Report For Experiment 10 Composition Of Potassium Chlorate

Experiment 10: Composition of Potassium Chlorate – A Comprehensive Report

This report details the experimental procedures, data analysis, and conclusions drawn from Experiment 10, focused on determining the composition of potassium chlorate (KClO₃). Understanding the precise composition of chemical compounds is fundamental in chemistry, impacting various fields from industrial production to environmental monitoring. This experiment utilizes a classic decomposition reaction to quantitatively analyze the components of potassium chlorate.

Introduction

Potassium chlorate (KClO₃) is a powerful oxidizing agent commonly used in fireworks, matches, and as a weed killer. Its chemical structure consists of one potassium (K⁺) cation and one chlorate (ClO₃⁻) anion. This experiment aims to determine the percentage by mass of potassium chloride (KCl) and oxygen (O₂) in potassium chlorate through thermal decomposition. By carefully measuring the mass before and after heating, we can calculate the mass of oxygen released and subsequently deduce the percentage composition. This process relies on the principle of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.

Objectives

The primary objectives of this experiment are:

• To experimentally determine the mass percentage of potassium chloride (KCl) in potassium chlorate (KClO₃).
• To experimentally determine the mass percentage of oxygen (O₂) in potassium chlorate (KClO₃).
• To compare the experimental results with the theoretical values calculated from the known molar masses of potassium, chlorine, and oxygen.
• To understand the principles of stoichiometry and the law of conservation of mass.
• To develop proficiency in laboratory techniques, including accurate mass measurement and careful heating.

Materials and Methods

Materials

• Potassium chlorate (KClO₃) – Ensure purity and handle with care.
• Crucible and lid – A high-temperature resistant crucible is essential.
• Clay triangle – To support the crucible during heating.
• Ring stand and iron ring – For stable support of the clay triangle.
• Bunsen burner – A reliable heat source for controlled heating.
• Analytical balance – Crucial for precise mass measurements.
• Spatula – For transferring the potassium chlorate.
• Desiccator (optional) – To prevent moisture absorption after heating.
• Goggles and lab coat – For safety.

Procedure

1. Weighing the Crucible and Lid: The crucible and lid were carefully cleaned and dried. Their combined mass was recorded using the analytical balance to the nearest 0.001g. This initial mass is crucial for subsequent calculations. Repeat this step at least three times for improved accuracy and to identify potential outliers.

2. Weighing the Potassium Chlorate: Approximately 1-2 grams of potassium chlorate was added to the pre-weighed crucible. The exact mass of potassium chlorate plus the crucible and lid was precisely recorded. Again, multiple measurements are recommended.

3. Heating the Crucible: The crucible, containing the potassium chlorate, was placed on the clay triangle supported by the ring stand. The Bunsen burner was lit, and the crucible was heated gently at first to avoid splattering. The temperature was gradually increased until the potassium chlorate completely decomposed, indicated by the cessation of gas evolution (oxygen). This process requires patience and careful observation. Sustained heating is needed to ensure complete decomposition.

4. Cooling and Weighing: After ensuring complete decomposition, the Bunsen burner was turned off, and the crucible was allowed to cool to room temperature. This step is critical to prevent errors caused by thermal expansion. A desiccator can be used to speed up cooling and prevent moisture absorption. Once cooled, the mass of the crucible, lid, and remaining potassium chloride was precisely measured.

5. Repeat and Replication: The entire process (steps 1-4) was repeated at least three times to ensure reproducibility and accuracy. Replication is fundamental in experimental science to minimize random errors and assess the reliability of results.

6. Data Recording: All mass measurements were meticulously recorded in a data table. This table should include the mass of the empty crucible and lid, the mass of the crucible, lid, and potassium chlorate before heating, and the mass of the crucible, lid, and potassium chloride after heating for each trial.

Results and Calculations

The following table represents a sample dataset from the experiment. Your results may vary depending on the amount of potassium chlorate used and the precision of your measurements.

Calculations:

For each trial:

1. Mass of KClO₃: Subtract the mass of the crucible and lid from the mass of the crucible, lid, and KClO₃.

2. Mass of Oxygen (O₂): Subtract the mass of the crucible, lid, and KCl from the mass of the crucible, lid, and KClO₃.

3. Percentage of KCl: (Mass of KCl / Mass of KClO₃) x 100%

4. Percentage of O₂: (Mass of O₂ / Mass of KClO₃) x 100%

Example Calculation (Trial 1):

• Mass of KClO₃ = 27.550 g - 25.500 g = 2.050 g
• Mass of O₂ = 27.550 g - 26.800 g = 0.750 g
• Percentage of KCl = (2.050 g - 0.750 g) / 2.050 g x 100% = 63.4%
• Percentage of O₂ = 0.750 g / 2.050 g x 100% = 36.6%

Discussion

The experimental results should be compared with the theoretical values. The theoretical percentage composition can be calculated using the molar masses of potassium (39.10 g/mol), chlorine (35.45 g/mol), and oxygen (16.00 g/mol). The molar mass of KClO₃ is 122.55 g/mol.

• Theoretical Percentage of KCl: (74.55 g/mol / 122.55 g/mol) x 100% ≈ 60.7%
• Theoretical Percentage of O₂: (48.00 g/mol / 122.55 g/mol) x 100% ≈ 39.2%

Error Analysis:

Discrepancies between experimental and theoretical values can be attributed to several factors:

• Incomplete Decomposition: If the heating was insufficient, some KClO₃ may remain undecomposed, leading to an underestimation of the oxygen percentage and an overestimation of the KCl percentage.

• Impurities in KClO₃: The presence of impurities in the initial potassium chlorate sample will affect the results.

• Measurement Errors: Errors in weighing can significantly affect the final calculations. Using an accurate analytical balance and employing proper weighing techniques is crucial to minimize this source of error.

• Loss of Sample: Some sample might be lost during heating due to splattering or sublimation. This would also affect the accuracy of the experiment.

• Moisture Absorption: If the cooled crucible was exposed to atmospheric moisture before weighing, the mass of the residue will be higher than expected, leading to errors in calculations.

Conclusion

This experiment successfully demonstrated the decomposition of potassium chlorate into potassium chloride and oxygen. The experimental results provided a quantitative measure of the composition of potassium chlorate, offering insights into the stoichiometry of the reaction. Although discrepancies exist between the experimental and theoretical values, these are explainable by the sources of error discussed above. Improved experimental techniques, such as using a more accurate balance and ensuring complete decomposition, can minimize these errors and improve the accuracy of the results. This experiment highlights the importance of careful experimental technique, accurate data recording, and a thorough understanding of error analysis in quantitative chemical analysis. Further experimentation with multiple trials and varying conditions could lead to a more precise and reliable determination of potassium chlorate's composition. The experiment successfully achieved its objectives, strengthening understanding of stoichiometry, mass conservation, and practical laboratory skills.