Quantitative Analysis of an Aluminum-Zinc Alloy: Evaluating Composition through Hydrogen Evolution

Categories: Chemistry

Analysis, Pages 4 (774 words)

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Introduction

Chemical stoichiometry lies at the heart of analytical chemistry, providing insights into the quantitative relationships between reactants and products in chemical reactions. This foundational principle is crucial when analyzing alloys—a mixture of metals that exhibit properties distinct from their constituent elements. The experiment conducted by Tamari Pirtskhalava and Lado Shapakidze on October 4, 2019, in the CHEM 200, Group 3 laboratory, delves into the analytical techniques used to determine the composition of an aluminum-zinc alloy. This detailed investigation aimed to quantify the hydrogen gas evolved from the interaction of the alloy with a strong acid and subsequently calculate the percent composition of aluminum and zinc within the alloy.

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Purpose of the Experiment

The experiment was designed to dissect the stoichiometric relationships governing the reactions between aluminum, zinc, and a strong acid to produce hydrogen gas. The overarching goal was to apply these stoichiometric principles to deduce the precise composition of an aluminum-zinc alloy, providing a clear understanding of the alloy's chemical makeup. Such analysis is pivotal in materials science, where the properties of alloys depend significantly on their constituent proportions.

Methodology

Experimental Procedure

The experiment was segmented into three distinct parts:

Part A: Focused on the reaction of aluminum with the acid to measure the volume of hydrogen gas evolved.
Part B: Similar to Part A but centered on the reaction of zinc with the acid.
Part C: Aimed at analyzing a specific aluminum-zinc alloy to determine its precise composition by measuring the evolved hydrogen gas.

Part A

Mass of aluminum (g)	0.026
Initial volume (mL)	1.70
Final volume (mL)	41.70
Difference (mL)	40.0
Height of water in the column (cm)	34.8
Room temperature (Celsius)	27.0
(atm)	0.0352
(atm)	0.952

Part B

Mass of zinc (g)	0.112
Initial volume (mL)	8.90
Final volume (mL)	54.40
Difference (mL)	45.5
Height of the water in the column (cm)	29.10
Room temperature (Celsius)	27.0
(atm)	0.0352
(atm)	0.952

Part C

Mass of aluminum-zinc alloy #C (g)	0.119
Initial volume (mL)	1.80
Final volume (mL)	82.60
Difference (mL)	80.8
Height of water in the column (cm)	13.70
Room temperature (Celsius)	24.2
(atm)	0.0294
(atm)	0.952

Each part involved measuring the mass of the metal (or alloy), the initial and final volumes of gas collected, and additional parameters such as room temperature and atmospheric pressure, which are critical for accurate gas volume measurements.

Data Collection

The experiment yielded quantitative data on the mass of the metals and the alloy, the change in gas volume during the reactions, and the ambient conditions under which the experiments were conducted. This data served as the foundation for subsequent calculations.

Calculated Results and Analysis

Stoichiometric Calculations

The experiment's crux involved converting the measured gas volumes to moles of hydrogen gas using the ideal gas law, which then allowed for the calculation of the metals' percent composition in the alloy. This process required careful temperature adjustments to Kelvin and the application of atmospheric pressure corrections to ensure accuracy.

For Aluminum and Zinc: The actual and theoretical yields of hydrogen gas were calculated, providing a basis for determining the percent yield of the reactions.
For the Aluminum-Zinc Alloy: The experiment calculated the mass and percent composition of aluminum and zinc in the alloy, utilizing the total mass of the alloy and the mass of hydrogen gas evolved as a proxy for the reaction's completeness.

Discussion on Accuracy and Precision

The experiment's accuracy was gauged by comparing the actual yield of hydrogen gas to its theoretical yield, with percent yields for aluminum and zinc reactions indicating a high level of accuracy. However, the absence of multiple trials for each part of the experiment means that precision, defined as the consistency of measurement results, could not be reliably assessed.

Systematic errors, such as inaccurate atmospheric pressure or temperature measurements, could skew results, while random errors—like misreading measurements—present additional uncertainties. The alloy's assumed purity was critical; any contaminants would have introduced significant errors in the final composition analysis.

Conclusion

The analytical investigation into the aluminum-zinc alloy's composition underscored the importance of stoichiometry in understanding chemical reactions and materials' properties. Despite potential sources of error, the experiment achieved a high degree of accuracy in determining the alloy's composition. This success illustrates the power of chemical stoichiometry in practical applications, from materials science to industrial manufacturing, where understanding an alloy's makeup is crucial for its application. Future experiments could enhance precision by incorporating multiple trials and employing more sophisticated measurement techniques to mitigate systematic and random errors.

In summary, the experiment not only achieved its primary objective of analyzing the aluminum-zinc alloy's composition but also highlighted the integral role of stoichiometry in chemical analysis. Through careful experimental design, rigorous data collection, and detailed analysis, the study provided valuable insights into the quantitative aspects of chemical reactions, contributing to the broader field of analytical chemistry.