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The Synthesis of Alum


The term alum is a general family name for a crystalline substance composed of cations with 1+ and 3+ charges. In this experiment, you will synthesize a type of alum called potassium aluminum sulfate dodecahydrate, KAl(SO4)2•12H2O. You will synthesize this compound by placing the appropriate ions in one container in aqueous solution and then evaporate the water to form the alum crystals.

This particular compound has been chosen because it is relatively simple to prepare a pure sample. The process of synthesizing this compound is interesting in that it involves both chemical and physical reactions. Chemically, aluminum is oxidized from aluminum foil to prepare the Al3+ ions. Physically, as the solution that contains the mixture of ions evaporates, crystals will form which contain six waters of hydration bonded to the aluminum ion and six waters bonded to the potassium ion.

Aluminum is considered a reactive metal, but because its surface is usually protected by a thin film of aluminum oxide, it reacts slowly with acids. It does, however, dissolve quickly in basic solutions. Excess hydroxide ion converts the aluminum to the tetrahydroxoaluminate (III) ion, [Al(OH)4]-, and a slow addition of acid will precipitate the white, gelatinous aluminum hydroxide, Al(OH)3. Continued addition of acid causes the hydroxide ions to be completely neutralized, and the aluminum exists in solution as the hydrated ion [Al(H2O)6]3+. Aluminum hydroxide is considered to be an amphoteric hydroxide because it dissolves in both acids and bases.


In this experiment, you will

  • Synthesize a sample of potassium aluminum sulfate dodecahydrate (alum).
  • Observe and record the process of synthesizing a compound.
  • Calculate the percent yield of your synthesis.

Sensors and Equipment

This experiment features the following Vernier sensors and equipment.

Option 1

Option 2

Additional Requirements

You may also need an interface and software for data collection. What do I need for data collection?

Standards Correlations

See all standards correlations for Advanced Chemistry with Vernier »

Advanced Chemistry with Vernier

See other experiments from the lab book.

1The Determination of a Chemical Formula
2The Determination of the Percent Water in a Compound
3The Molar Mass of a Volatile Liquid
4Using Freezing-Point Depression to Find Molecular Weight
5The Molar Volume of a Gas
6Standardizing a Solution of Sodium Hydroxide
7Acid-Base Titration
8An Oxidation-Reduction Titration: The Reaction of Fe2+ and Ce4+
9Determining the Mole Ratios in a Chemical Reaction
10The Determination of an Equilibrium Constant
11Investigating Indicators
12The Decomposition of Hydrogen Peroxide
13Determining the Enthalpy of a Chemical Reaction
14ASeparation and Qualitative Analysis of Cations
14BSeparation and Qualitative Analysis of Anions
15AThe Synthesis of Alum
15BThe Analysis of Alum
16Conductimetric Titration and Gravimetric Determination of a Precipitate
17Determining the Concentration of a Solution: Beer's Law
18Liquid Chromatography
20Electrochemistry: Voltaic Cells
22The Synthesis and Analysis of Aspirin
23Determining the Ksp of Calcium Hydroxide
24Determining Ka by the Half-Titration of a Weak Acid
25The Rate and Order of a Chemical Reaction
26The Enthalpy of Neutralization of Phosphoric Acid
27α, β, and γ
28Radiation Shielding
29The Base Hydrolysis of Ethyl Acetate
30Exploring the Properties of Gases
31Determining Avogadro's Number
32Potentiometric Titration of Hydrogen Peroxide
33Determining the Half-Life of an Isotope
34Vapor Pressure and Heat of Vaporization
35Rate Determination and Activation Energy

Experiment 15A from Advanced Chemistry with Vernier Lab Book

<i>Advanced Chemistry with Vernier</i> book cover

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Dev Reference: VST0015

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