Percent Of Oxygen In Potassium Chlorate Lab Answers

Determining the Percentage of Oxygen in Potassium Chlorate: A Comprehensive Lab Report

The decomposition of potassium chlorate (KClO₃) into potassium chloride (KCl) and oxygen gas (O₂) is a classic chemistry experiment used to determine the percentage of oxygen by mass in the compound. This experiment allows students to apply stoichiometry, handle laboratory equipment safely, and analyze experimental data to calculate a crucial chemical property. This detailed guide will walk you through the experiment, explain the calculations involved, and offer insights into potential sources of error and improvements for accuracy.

Understanding the Reaction

The decomposition of potassium chlorate is a thermal decomposition reaction, meaning it requires heat to proceed. The balanced chemical equation is:

2KClO₃(s) → 2KCl(s) + 3O₂(g)

This equation tells us that for every 2 moles of potassium chlorate that decompose, 3 moles of oxygen gas are produced. This molar ratio is crucial for our calculations. The experiment involves heating a known mass of potassium chlorate until it completely decomposes. The mass of the remaining potassium chloride is then measured, allowing us to determine the mass of oxygen lost.

Materials and Procedure

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

• Potassium chlorate (KClO₃): Handle with care; avoid inhalation or skin contact.
• Test tube: Heat-resistant glass is essential.
• Test tube holder: For safe handling of the hot test tube.
• Bunsen burner: A heat source for the decomposition reaction.
• Ring stand and clamp: To securely hold the test tube above the Bunsen burner.
• Electronic balance: For precise mass measurements.
• Delivery tube: To direct the evolved oxygen gas (optional, but recommended for safety).
• Pneumatic trough: To collect the oxygen gas (optional, demonstrating gas law properties).
• Heat resistant mat: Protects the work surface from the heat of the Bunsen burner.
• Safety goggles: Essential for eye protection.

Procedure:

1. Weighing the Potassium Chlorate: Carefully weigh an empty, dry test tube using the electronic balance. Record the mass accurately. Then add approximately 2-3 grams of potassium chlorate to the test tube and re-weigh it. Record the mass of the potassium chlorate.

2. Setting up the Apparatus: Securely clamp the test tube containing the potassium chlorate to the ring stand. If using a delivery tube and pneumatic trough, assemble the apparatus to safely collect the oxygen gas. Ensure the tube is securely connected to prevent gas leakage.

3. Heating the Potassium Chlorate: Carefully heat the test tube using the Bunsen burner, applying heat gently at first to avoid splattering. Continue heating, gently swirling the test tube to ensure even heating. The potassium chlorate will melt and then decompose, producing oxygen gas (visible bubbling).

4. Continued Heating: Continue heating until the bubbling ceases, indicating complete decomposition. Make sure to heat the entire length of the test tube to ensure all of the potassium chlorate is decomposed.

5. Cooling and Weighing: Allow the test tube to cool completely to room temperature before weighing it again. Record this final mass.

6. Calculations: Use the initial and final masses to determine the mass of oxygen lost and calculate the percentage of oxygen in the potassium chlorate sample.

Calculations and Data Analysis

The key to accurately determining the percentage of oxygen lies in careful mass measurements and correct stoichiometric calculations.

1. Mass of Oxygen Lost: Subtract the final mass of the test tube and potassium chloride from the initial mass of the test tube and potassium chlorate. This difference represents the mass of oxygen gas produced.

2. Moles of Oxygen: Convert the mass of oxygen lost to moles using the molar mass of oxygen (32.00 g/mol).

3. Moles of Potassium Chlorate: Use the balanced chemical equation (2KClO₃ → 2KCl + 3O₂) to determine the moles of potassium chlorate that decomposed. The molar ratio of KClO₃ to O₂ is 2:3.

4. Mass of Potassium Chlorate: Convert the moles of potassium chlorate to grams using its molar mass (122.55 g/mol).

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

(Mass of Oxygen / Mass of Potassium Chlorate) x 100%

Example:

Let's say the initial mass of the test tube + KClO₃ was 25.00 g, and the final mass of the test tube + KCl was 23.00 g. The mass of oxygen lost is 2.00 g.

• Moles of Oxygen = 2.00 g / 32.00 g/mol = 0.0625 mol
• Moles of KClO₃ = (2/3) x 0.0625 mol = 0.0417 mol
• Mass of KClO₃ = 0.0417 mol x 122.55 g/mol = 5.11 g
• Percentage of Oxygen = (2.00 g / 5.11 g) x 100% = 39.1%

This calculated percentage can then be compared to the theoretical percentage of oxygen in potassium chlorate (approximately 39.2%).

Sources of Error and Improvements

Several factors can contribute to errors in the experimental results:

• Incomplete Decomposition: If the potassium chlorate is not heated sufficiently, some may remain undecomposed, leading to an underestimation of the oxygen percentage.

• Loss of Product: Some potassium chloride might be lost during the experiment due to splattering or incomplete collection. This also causes an underestimation of oxygen percentage.

• Impurities in KClO₃: The presence of impurities in the potassium chlorate sample can affect the results.

• Air Bubbles in Measurement: If collecting oxygen over water, the presence of dissolved air in the water can slightly increase the measured volume.

• Improper Calibration: Ensure the balance is properly calibrated to ensure accurate mass measurements.

To improve accuracy:

• Careful heating: Use a gentle and consistent heating technique to ensure complete decomposition without loss of product.

• Multiple trials: Perform multiple trials and calculate the average percentage of oxygen to minimize the impact of random errors.

• High-purity reactants: Use high-purity potassium chlorate to minimize the influence of impurities.

• Proper technique: Use correct techniques in handling glassware and chemicals to ensure no losses occur.

• Data analysis: Carefully analyze your data, identify any outliers, and calculate averages to minimize systematic errors.

Conclusion

The decomposition of potassium chlorate provides a valuable hands-on learning experience in stoichiometry and experimental techniques. While sources of error are inevitable, careful attention to detail, proper techniques, and multiple trials can significantly improve the accuracy of the determined percentage of oxygen. Comparing the experimental result to the theoretical value allows for assessment of experimental error and understanding of its sources. This process highlights the importance of precise measurements, meticulous procedure, and thoughtful data analysis in quantitative chemical experiments. Remember always to prioritize safety and follow appropriate laboratory procedures.