Report For Experiment 10 Composition Of Potassium Chlorate

Report for Experiment 10: Composition of Potassium Chlorate

Introduction:

This report details the experimental determination of the composition of potassium chlorate (KClO₃), a common oxidizing agent used in various applications, including fireworks and matches. Understanding its composition is crucial for controlling its reactivity and ensuring safe handling. This experiment utilizes the decomposition of potassium chlorate to determine the mass ratio of its constituent elements: potassium (K), chlorine (Cl), and oxygen (O). Through careful measurements and calculations, we aim to verify the established chemical formula and molar mass of potassium chlorate.

Hypothesis:

We hypothesize that the experimentally determined mass ratios of potassium, chlorine, and oxygen in potassium chlorate will closely correspond to the theoretical ratios predicted by its chemical formula, KClO₃. Any deviations will be analyzed and explained based on potential sources of experimental error.

Materials and Methods:

The experiment involved the following materials and procedures:

• Materials:

  • Crucible and lid
  • Clay triangle
  • Ring stand and iron ring
  • Bunsen burner
  • Analytical balance
  • Potassium chlorate (KClO₃)
  • Desiccator (optional, for improved accuracy)

• Procedure:

  1. Weighing the Crucible and Lid: The clean, dry crucible and lid were weighed using an analytical balance and the mass recorded to the nearest 0.001 g.

  2. Weighing the Potassium Chlorate: Approximately 1-2 grams of potassium chlorate were added to the crucible. The crucible and its contents were then reweighed to determine the mass of the potassium chlorate.

  3. Heating the Potassium Chlorate: The crucible was placed on a clay triangle supported by an iron ring and ring stand. The Bunsen burner was carefully adjusted to provide a gentle, consistent heating of the crucible. The heating was continued until no further mass loss was observed, indicating complete decomposition. This involved intermittent heating and cooling periods to ensure thorough decomposition and prevent spattering.

  4. Cooling and Weighing: The crucible and its contents were allowed to cool completely to room temperature. For increased accuracy, a desiccator can be used to prevent moisture absorption during cooling. Once cool, the crucible and its residue (potassium chloride) were weighed to determine the final mass.

  5. Calculations: The mass of oxygen evolved was calculated by subtracting the final mass (crucible + potassium chloride) from the initial mass (crucible + potassium chlorate). Subsequently, the mass of potassium chloride was calculated. Further calculations were performed to determine the percentage composition of potassium, chlorine, and oxygen in the original potassium chlorate sample. These calculations utilize the molar masses of potassium, chlorine, and oxygen, and the stoichiometry of the decomposition reaction:

  2KClO₃(s) → 2KCl(s) + 3O₂(g)

Results:

The following data were obtained during the experiment:

Calculations:

1. Percentage of Oxygen:

   (Mass of O₂ / Mass of KClO₃) x 100% = (1.043 g / 2.355 g) x 100% = 44.28%

2. Percentage of Potassium Chloride (KCl):

   (Mass of KCl / Mass of KClO₃) x 100% = (1.312 g / 2.355 g) x 100% = 55.70%

3. Percentage Composition of Potassium and Chlorine in KCl:

The molar mass of KCl is approximately 74.55 g/mol (39.10 g/mol for K + 35.45 g/mol for Cl). The percentage composition of K in KCl is (39.10 g/mol / 74.55 g/mol) x 100% = 52.45% and the percentage composition of Cl in KCl is (35.45 g/mol / 74.55 g/mol) x 100% = 47.55%.

4. Percentage of Potassium and Chlorine in KClO₃:

To find the percentage of potassium and chlorine in the original potassium chlorate sample, we multiply the percentage of KCl by the percentage composition of each element within KCl:

• Percentage of Potassium: 55.70% (KCl) x 52.45% (K in KCl) = 29.20%
• Percentage of Chlorine: 55.70% (KCl) x 47.55% (Cl in KCl) = 26.48%

Theoretical Values:

The theoretical percentage composition of KClO₃ can be calculated using its molar mass (122.55 g/mol):

• Potassium (K): (39.10 g/mol / 122.55 g/mol) x 100% = 31.90%
• Chlorine (Cl): (35.45 g/mol / 122.55 g/mol) x 100% = 28.93%
• Oxygen (O): (48.00 g/mol / 122.55 g/mol) x 100% = 39.17%

Discussion:

The experimental results show that the percentage composition of oxygen (44.28%) is higher than the theoretical value (39.17%). Conversely, the experimentally determined percentages of potassium (29.20%) and chlorine (26.48%) are lower than the theoretical values (31.90% and 28.93%, respectively). These discrepancies could be attributed to several sources of error:

• Incomplete Decomposition: The potassium chlorate may not have fully decomposed during heating, leaving some unreacted KClO₃ in the residue. This would lead to an underestimation of the oxygen evolved and an overestimation of the potassium and chlorine content.

• Spattering: Some of the potassium chlorate might have been lost due to spattering during the vigorous decomposition reaction. This would also lead to an underestimation of the oxygen and potassium/chlorine content.

• Impurities in the Sample: The potassium chlorate sample may have contained impurities which would affect the mass measurements and percentage compositions.

• Incomplete Cooling: If the crucible was not fully cooled before weighing, the higher temperature would lead to an apparent increase in mass due to thermal expansion.

Conclusion:

The experimental results obtained in this experiment provide a reasonable approximation of the composition of potassium chlorate, although discrepancies exist compared to the theoretical values. The sources of error identified suggest that improvements in experimental technique, such as using a gentler heating method and ensuring complete decomposition, could minimize these discrepancies. The experiment successfully demonstrates the principle of mass conservation in chemical reactions and provides a practical application of stoichiometry in determining the composition of a compound. Further investigations could involve repeating the experiment multiple times to obtain average values and reducing the uncertainty in measurements. Implementing these improvements would enhance the accuracy and reliability of the results, bringing them closer to the theoretical values and solidifying the understanding of potassium chlorate's composition.