Report For Experiment 10 Composition Of Potassium Chlorate

Experiment 10: Composition of Potassium Chlorate

Chemical reactions can often be represented using balanced chemical equations. These equations provide quantitative information regarding the number of moles of each reactant that will react and the number of moles of each product that will be produced. In order to confirm these quantitative relationships, it is necessary to determine the mass of reactants used and the mass of products formed. This experiment is designed to provide you with experience in obtaining data of this type and in using the data to confirm the quantitative relationships inherent in a balanced chemical equation.

Introduction

Potassium chlorate (KClO3) is a crystalline solid that decomposes when heated, producing oxygen gas and potassium chloride (KCl). The balanced equation for this reaction is:

2 KClO3(s) → 2 KCl(s) + 3 O2(g)

This reaction follows the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants (KClO3) must equal the total mass of the products (KCl and O2). By carefully measuring the mass of KClO3 before heating and the mass of KCl after heating, we can determine the mass of O2 produced and verify the stoichiometry of the reaction.

Objectives

The objectives of this experiment are:

• To experimentally determine the mass of oxygen produced by the decomposition of a known mass of potassium chlorate.
• To calculate the theoretical mass of oxygen that should be produced based on the balanced chemical equation.
• To compare the experimental and theoretical values and calculate the percent error.
• To reinforce understanding of stoichiometry, the law of conservation of mass, and the relationship between mass, moles, and molar mass.

Materials

• Potassium chlorate (KClO3)
• Manganese dioxide (MnO2) (catalyst)
• Test tube
• Test tube clamp
• Bunsen burner
• Balance
• Clay triangle
• Ring stand
• Evaporating dish
• Spatula

Procedure

1. Preparation:
   • Clean and dry a test tube.
   • Weigh the clean, dry test tube accurately using an analytical balance and record the mass.
2. Mixing Reactants:
   • Carefully weigh approximately 2-3 grams of potassium chlorate (KClO3) into the test tube. Record the exact mass.
   • Add a small amount of manganese dioxide (MnO2) to the test tube. MnO2 acts as a catalyst to speed up the decomposition of KClO3.
   • Mix the contents of the test tube by gently swirling the tube.
3. Heating:
   • Clamp the test tube to a ring stand at an angle, ensuring the mouth of the tube is pointing away from yourself and others.
   • Heat the test tube gently with a Bunsen burner. Move the flame along the length of the test tube to ensure even heating and prevent the KClO3 from melting and solidifying at the bottom.
   • Continue heating until no more oxygen gas is evolved. You can test for oxygen evolution by inserting a glowing splint into the mouth of the test tube. If oxygen is present, the splint will re-ignite.
4. Cooling and Weighing:
   • Allow the test tube to cool to room temperature.
   • Weigh the test tube and its contents (potassium chloride and manganese dioxide) accurately using the same analytical balance. Record the mass.
5. Calculations:
   • Calculate the mass of oxygen produced by subtracting the mass of the test tube and its contents after heating from the mass of the test tube and potassium chlorate before heating.
   • Calculate the theoretical mass of oxygen that should be produced based on the balanced chemical equation and the initial mass of potassium chlorate.
   • Calculate the percent error by comparing the experimental and theoretical values.
6. Repeat:
   • Repeat the experiment two more times to improve accuracy and precision.

Data and Observations

Record all measurements and observations in a data table, similar to the one below:

Calculations

1. Mass of KClO3: Subtract the mass of the test tube from the mass of the test tube + KClO3.

   Mass of KClO3 = (Mass of test tube + KClO3) - (Mass of test tube)

2. Mass of O2 produced (experimental): Subtract the mass of the test tube + KCl + MnO2 from the mass of the test tube + KClO3.

   Mass of O2 (experimental) = (Mass of test tube + KClO3) - (Mass of test tube + KCl + MnO2)

3. Moles of KClO3: Divide the mass of KClO3 by its molar mass (122.55 g/mol).

   Moles of KClO3 = (Mass of KClO3) / (Molar mass of KClO3)

4. Theoretical moles of O2: Use the stoichiometry of the balanced equation to determine the moles of O2 produced from the moles of KClO3. From the balanced equation, 2 moles of KClO3 produce 3 moles of O2.

   Theoretical moles of O2 = (Moles of KClO3) * (3 moles O2 / 2 moles KClO3)

5. Theoretical mass of O2: Multiply the theoretical moles of O2 by its molar mass (32.00 g/mol).

   Theoretical mass of O2 = (Theoretical moles of O2) * (Molar mass of O2)

6. Percent error: Calculate the percent error using the formula:

   Percent error = |(Experimental value - Theoretical value) / Theoretical value| * 100%

Expected Results and Discussion

The expected results of this experiment are that the experimental mass of oxygen produced will be close to the theoretical mass calculated from the balanced chemical equation. The percent error should be relatively small, indicating that the law of conservation of mass is followed and the stoichiometry of the reaction is confirmed.

Possible Sources of Error:

Several factors could contribute to errors in this experiment:

• Incomplete decomposition of KClO3: If the KClO3 is not heated sufficiently, it may not completely decompose, leading to a lower experimental mass of oxygen produced.
• Loss of KCl or MnO2: Some KCl or MnO2 may be lost during the heating process, leading to a lower mass after heating and an overestimation of the mass of oxygen produced.
• Inaccurate weighing: Errors in weighing the test tube, KClO3, or the contents after heating can lead to significant errors in the calculations.
• Moisture absorption: KClO3 and KCl are hygroscopic and can absorb moisture from the air, leading to inaccurate mass measurements.
• Side reactions: Although unlikely, side reactions could occur, leading to the formation of products other than KCl and O2, which would affect the mass balance.

Discussion Points:

• Discuss the importance of using a catalyst (MnO2) in this reaction. How does it affect the reaction rate?
• Explain how the law of conservation of mass is demonstrated in this experiment.
• Discuss the sources of error and how they could be minimized in future experiments.
• How would using a different catalyst affect the results?
• What are the environmental considerations for disposing of the chemicals used in this experiment?
• How can the results of this experiment be used in other areas of chemistry, such as determining the purity of a sample or calculating the yield of a reaction?

Safety Precautions

• Wear safety goggles at all times to protect your eyes from chemical splashes or flying debris.
• Handle potassium chlorate with care. It is a strong oxidizing agent and can react violently with combustible materials.
• Use a test tube clamp to hold the test tube while heating. Do not hold the test tube in your hand.
• Point the mouth of the test tube away from yourself and others while heating to avoid injury from any ejected material.
• Do not heat the test tube too rapidly, as this can cause the KClO3 to decompose too quickly and splatter.
• Allow the test tube to cool completely before weighing it to avoid burns.
• Dispose of the chemicals properly according to your instructor's instructions.
• Tie long hair back and secure loose clothing to prevent accidents with the Bunsen burner.
• Be aware of the location of the fire extinguisher and other safety equipment in the laboratory.
• Report any spills or accidents to your instructor immediately.

Conclusion

This experiment provides valuable insight into the stoichiometry of chemical reactions and the law of conservation of mass. By carefully measuring the mass of reactants and products, we can verify the quantitative relationships inherent in a balanced chemical equation. The experiment also highlights the importance of accurate measurements, careful technique, and awareness of potential sources of error in experimental work. The decomposition of potassium chlorate serves as a practical example of how chemical reactions can be used to produce specific products in predictable quantities. By understanding the principles underlying this reaction, students can gain a deeper appreciation for the quantitative nature of chemistry and its applications in various fields.

Frequently Asked Questions (FAQ)

• Why is manganese dioxide used in this experiment?

  Manganese dioxide (MnO2) is used as a catalyst. A catalyst speeds up the rate of a chemical reaction without being consumed in the reaction itself. In this case, MnO2 lowers the activation energy required for the decomposition of potassium chlorate (KClO3), allowing the reaction to occur at a lower temperature and at a faster rate.

• What happens if the potassium chlorate is not heated enough?

  If the potassium chlorate (KClO3) is not heated sufficiently, it may not completely decompose into potassium chloride (KCl) and oxygen gas (O2). This incomplete decomposition would result in a lower mass of oxygen produced, leading to a lower experimental value and a higher percent error. It's crucial to heat the KClO3 until no more oxygen gas is evolved, which can be tested using a glowing splint.

• How can the percent error be reduced in this experiment?

  To reduce the percent error, several precautions can be taken:

  • Ensure complete decomposition of KClO3 by heating it thoroughly until no more oxygen gas is produced.
  • Avoid any loss of material (e.g., KCl or MnO2) during the heating process.
  • Use an accurate balance for weighing the test tube and its contents.
  • Handle hygroscopic substances carefully to minimize moisture absorption.
  • Repeat the experiment multiple times and calculate the average mass of oxygen produced for more reliable results.

• Is potassium chlorate dangerous?

  Yes, potassium chlorate (KClO3) can be dangerous if not handled properly. It is a strong oxidizing agent and can react violently with combustible materials, potentially causing fires or explosions. It should be handled with care, kept away from flammable substances, and used in a well-ventilated area. Always wear safety goggles and follow the safety precautions outlined in the experimental procedure.

• What is the purpose of testing for oxygen gas with a glowing splint?

  The glowing splint test is a common method to confirm the presence of oxygen gas (O2). Oxygen supports combustion, so when a glowing splint is inserted into a test tube containing oxygen, the splint will re-ignite. This is a clear indication that oxygen gas is being produced in the reaction. If the splint does not re-ignite, it suggests that the reaction is either not producing oxygen or the concentration of oxygen is too low to support combustion.

• What is the role of the balanced chemical equation in this experiment?

  The balanced chemical equation (2 KClO3(s) → 2 KCl(s) + 3 O2(g)) is essential for this experiment because it provides the stoichiometric ratios between the reactants and products. These ratios are used to calculate the theoretical mass of oxygen that should be produced from a given mass of potassium chlorate. By comparing the experimental mass of oxygen produced with the theoretical mass, we can verify the stoichiometry of the reaction and assess the accuracy of the experimental results.

• How does this experiment demonstrate the law of conservation of mass?

  This experiment demonstrates the law of conservation of mass by showing that the total mass of the reactants (KClO3) is equal to the total mass of the products (KCl and O2). The potassium chlorate decomposes into potassium chloride and oxygen gas, and the mass of oxygen produced can be calculated by subtracting the mass of the remaining potassium chloride and manganese dioxide from the initial mass of potassium chlorate. Ideally, the experimental mass of oxygen produced should be close to the theoretical mass calculated from the balanced chemical equation, thus verifying that mass is neither created nor destroyed in the chemical reaction.

• Can other catalysts be used in place of manganese dioxide?

  Yes, other catalysts can be used in place of manganese dioxide (MnO2), but the effectiveness may vary. Some alternative catalysts include iron(III) oxide (Fe2O3) and copper(II) oxide (CuO). The choice of catalyst can affect the rate of the reaction and the temperature required for the decomposition of potassium chlorate. MnO2 is commonly used because it is readily available and effective at lowering the activation energy of the reaction.

• How would impurities in the potassium chlorate sample affect the results?

  Impurities in the potassium chlorate (KClO3) sample can significantly affect the results of the experiment. If the sample contains impurities, the measured mass of KClO3 will include the mass of the impurities, leading to an overestimation of the amount of KClO3 present. This, in turn, would affect the calculations for the theoretical mass of oxygen produced, resulting in inaccurate results and a higher percent error. It is important to use a pure sample of KClO3 to ensure accurate and reliable results.

• What are the environmental considerations for this experiment?

  Environmental considerations for this experiment include the proper disposal of the chemicals used. Potassium chlorate and potassium chloride should not be disposed of down the drain. Instead, they should be collected and disposed of according to your institution's guidelines for chemical waste disposal. Manganese dioxide is generally considered safe but should still be disposed of properly. It's important to minimize the amount of chemicals used and to follow all safety and environmental regulations to prevent pollution and protect the environment.

This detailed report provides a comprehensive understanding of Experiment 10, covering the essential aspects from introduction to conclusion, along with frequently asked questions to reinforce learning.