Lab: Synthesis and Analysis of Alum

Categories: Chemistry

Alum, a double sulfate salt with the formula KAl(SO4)2·12H2O, has various applications, including as a mordant in dyeing, in water purification, and as an ingredient in baking powder. This lab focuses on the synthesis of alum through a chemical reaction and subsequent analysis to determine its purity.

Procedure:

1. Synthesis of Alum:
• Mix 10 grams of aluminum foil with 50 mL of 1.4 M KOH solution in a flask.
• Add 150 mL of distilled water and heat the mixture until the aluminum dissolves.
• Slowly add 50 mL of 6 M H2SO4 while stirring to precipitate alum.
• Filter the mixture to separate the solid alum.
• Allow the filtrate to cool, then collect the alum crystals.
2. Analysis of Alum:
• Weigh the obtained alum crystals and record the mass.
• Perform a flame test to confirm the presence of potassium ions.
• Calculate the percent yield of alum using the formula: Percent Yield=(Actual YieldTheoretical Yield)×100Percent Yield=(Theoretical YieldActual Yield​)×100
• Perform a qualitative analysis to confirm the presence of sulfate ions using BaCl2 solution.

Calculations and Formulas:

1. Molar Mass of Alum: The molar mass of alum (KAl(SO4)2​⋅12H2O) can be calculated by summing the atomic masses of its constituent elements: Molar Mass=(2×Atomic Mass of K)+Atomic Mass of Al+(2×Atomic Mass of S)+(8×Atomic Mass of O)+(24×Atomic Mass of H)Molar Mass=(2×Atomic Mass of K)+Atomic Mass of Al+(2×Atomic Mass of S)+(8×Atomic Mass of O)+(24×Atomic Mass of H)
2. Theoretical Yield of Alum: The theoretical yield is the amount of alum that would be obtained if the reaction proceeded to completion.

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It can be calculated using stoichiometry.

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Theoretical Yield=Moles of Aluminum×Moles of AlumMoles of Aluminum×Molar Mass of AlumTheoretical Yield=Moles of Aluminum×Moles of AluminumMoles of Alum​×Molar Mass of Alum

3. Percent Yield: The percent yield indicates the efficiency of the reaction and is calculated using the formula mentioned earlier.

Results and Analysis:

Flame Test: The flame test is a qualitative analysis method to confirm the presence of potassium ions. A lilac flame color indicates the presence of potassium.

• Percent Yield: Utilizing the actual yield obtained from weighing the alum crystals and the theoretical yield calculated, the percent yield can be determined.
• Qualitative Analysis with BaCl2: The addition of BaCl2 solution to a solution of alum can confirm the presence of sulfate ions through the formation of a white precipitate (BaSO4).

Discussion:

1. Synthesis Process: Discuss the chemical reactions involved in each step of the alum synthesis. Explain why each reactant is used and the purpose it serves in the synthesis.
2. Calculations and Results: Present the calculated molar mass of alum, theoretical yield, and percent yield. Discuss any potential sources of error and their impact on the results.
3. Flame Test Results: Confirm the presence of potassium ions in the alum crystals using the flame test. Discuss the reliability of the flame test in qualitative analysis.
4. Qualitative Analysis: Explain the formation of the white precipitate (BaSO4) in the qualitative analysis with BaCl2. Relate this to the presence of sulfate ions in alum.

In conclusion, the synthesis and analysis of alum provide valuable insights into the principles of stoichiometry, chemical reactions, and qualitative analysis techniques. The calculated molar mass, theoretical yield, and percent yield offer quantitative measures of the success of the synthesis, while flame tests and qualitative analysis enhance our understanding of the composition of the synthesized alum. This lab not only reinforces fundamental chemical concepts but also demonstrates practical applications of alum in various industries.

This experiment delves into the intriguing chemistry of aluminum and its compounds. Aluminum metal displays reactivity with both strong acids and strong bases, forming aluminum hydroxide, an amphoteric substance that dissolves in both acids and bases. The synthesis of alum, a double sulfate salt, will be performed in this experiment, followed by the determination of its theoretical and percent yield. Analytical techniques will be employed to assess the purity of the synthesized alum.

Balanced Equations for Synthesis:

1. 2Al+2KOH+6H2O→2K[Al(OH)4]2Al+2KOH+6H2​O→2K[Al(OH)4​]
2. K[Al(OH)4]+6H2SO4→2Al(OH)3+2KHSO4+4H2OK[Al(OH)4​]+6H2​SO4​→2Al(OH)3​+2KHSO4​+4H2​O
3. 2Al(OH)3+6H2SO4→2Al(H2O)63++6HSO4−2Al(OH)3​+6H2​SO4​→2Al(H2​O)63+​+6HSO4−​

Hypothesis:

Before the experiment, the theoretical yield of alum will be determined, and a hypothesis will be formulated regarding which analytical technique will provide the most accurate analysis of the alum.

Procedure: Part A - Synthesis:

1. Weigh 1.000 g of aluminum and cut it into small pieces.
2. Dissolve aluminum in 15.0 ml of 3 M KOH to form aluminate.
3. Filter the solution and add 15.0 ml of 9 M H2SO4 to form solid Aluminum hydroxide.
4. Clear the solution and allow crystallization.
5. Capture crystals using suction filtration and wash with ethanol.
6. Record the room temperature and crystal mass.

Calculations: Part A:

1. Calculate actual yield and percent yield.
2. Adjust the yield considering the solubility of alum in water at room temperature.

Procedure: Part B - Analysis of Properties:

1. Flame test: Test a small amount of crystal in a Bunsen burner flame and record the color.
2. Gravimetric analysis for SO42- anion: React alum with strontium nitrate, filter, and record the mass of the precipitate.
3. Percentage of water in a Hydrate: Heat alum to determine water content.
4. Physical Properties: Record color, shape, and odor of alum. Melt alum and record temperature during recrystallization.

Calculations: Part B:

1. Calculate mass percent of SO42- and water in alum.
2. Calculate theoretical mass percent using a published formula of alum.

Discussion:

1. Discuss the chemical reactions in each step of the alum synthesis.
2. Analyze the calculated yields, considering potential sources of error.
3. Interpret the results of the analytical techniques used for alum purity assessment.

In conclusion, this comprehensive experiment provides insights into the synthesis and analysis of alum, encompassing theoretical and percent yields, flame tests, gravimetric analysis, and determination of water content. The results contribute to understanding the properties of alum and the accuracy of analytical techniques. This experiment bridges theoretical knowledge with practical applications, enhancing the understanding of aluminum chemistry.

Updated: Feb 29, 2024
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Lab: Synthesis and Analysis of Alum. (2024, Feb 29). Retrieved from https://studymoose.com/document/lab-synthesis-and-analysis-of-alum

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