Percent Of Oxygen In Potassium Chlorate Lab Answers

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

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 provides valuable hands-on experience in stoichiometry, gas law calculations, and experimental technique. Understanding the process and potential sources of error are crucial for accurate results. This article will provide a detailed breakdown of the experiment, including the procedure, calculations, potential sources of error, and safety precautions.

Understanding the Chemistry Behind the Experiment

The decomposition of potassium chlorate is represented by the following balanced chemical equation:

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 calculating the percentage of oxygen in the compound. 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 that was released.

Experimental Procedure: A Step-by-Step Guide

Materials:

• Potassium chlorate (KClO₃)
• Test tube
• Test tube holder
• Bunsen burner
• Ring stand
• Wire gauze
• Electronic balance
• Delivery tube
• Erlenmeyer flask or other suitable gas collection container
• Water
• Graduated cylinder

Procedure:

1. Weighing the Potassium Chlorate: Carefully weigh an empty, dry test tube using an electronic balance. Record this mass (m₁). Add approximately 2-3 grams of potassium chlorate to the test tube and record the total mass (m₂). The difference (m₂ - m₁) represents the mass of potassium chlorate used.

2. Setting up the Apparatus: Assemble the apparatus as shown in a typical laboratory manual. The test tube containing potassium chlorate should be securely clamped to the ring stand. The delivery tube should be securely fitted into the test tube and submerged in a flask or beaker filled with water. This will collect the oxygen gas produced.

3. Heating the Potassium Chlorate: Gently heat the test tube using a Bunsen burner, making sure to heat the entire length of the test tube evenly to avoid localized overheating. Continue heating until no further bubbling is observed. This indicates that the decomposition is complete. Let the test tube cool completely to room temperature.

4. Weighing the Potassium Chloride: After the test tube has cooled completely, carefully remove it from the apparatus and weigh it again using the electronic balance. Record this mass (m₃). The difference between (m₂ - m₃) represents the mass of oxygen gas evolved.

5. Calculating the Volume of Oxygen: Carefully measure the volume of water displaced in the collection flask. This volume represents the volume of oxygen gas produced. Note the temperature and atmospheric pressure of the laboratory.

6. Data Analysis and Calculations: The calculations involved are described in the next section.

Calculations and Data Analysis

The percentage of oxygen in potassium chlorate can be calculated using the following steps:

1. Mass of Oxygen: Calculate the mass of oxygen produced by subtracting the mass of the remaining potassium chloride (m₃) from the initial mass of potassium chlorate (m₂):

   Mass of Oxygen = m₂ - m₃

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

   Percentage of Oxygen = [(Mass of Oxygen / Mass of Potassium Chlorate) x 100]%

   Where:

   • Mass of Potassium Chlorate = m₂ - m₁

3. Molar Mass Calculations (Optional): A more rigorous calculation can be performed using the ideal gas law (PV = nRT) to determine the number of moles of oxygen gas produced. Knowing the number of moles of oxygen and the initial mass of potassium chlorate allows for a calculation based on the molar ratio in the balanced equation.

4. Theoretical vs. Experimental Values: Compare your experimentally determined percentage of oxygen with the theoretical value calculated using the molar masses of potassium, chlorine, and oxygen. This comparison helps evaluate the accuracy of your experimental technique.

Potential Sources of Error

Several factors can affect the accuracy of the experimental results. These include:

• Incomplete Decomposition: If the potassium chlorate is not heated sufficiently, the decomposition will be incomplete, leading to an underestimation of the percentage of oxygen.

• Loss of Oxygen: Some oxygen gas might escape from the apparatus before it can be collected, leading to an underestimation of the percentage of oxygen.

• Presence of Impurities: If the potassium chlorate sample contains impurities, this will affect the mass measurements and lead to inaccurate results.

• Measuring Errors: Errors in weighing the potassium chlorate and potassium chloride, or in measuring the volume of oxygen gas, will propagate through the calculations.

• Atmospheric Pressure: Variations in atmospheric pressure will affect the volume of oxygen collected and should be taken into account when using the ideal gas law.

Safety Precautions

• Always wear safety goggles: This is crucial to protect your eyes from any potential splashes or spills.

• Use a fume hood: The decomposition of potassium chlorate can produce small amounts of toxic fumes. Performing the experiment in a fume hood will minimize the risk of inhaling these fumes.

• Handle chemicals carefully: Avoid direct contact with potassium chlorate. If contact occurs, wash the affected area immediately with water.

• Heat carefully and avoid overheating: Overheating can lead to the rapid release of oxygen, potentially causing a violent reaction.

• Proper disposal: Dispose of all chemical waste according to your laboratory's guidelines.

Improving Experimental Accuracy

Several techniques can be employed to improve the accuracy of the experiment:

• Using a catalyst: Manganese(IV) oxide (MnO₂) can be added as a catalyst to speed up the decomposition reaction and ensure complete decomposition at lower temperatures, reducing the chance of oxygen loss.

• Precise measurements: Use an analytical balance for more accurate mass measurements and a gas buret for more accurate volume measurements.

• Temperature and pressure control: Measure the temperature and atmospheric pressure accurately and use these values in calculations.

Conclusion

The determination of the percentage of oxygen in potassium chlorate is a fundamental experiment in introductory chemistry. Understanding the procedure, calculations, potential sources of error, and safety precautions are essential for obtaining accurate and reliable results. Careful attention to detail and meticulous experimental technique are crucial for minimizing errors and achieving a result that closely aligns with the theoretical value. By carefully following this guide and addressing potential sources of error, students can gain a valuable understanding of stoichiometry, gas laws, and experimental design. This experiment highlights the importance of precise measurements and the careful interpretation of experimental data in chemistry. The discrepancy between theoretical and experimental values provides a valuable learning opportunity to analyze potential sources of error and refine experimental procedures for improved accuracy.