Experiment 10 Composition Of Potassium Chlorate

Experiment 10: Unveiling the Composition of Potassium Chlorate

Potassium chlorate, a versatile chemical compound with the formula KClO3, holds a significant place in the realm of chemistry due to its oxidizing properties. Experiment 10 delves into the quantitative analysis of potassium chlorate, aiming to determine its elemental composition through controlled thermal decomposition. This experiment not only reinforces fundamental chemical principles but also provides hands-on experience in precise measurement and data analysis.

Introduction

Quantitative analysis plays a pivotal role in understanding the composition of chemical compounds. By carefully measuring the masses of reactants and products involved in a chemical reaction, we can determine the percentage composition of each element within the compound. In Experiment 10, we focus on potassium chlorate (KClO3), a crystalline solid that decomposes upon heating to produce potassium chloride (KCl) and oxygen gas (O2).

The balanced chemical equation for the decomposition reaction is:

2 KClO3(s) → 2 KCl(s) + 3 O2(g)

This experiment leverages the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. By accurately measuring the mass of potassium chlorate before heating and the mass of potassium chloride after the reaction, we can calculate the mass of oxygen released. This data allows us to determine the percentage composition of potassium chlorate.

Objectives

The primary objectives of Experiment 10 are:

• To quantitatively decompose potassium chlorate into potassium chloride and oxygen gas.
• To accurately measure the mass of potassium chlorate before and after decomposition.
• To calculate the mass of oxygen produced during the reaction.
• To determine the percentage composition of potassium, chlorine, and oxygen in potassium chlorate.
• To compare the experimental results with the theoretical composition of potassium chlorate.
• To understand the principles of stoichiometry and its application in quantitative analysis.
• To enhance laboratory skills in handling chemicals, operating equipment, and collecting data.

Materials and Equipment

To conduct Experiment 10 effectively, the following materials and equipment are required:

• Potassium chlorate (KClO3): A pure sample of potassium chlorate is essential for accurate results.
• Manganese dioxide (MnO2): Used as a catalyst to speed up the decomposition of potassium chlorate.
• Test tube: A heat-resistant test tube is used to hold the potassium chlorate during heating.
• Test tube holder: Used to safely hold the test tube while heating.
• Bunsen burner: Provides a controlled heat source for the decomposition reaction.
• Clay triangle: Supports the test tube on the ring stand.
• Ring stand: Provides a stable support for the clay triangle and test tube.
• Balance: A high-precision balance is crucial for accurate mass measurements (0.001g precision).
• Spatula: Used to transfer and measure the potassium chlorate and manganese dioxide.
• Weighing paper: Used to accurately weigh the chemicals on the balance.
• Safety goggles: Essential for eye protection during the experiment.
• Heat-resistant gloves: To protect hands from burns when handling hot equipment.

Safety Precautions

Working with chemicals and high temperatures necessitates strict adherence to safety protocols. The following precautions must be observed during Experiment 10:

1. Eye Protection: Always wear safety goggles to protect your eyes from chemical splashes or fumes.
2. Hand Protection: Wear heat-resistant gloves when handling hot equipment or chemicals.
3. Chemical Handling: Handle potassium chlorate and manganese dioxide with care, avoiding skin contact or inhalation.
4. Heating: Use a controlled flame and avoid overheating the test tube to prevent explosions.
5. Ventilation: Conduct the experiment in a well-ventilated area to avoid inhaling fumes.
6. Waste Disposal: Dispose of chemical waste properly according to laboratory guidelines.
7. Emergency Procedures: Familiarize yourself with the location of safety equipment, such as eyewash stations and fire extinguishers.

Procedure

The procedure for Experiment 10 involves several key steps, each requiring precision and attention to detail:

1. Preparation:
   • Clean and dry the test tube thoroughly.
   • Weigh the empty test tube using the balance and record the mass (Mass of empty test tube).
2. Mixing Reactants:
   • Accurately weigh approximately 2-3 grams of potassium chlorate on weighing paper. Record the exact mass (Mass of KClO3).
   • Add a small amount of manganese dioxide (approximately 0.1-0.2 grams) to the potassium chlorate in the test tube. The manganese dioxide acts as a catalyst.
   • Gently mix the potassium chlorate and manganese dioxide in the test tube.
3. Heating:
   • Secure the test tube in the test tube holder.
   • Position the test tube in the clay triangle on the ring stand.
   • Light the Bunsen burner and adjust the flame to a moderate heat.
   • Begin heating the test tube gently, focusing the flame on the lower portion of the tube.
   • Observe the reaction carefully. The potassium chlorate will melt and begin to decompose, releasing oxygen gas.
   • Continue heating until the reaction is complete, indicated by the cessation of oxygen gas evolution. The mixture will solidify into potassium chloride.
   • Allow the test tube to cool completely to room temperature.
4. Weighing After Decomposition:
   • Once the test tube has cooled, weigh it again using the balance and record the mass (Mass of test tube + KCl).
5. Calculations:
   • Calculate the mass of potassium chloride (KCl) produced:
     • Mass of KCl = (Mass of test tube + KCl) - (Mass of empty test tube)
   • Calculate the mass of oxygen (O2) released:
     • Mass of O2 = (Mass of KClO3 + Mass of empty test tube) - (Mass of test tube + KCl)
   • Calculate the percentage composition of potassium (K), chlorine (Cl), and oxygen (O) in potassium chlorate:
     • Determine the molar mass of KClO3, KCl, and O2.
     • Calculate the moles of KClO3 decomposed.
     • Calculate the moles of KCl produced and O2 released based on the stoichiometry of the reaction.
     • Calculate the mass of K, Cl, and O in the original sample of KClO3.
     • Calculate the percentage composition of each element:
       • %K = (Mass of K / Mass of KClO3) * 100
       • %Cl = (Mass of Cl / Mass of KClO3) * 100
       • %O = (Mass of O / Mass of KClO3) * 100
6. Data Analysis:
   • Compare the experimental percentage composition with the theoretical percentage composition of potassium chlorate.
   • Calculate the percentage error for each element.
   • Analyze potential sources of error and their impact on the results.

Detailed Steps with Explanations

To ensure a successful and accurate Experiment 10, let's delve into each step with more detailed explanations:

1. Preparation:

   • Cleaning the Test Tube: A clean test tube is crucial to avoid any contamination that could affect the mass measurements. Wash the test tube thoroughly with soap and water, rinse it with distilled water, and dry it completely before use.
   • Weighing the Empty Test Tube: Place the clean, dry test tube on the balance and record the mass to the nearest 0.001g. This mass will be used as a reference point for subsequent calculations. Make sure the balance is properly calibrated before taking any measurements.

2. Mixing Reactants:

   • Weighing Potassium Chlorate: Use a clean spatula to transfer approximately 2-3 grams of potassium chlorate onto a piece of weighing paper. Record the exact mass to the nearest 0.001g. Avoid spilling the potassium chlorate, and ensure the weighing paper is clean and dry.
   • Adding Manganese Dioxide: Manganese dioxide (MnO2) acts as a catalyst, a substance that speeds up a chemical reaction without being consumed in the process. Add a small amount (0.1-0.2 grams) of MnO2 to the test tube containing the potassium chlorate. The MnO2 lowers the activation energy required for the decomposition of KClO3, making the reaction proceed more readily at a lower temperature.
   • Mixing Thoroughly: Gently mix the potassium chlorate and manganese dioxide using a clean stirring rod or by carefully swirling the test tube. Ensure that the two substances are well mixed to facilitate an even decomposition reaction.

3. Heating:

   • Setting Up the Apparatus: Secure the test tube in the test tube holder and position it in the clay triangle on the ring stand. The clay triangle provides a stable support for the test tube and allows for even heating.
   • Adjusting the Bunsen Burner: Light the Bunsen burner and adjust the flame to a moderate heat. A blue flame with a slight orange tint is ideal for heating the test tube. Avoid using a very hot flame, as this could cause the potassium chlorate to decompose too rapidly and potentially cause an explosion.
   • Heating the Test Tube: Begin heating the test tube gently, focusing the flame on the lower portion of the tube where the potassium chlorate mixture is located. Move the flame around to ensure even heating and prevent localized overheating.
   • Observing the Reaction: As the potassium chlorate heats up, it will begin to melt and decompose, releasing oxygen gas. You may observe bubbles forming and escaping from the mixture. Continue heating until the reaction is complete, indicated by the cessation of oxygen gas evolution. The mixture will solidify into potassium chloride, which will appear as a white or slightly grayish solid.
   • Cooling the Test Tube: Once the reaction is complete, turn off the Bunsen burner and allow the test tube to cool completely to room temperature. Avoid quenching the hot test tube with water, as this could cause it to crack or shatter.

4. Weighing After Decomposition:

   • Weighing the Test Tube and Potassium Chloride: After the test tube has cooled completely, weigh it again using the balance and record the mass to the nearest 0.001g. This mass represents the combined mass of the test tube and the potassium chloride that remains after the decomposition of the potassium chlorate.

5. Calculations:

   • Calculating the Mass of Potassium Chloride: Subtract the mass of the empty test tube from the mass of the test tube and potassium chloride to determine the mass of potassium chloride produced during the reaction.
     • Mass of KCl = (Mass of test tube + KCl) - (Mass of empty test tube)
   • Calculating the Mass of Oxygen: Subtract the mass of the test tube and potassium chloride from the initial mass of the test tube and potassium chlorate to determine the mass of oxygen released during the reaction.
     • Mass of O2 = (Mass of KClO3 + Mass of empty test tube) - (Mass of test tube + KCl)
   • Calculating the Percentage Composition:
     • Determine the molar mass of KClO3 (122.55 g/mol), KCl (74.55 g/mol), and O2 (32.00 g/mol).
     • Calculate the moles of KClO3 decomposed using the formula:
       • Moles of KClO3 = Mass of KClO3 / Molar mass of KClO3
     • Based on the balanced chemical equation (2 KClO3 → 2 KCl + 3 O2), calculate the moles of KCl produced and O2 released:
       • Moles of KCl = Moles of KClO3
       • Moles of O2 = (3/2) * Moles of KClO3
     • Calculate the mass of K, Cl, and O in the original sample of KClO3 using the molar masses and the stoichiometry of the reaction:
       • Mass of K = (Moles of KCl) * (Molar mass of K) = (Moles of KCl) * (39.10 g/mol)
       • Mass of Cl = (Moles of KCl) * (Molar mass of Cl) = (Moles of KCl) * (35.45 g/mol)
       • Mass of O = (Moles of O2) * (Molar mass of O2) = (Moles of O2) * (32.00 g/mol)
     • Calculate the percentage composition of each element:
       • %K = (Mass of K / Mass of KClO3) * 100
       • %Cl = (Mass of Cl / Mass of KClO3) * 100
       • %O = (Mass of O / Mass of KClO3) * 100

6. Data Analysis:

   • Comparing Experimental and Theoretical Values: Compare the experimental percentage composition values with the theoretical percentage composition values of potassium chlorate:
     • Theoretical %K = (39.10 g/mol / 122.55 g/mol) * 100 = 31.90%
     • Theoretical %Cl = (35.45 g/mol / 122.55 g/mol) * 100 = 28.93%
     • Theoretical %O = (48.00 g/mol / 122.55 g/mol) * 100 = 39.17%
   • Calculating Percentage Error: Calculate the percentage error for each element using the formula:
     • Percentage Error = |(Experimental Value - Theoretical Value) / Theoretical Value| * 100
   • Analyzing Sources of Error: Identify and analyze potential sources of error that could have affected the accuracy of the results. These errors could include:
     • Incomplete decomposition of potassium chlorate.
     • Loss of oxygen gas due to leaks in the apparatus.
     • Inaccurate mass measurements due to balance limitations or human error.
     • Impurities in the potassium chlorate or manganese dioxide.
     • Absorption of moisture from the air.

Expected Results and Discussion

The expected results of Experiment 10 should closely align with the theoretical composition of potassium chlorate. However, due to experimental errors, some deviation is inevitable. The percentage error for each element should be minimized through careful technique and precise measurements.

A successful experiment will demonstrate the following:

• Accurate measurement of the mass of potassium chlorate before and after decomposition.
• Effective decomposition of potassium chlorate into potassium chloride and oxygen gas.
• Calculation of the mass of oxygen released during the reaction.
• Determination of the percentage composition of potassium, chlorine, and oxygen in potassium chlorate.
• Comparison of the experimental results with the theoretical composition, with minimal percentage error.

Conclusion

Experiment 10 provides a hands-on experience in quantitative analysis, allowing students to determine the elemental composition of potassium chlorate through controlled thermal decomposition. By carefully measuring the masses of reactants and products, applying stoichiometric principles, and analyzing potential sources of error, students can gain a deeper understanding of chemical composition and the law of conservation of mass. This experiment reinforces fundamental chemical concepts and enhances laboratory skills, contributing to a more comprehensive understanding of chemistry.