Table of Contents

Title page. 1

Table of tables. 2

Introduction. 3

Background. 3

Purpose of the Laboratory Experiment. 4

The procedure of Experiment 4

Results. 5

Data Tables. 5

Observation. 6

Data Analysis. 7

Calculations. 7

Discussion. 9

References. 11

 

Table of tables

Table 1: Measurements for heating KClO₃. 5

Table 2: Measurements for heating unknown substance. 6

 

 

 

 

 

 

 

 

 

 

 

 

Introduction

Background

Determining the amount of components of organometallic complexes in a chemical reaction involves a step-by-step procedural calculation of numerical relationship for the values of for each reactant. This calculation involves the use of formulas and ratios for finding chemical amounts for different solutions for unknown values of products using known values of rea or reactants or products. Also, such calculations are only achieved by carefully determining a balanced chemical equation for the reaction involved in the process. In chemistry, such calculations in a laboratory experiment for determining unknown values of chemical amounts of either products or reactants involves use of stoichiometry. Stoichiometry is based on various common classifications of chemical reactions including precipitation, acid-base and oxidation-reduction reactions. Basically, stoichiometry can be described as a quantitative assessment of relationships between the chemical amounts of reactants used and the products formed in a chemical reaction based on chemical formulas and molecular coefficients (Vogt, 2017). On the other hand, catalysis involves the use of a chemical substance or a condition to increase the rate of a reaction in a chemical reaction. However, such substance does not appear in the net chemical equation nor get consumed during the reaction.

The laboratory experiment carried out involved thermolysis or thermal decomposition process for chemical compounds. Thermolysis is a process in which a compound is decomposed into its component elements by use of heat. The amount of the element decomposed from the process can be therefore determined by carrying out stoichiometry based on the balanced chemical equations, molecular mass, and percentage coefficients. During thermolysis, catalysts play an important role in increasing the rate of decomposition to reduce the time required for decomposition.

Purpose of the Laboratory Experiment

The experiment involves the utilization of thermal decomposition, catalysis, and stoichiometry to determine the amount of oxygen that can be removed from the heating potassium chlorate compound. During the experiment, potassium chlorate (KClO₃) is heated to drive off oxygen leaving behind potassium chloride (KCl). The molecular mass of the compounds before and after thermal decomposition is then used in stoichiometry to determine the molecular mass of oxygen removed during the process.

The procedure of the Experiment

The experiment was performed by paying attention to the instructions provided and the safety precautions in every stage of the experiment. The two Pyrex test-tubes required for the experiment were obtained and thoroughly cleaned and labeled with the reactants. One of the test-tube was labeled (KClO₃) while the other test-tube labeled “UNKNOWN”. For 1-2minutes, each test-tube was heated over a Bunsen burner to remove moisture. Then, Manganese (IV) oxide (MnO₂) is used as a catalyst by adding small amounts to each labeled test-tube. The test-tubes were positioned using ring stand and a clamp slanting 45 degrees away from people when heating. After each test-tube was heated, the tubes were removed and allowed to cool for about five minutes on a wire gauze. To obtain the initial mass of the test-tube and the catalyst, each labeled test-tube was weighed and the initial mass recorded.

Thereafter, about 1 gram of potassium chlorate was placed in a KClO₃ labeled test-tube and the mass of the test-tube and its content measured. To ensure that KClO₃ and Mn0₂ were thoroughly mixed, the test-tube was swirled. The test-tube was then clamped to a ring stand slant at 45 degrees away from people and heated for about 8 minutes until the components of the test-tube turned dark-grey solid. Then the test-tube was detached and allowed to cool on a wire gauze.

Separately, about one gram of an unknown substance was placed in the test-tube labeled unknown and its mass weighed and recorded. Then the unknown substance was mixed with the catalyst by swirling the test-tube. Using a clamp, the test-tube was attached to the ring stand slanting 45 degrees away from people. Then the test-tube was heated using a Bunsen burner for about 8 minutes until the substance solidifies and a noticeable dark grey color observed. Then the test-tube was removed and allowed to cool on wire gauze for about 5 minutes.

The cooled test-tubes were then reweighed and their masses recorded. To obtain accuracy on the final mass of the test-tube and their components, both test-tubes were repeatedly set up and reheated for about 4 times and reweighed again. The data obtained from the weights of the test-tubes before and after the three heating experiments were recorded in Table 1 for the KClO₃ and Table 2 for the unknown substance.

Results

Data Tables

Table 1: Measurements for heating KClO₃

	Mass (g)	Difference(g)
Weight of test tube + MnO2	45.069
Weight of test tube + MnO2+ KClO3	46.561
Weight after 1st heating	46.435
Weight after 2nd heating	46.358	0.079
Weight after 3rd heating	46.341	0.015
Constant Weight	46.378

 

 

Table 2: Measurements for a heating unknown substance

	Mass (g)	Difference(g)
Weight of test tube + MnO2	45.059
Weight of test tube + MnO2+ Unknown	46.310
Weight after 1st heating	46.111
Weight after 2nd heating	46.092	0.019
Weight after 3rd heating	46.076	0..016
Constant Weight	46.093

 

Observation

During the heating process, the potassium chlorate in test-tube labeled KClO₃ solidified and turned dark grey. The unknown substance in the test-tube labeled “UNKNOWN” also solidified and turned dark grey after heating.

Data Analysis

Calculations

1. Determine the weight of KClO₃

From the test-tube labeled KClO₃;

Weight of KClO₃ = (weight of test tube + MnO₂ + KClO₃) – (weight of test-tube +MnO₂)

= 46.561 g – 45.069 g

= 1.492 g

2. Determine the weight of the oxygen gas lost

Weight of the oxygen gas removed = (Weight of test tube + MnO₂ + KClO₃) – (constant weight)

= 46.561 g – 46.378 g

= 0.183 g

3. Based on the values obtained above determine the experimental percent of oxygen in KClO₃

= 12.26% O₂

4. Determine the theoretical percentage of oxygen present in KClO₃

Molecular mass of KClO₃ =122.5495 g/mol

Molecular mass of O₃ = 47.9982 g/mol

The theoretical percentage of oxygen =

= 39.12%

5. Determine the percentage error for obtaining the percentage of oxygen in KClO₃

Percentage error =

=  = 31.34%

From Data Table 2

1. Determine the weight of the unknown substance

Weight of KClO₃ = (weight of test tube + MnO₂ + KClO₃) – (weight of test-tube +MnO₂)

= 46.310 g – 45.059 g

= 1.251 g

2. Determine the weight of the oxygen gas lost sing the constant weight

Weight of the oxygen gas removed = (Weight of test tube + MnO₂ + unknown substance) – (constant weight)

= 46.310 g – 46.093 g

= 0.217 g

3. Determine the number of moles of oxygen gas lost

Molecular mass of oxygen gas = 32.0 g/mol

Moles of oxygen gas lost =  =  = 0.006781 moles

4. Using stoichiometry, determine the number of moles of KClO₃ decomposed

The chemical equation for the reaction is;

2KClO₃→ 2 KCl + 6 O₂

Therefore the moles of KClO₃ =

× 2 = 0.00226 moles of KClO₃

5. Determine the number of grams of KClO₃ decomposed given that the molecular weight of KClO₃ is 122.5 g/mol

Weight of KClO₃ = moles of KClO₃ × Molecular weight of KClO₃

= 0.00226 moles × 122.5g/mol

= 0.2769 g

6. Determine the percentage of KClO₃ present in the unknown substance

Total weight of unknown substance = 1.251g

Percentage of KClO₃ =

=

= 22.13%

Discussion

The objectives of this laboratory experiment were to determine the percentage of molecules in a compound using a series of steps and stoichiometry. The experiment was aimed at determining the chemical amounts of known substance involved in a chemical reaction. The experiment was carried out successfully and the data obtained and recorded were effective in achieving the objectives of the experiment. Nonetheless, there were challenges and shortcomings on the observations and the determined values obtained through stoichiometry. Although attention was paid to all procedures and instruction given, other conditions such as temperatures led to inconsistency of the obtained results with the theoretical values.

The obtained results showed that 12.26% of oxygen was present in the potassium chlorate compound and 22.13% of potassium chlorate was present in the unknown substance heated. The analysis of the results obtained also shows that the percentage error in the calculation of the removed oxygen can be attributed to challenges encountered in heating the compound and accuracy of measurements taken. The source of errors witnessed in analysis and interpretation of results include incomplete heating of the samples, poor accuracy of balances used to measure the weight of the samples and human error in recording and calculations of obtained value

 

 

 

 

 

 

 

 

 

 

 

 

References

Lab, B. (2019). Stoichiometry and Catalysis: Validation Experiment. DeltaScope datasets. doi:10.35482/bld.002.2019

Morales, Z.C., Moore, Howard; Xie-Wang, Hong. 1997. Percentage of Oxygen in a Compound: Stoichiometry and Catalysis. In Laboratory Manual General Chemistry 1. Florida International University, pg 73-76

Vogt, J. (2017). Stoichiometry and Chemical Reactions. Exam Survival Guide: Physical Chemistry, 9-16. doi:10.1007/978-3-319-49810-2_2

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