing the test tube before it has cooled completely can lead to errors due to thermal expansion.
• Balance Calibration: An improperly calibrated analytical balance will result in inaccurate mass readings.

Frequently Asked Questions (FAQ)

Q: Why is it important to heat the test tube gently at first?

A: Gently heating prevents the rapid release of oxygen, which can cause the sample to splatter or even explode, leading to inaccurate results and potential safety hazards.

Q: What precautions should be taken during the heating process?

A: Always wear safety goggles and gloves to protect your eyes and hands. Never point the test tube towards yourself or anyone else while heating. Use a heat-resistant mat to protect the surface beneath the burner.

Q: What if my experimental result differs significantly from the theoretical value?

A: Significant deviations suggest potential errors in the procedure. Carefully review your steps, checking for incomplete decomposition, sample loss, impurities, or inaccurate weighing. Repeating the experiment with greater care can improve the accuracy.

Q: Can this experiment be modified to determine the percentage of other elements in potassium chlorate?

A: No, not directly. This method only determines the mass of oxygen lost during decomposition. To determine the percentage of potassium or chlorine, different analytical techniques, such as titration or spectroscopy, would be required.

Conclusion

Determining the percentage of oxygen in potassium chlorate is a valuable experiment for reinforcing fundamental chemistry concepts and practical laboratory skills. By carefully following the procedure and analyzing the data, students can experimentally verify the theoretical percentage of oxygen in potassium chlorate and gain a deeper understanding of stoichiometry, chemical reactions, and the importance of precise measurements in scientific investigations. Understanding potential sources of error and taking appropriate precautions ensures accurate and reliable results. Remember that consistent and careful experimental work is essential for obtaining results that closely match the theoretical value. Through this process, students develop valuable critical thinking skills and enhance their understanding of the scientific method.