Report For Experiment 10 Composition Of Potassium Chlorate

Here's a sample report on the experiment focusing on the composition of potassium chlorate.

Experiment 10: Composition of Potassium Chlorate

Abstract

This experiment aims to determine the weight percentage of oxygen in potassium chlorate ($KClO_3$) through the thermal decomposition of a known mass of the compound. By carefully measuring the mass of $KClO_3$ before and after heating, the mass of oxygen released can be calculated. This allows us to experimentally determine the composition of potassium chlorate and compare it to the theoretical value. Precise measurement techniques and data analysis are crucial for accurate results and a comprehensive understanding of stoichiometry and chemical reactions.

Introduction

Potassium chlorate ($KClO_3$) is a strong oxidizing agent commonly used in various applications, including explosives, disinfectants, and oxygen production. When heated, $KClO_3$ undergoes thermal decomposition, breaking down into potassium chloride ($KCl$) and oxygen gas ($O_2$). This decomposition reaction is described by the following balanced chemical equation:

$2KClO_3(s) \rightarrow 2KCl(s) + 3O_2(g)$

Understanding the composition of chemical compounds is fundamental in chemistry. The law of definite proportions states that a chemical compound always contains the same elements in the same proportions by mass. This experiment provides a practical approach to verifying this law by quantitatively analyzing the decomposition of $KClO_3$.

By accurately measuring the mass of $KClO_3$ before and after decomposition, we can determine the mass of oxygen released during the reaction. This experimental data allows us to calculate the weight percentage of oxygen in the original $KClO_3$ sample. Comparing this experimental percentage with the theoretical percentage calculated from the chemical formula provides insights into the accuracy of our experimental technique and the validity of the law of definite proportions. This experiment also reinforces essential laboratory skills, including precise measurement, data recording, and error analysis.

Materials and Methods

To ensure accurate results, meticulous preparation and execution are essential. This section outlines the materials required and the step-by-step procedure followed.

Materials

• Potassium chlorate ($KClO_3$)
• Manganese dioxide ($MnO_2$) (catalyst)
• Test tube
• Test tube clamp
• Bunsen burner
• Electronic balance (accurate to 0.001 g)
• Crucible and lid
• Clay triangle
• Ring stand
• Spatula
• Glass stirring rod
• Safety goggles
• Lab coat

Procedure

1. Preparation of Apparatus:
   • Clean and thoroughly dry the test tube and crucible. Impurities or moisture can affect the accuracy of mass measurements.
   • Set up the ring stand with the clay triangle. Place the crucible on the clay triangle, ensuring it is stable.
2. Weighing the Reactants:

   • Accurately weigh the clean, dry test tube using the electronic balance and record the mass ($m_{tube}$).

   • Add approximately 2-3 grams of potassium chlorate ($KClO_3$) to the test tube.

   • Weigh the test tube containing the $KClO_3$ and record the mass ($m_{tube + KClO_3}$).

   • Calculate the mass of $KClO_3$ ($m_{KClO_3}$) by subtracting the mass of the empty test tube from the mass of the test tube with $KClO_3$:

     $m_{KClO_3} = m_{tube + KClO_3} - m_{tube}$

   • Add a small amount of manganese dioxide ($MnO_2$), which acts as a catalyst, to the $KClO_3$ in the test tube. Mix thoroughly with a clean glass stirring rod. The catalyst speeds up the reaction without being consumed.

3. Heating the Potassium Chlorate:
   • Secure the test tube with a test tube clamp and position it at an angle on the ring stand.
   • Begin heating the test tube gently with a Bunsen burner. Move the flame along the length of the test tube to ensure uniform heating.
   • As the $KClO_3$ decomposes, oxygen gas will be evolved. Continue heating until no more oxygen gas is visibly produced. This can be confirmed by observing that the bubbling or sparking has ceased.
   • Heat the test tube strongly for an additional 5 minutes to ensure complete decomposition of the $KClO_3$.
4. Cooling and Weighing the Residue:
   • Turn off the Bunsen burner and allow the test tube to cool to room temperature. Cooling should be done in a desiccator to prevent moisture absorption.
   • Once cooled, weigh the test tube containing the residue (potassium chloride and manganese dioxide) and record the mass ($m_{tube + residue}$).
5. Calculating the Mass of Oxygen Released:

   • Calculate the mass of the residue ($m_{residue}$) by subtracting the mass of the empty test tube from the mass of the test tube with the residue:

     $m_{residue} = m_{tube + residue} - m_{tube}$

   • Determine the mass of oxygen released ($m_{O_2}$) by subtracting the mass of the residue from the initial mass of the $KClO_3$:

     $m_{O_2} = m_{KClO_3} - m_{residue}$

6. Calculating the Weight Percentage of Oxygen:

   • Calculate the experimental weight percentage of oxygen in the potassium chlorate by dividing the mass of oxygen released by the initial mass of the potassium chlorate, then multiply by 100:

     $%O_2 = \frac{m_{O_2}}{m_{KClO_3}} \times 100$

7. Theoretical Calculation:

   • Calculate the theoretical weight percentage of oxygen in $KClO_3$ using the molar masses of potassium (K), chlorine (Cl), and oxygen (O). The molar masses are approximately:

     • K = 39.10 g/mol
     • Cl = 35.45 g/mol
     • O = 16.00 g/mol

   • The molar mass of $KClO_3$ is:

     $M_{KClO_3} = 39.10 + 35.45 + (3 \times 16.00) = 122.55 , g/mol$

   • The mass of oxygen in one mole of $KClO_3$ is:

     $3 \times 16.00 = 48.00 , g/mol$

   • The theoretical weight percentage of oxygen in $KClO_3$ is:

     $%O_2 , (theoretical) = \frac{48.00}{122.55} \times 100$

8. Error Analysis:

   • Calculate the percent error by comparing the experimental weight percentage to the theoretical weight percentage:

     $% , error = \frac{|%O_2 , (experimental) - %O_2 , (theoretical)|}{%O_2 , (theoretical)} \times 100$

Safety Precautions

• Always wear safety goggles to protect your eyes from chemical splashes and fumes.
• Handle potassium chlorate with care, as it is a strong oxidizing agent and can react violently with combustible materials.
• Perform the experiment in a well-ventilated area to avoid inhaling harmful fumes.
• Use a test tube clamp to hold the test tube while heating to avoid burns.
• Allow the test tube to cool completely before weighing to prevent inaccurate measurements.
• Dispose of chemical waste properly according to laboratory guidelines.

Results

This section presents the data collected during the experiment and the subsequent calculations.

Data Table

Calculations

1. Experimental Weight Percentage of Oxygen:

   $%O_2 , (experimental) = \frac{0.788}{2.515} \times 100 = 31.33%$

2. Theoretical Weight Percentage of Oxygen:

   $%O_2 , (theoretical) = \frac{48.00}{122.55} \times 100 = 39.17%$

3. Percent Error:

   $% , error = \frac{|31.33 - 39.17|}{39.17} \times 100 = 19.99%$

Discussion

The experimental weight percentage of oxygen in potassium chlorate was found to be 31.33%, while the theoretical value is 39.17%. This resulted in a percent error of 19.99%. Several factors could have contributed to this discrepancy.

Possible Sources of Error

• Incomplete Decomposition: If the potassium chlorate was not completely decomposed during heating, some unreacted $KClO_3$ would remain in the test tube, leading to an overestimation of the mass of the residue and an underestimation of the mass of oxygen released. This is the most likely source of error.
• Loss of Reactant: During heating, some $KClO_3$ might have been lost due to sputtering or sublimation, even though this is less probable. This would also lead to an underestimation of the mass of oxygen released.
• Impure Reactants: The presence of impurities in the potassium chlorate sample could affect the accuracy of the results. Impurities could either react during heating, adding to the mass of the residue, or they might not decompose, leading to an overestimation of the residue mass.
• Measurement Errors: Inaccurate measurements of the masses of the test tube, $KClO_3$, and residue could also contribute to the error. Parallax errors when reading the balance, or fluctuations in the balance reading, could lead to inaccuracies.
• Moisture Absorption: If the test tube and residue were not completely dry before weighing, or if they absorbed moisture from the air during cooling, this would lead to an overestimation of the mass of the residue.
• Catalyst Effects: The catalyst, manganese dioxide ($MnO_2$), may not have been uniformly mixed with the $KClO_3$, affecting the rate and completeness of the decomposition.

Error Mitigation Strategies

• Prolonged Heating: To ensure complete decomposition of the potassium chlorate, the sample should be heated for an extended period, and the absence of further oxygen evolution should be confirmed.
• Accurate Weighing: Use a calibrated electronic balance and ensure accurate weighing techniques to minimize measurement errors.
• Drying Procedures: Ensure that all glassware is thoroughly dry before use, and cool the test tube and residue in a desiccator to prevent moisture absorption.
• Pure Reactants: Use high-purity potassium chlorate to minimize the effects of impurities on the results.
• Uniform Mixing: Ensure that the catalyst is uniformly mixed with the $KClO_3$ to promote consistent decomposition.
• Controlled Heating: Maintain a consistent and controlled heating rate to prevent sputtering or sublimation of the sample.

Conclusion

The experiment aimed to determine the weight percentage of oxygen in potassium chlorate through thermal decomposition. While the experimental result of 31.33% deviated from the theoretical value of 39.17%, the experiment provided valuable insights into stoichiometry, chemical reactions, and error analysis. The significant percent error of 19.99% indicates that there were likely experimental errors, such as incomplete decomposition, measurement inaccuracies, or the presence of impurities.

To improve the accuracy of future experiments, it is recommended to implement the error mitigation strategies discussed, including prolonged heating, accurate weighing techniques, drying procedures, and the use of pure reactants. By addressing these potential sources of error, the experimental results can be brought closer to the theoretical values, providing a more accurate determination of the composition of potassium chlorate. This experiment reinforces the importance of careful experimental design, precise measurement, and thorough data analysis in quantitative chemistry. Furthermore, understanding the composition of compounds such as potassium chlorate is crucial in various fields, including chemical synthesis, industrial processes, and environmental monitoring.

Frequently Asked Questions (FAQ)

• What is the purpose of using manganese dioxide ($MnO_2$) in this experiment?

  Manganese dioxide acts as a catalyst in the decomposition of potassium chlorate. A catalyst speeds up the reaction without being consumed itself. In this case, $MnO_2$ lowers the activation energy required for the decomposition of $KClO_3$, allowing the reaction to proceed at a lower temperature and at a faster rate.

• Why is it important to heat the potassium chlorate slowly and gradually?

  Heating the potassium chlorate slowly and gradually is important to prevent the sample from sputtering or sublimating out of the test tube. Rapid heating can cause the $KClO_3$ to decompose too quickly, leading to a loss of material and inaccurate results. Gradual heating ensures a controlled decomposition process.

• How do you know when the potassium chlorate has completely decomposed?

  The potassium chlorate has completely decomposed when no more oxygen gas is visibly evolved from the test tube. This can be observed by the cessation of bubbling or sparking. To ensure complete decomposition, it is recommended to continue heating the sample strongly for an additional 5 minutes after the visible signs of reaction have stopped.

• What are the safety precautions to consider when handling potassium chlorate?

  Potassium chlorate is a strong oxidizing agent and should be handled with care. Always wear safety goggles to protect your eyes from chemical splashes and fumes. Perform the experiment in a well-ventilated area to avoid inhaling harmful fumes. Use a test tube clamp to hold the test tube while heating to avoid burns. Dispose of chemical waste properly according to laboratory guidelines. Avoid contact with combustible materials, as $KClO_3$ can react violently with them.

• What is the significance of calculating the percent error in this experiment?

  Calculating the percent error is important for evaluating the accuracy and reliability of the experimental results. The percent error provides a quantitative measure of the difference between the experimental value and the theoretical value. A high percent error indicates that there were significant experimental errors, while a low percent error suggests that the experimental technique was accurate and reliable. Analyzing the percent error helps identify potential sources of error and improve the experimental procedure.

• How does this experiment relate to the Law of Definite Proportions?

  This experiment directly relates to the Law of Definite Proportions, which states that a chemical compound always contains the same elements in the same proportions by mass. By experimentally determining the mass of oxygen in a known mass of potassium chlorate, we can verify whether the ratio of oxygen to potassium and chlorine is consistent with the chemical formula $KClO_3$. A significant deviation from the theoretical composition would suggest that the sample is impure or that there were significant experimental errors.

This comprehensive report provides a detailed account of the experiment on the composition of potassium chlorate. By following the procedures outlined and considering the potential sources of error, students can gain a deeper understanding of stoichiometry, chemical reactions, and quantitative analysis.