Adv Chem Lab Report #9

Synthesis of Alum
Advanced Chemistry Lab #9
Purpose: ( brief statement of what you are attempting to do. These are similar to the
objectives. )
Procedure: (A brief description of the method you are using. You may refer to the lab
document for specific instructions, but you should include a brief statement of the
method. DO not include lengthy, detailed directions. A person who understands
chemistry should be able to read this section and know what you are doing. Include all
chemicals used and the major equipment. )
Observations: (General descriptions of visible appearances or changes that occur
during the experiment, such as “table salt is a white, cube-shaped crystal which dissolves
in water. (Qualitative))
Data: (Neatly arranged measured values listed in tabular form. The units of
measurement MUST be included with the numerical values. The accuracy of the
measurement can also be included as a range (+/-). Calculated answers that are derived
by performing a simple mathematical operation can also be included in the data table. If
the graphs are included, make the graphs an appropriate size. Label all axes and give
each graph a title.)
Calculations: (Show all calculations with formula and appropriate units on all numbers.
Neatly demonstrate the math set-ups, including units. Label what is being calculated. –
make it organized. Show error calculations where appropriate. If experiments are
qualitative, this section may be omitted.)
Conclusion: (Make a simple statement concerning what you can conclude form the
experiment. Refer back to the purpose of the lab to write this section. (i.e. How was the
purpose of the experiment fulfilled?))
Discussion of Theory: (In this section you should include such information as: What
theory was demonstrated in this experiment (Include concepts used in the experiment)?
What do the calculations show? Why does (or doesn’t) the experiment work? This
section shows me that you understand the concepts used in the lab. Be detailed and ask if
you need help! )
Experimental Sources of Error: (What are some specific sources of error, and how do
they influence the data? Do they make the values obtained larger or smaller than they
should be? Which measurement was the least precise? Instrumental error and human
error exist in all experiments, and should not be mentioned as a source of error unless
they caused a significant fault. Significant digits and mistakes in calculations are NOT a
valid source of error. In writing this section it is sometimes helpful to ask yourself what
you would do differently if you were to repeat the experiment and wanted to obtain better
precision. If you can calculate percent error, do so and include in this section. )
Post Lab Questions: (Answer any questions included in the lab. Answer in such a way
that the meaning of the question is obvious in your answer. )
1. Determine the theoretical yield of the alum. Use the aluminum foil as the limiting
reagent and presume that the foil was pure aluminum.
2. Calculate the percent yield of your alum crystals.
3. Discuss the factors that affected the percent yield.
4. Write the balanced net ionic equations for the following: (a) aluminum and potassium
hydroxide, yielding [Al(OH)4] – and hydrogen gas; (b) hydrogen ions and [Al(OH)4] –,
yielding aluminum hydroxide; (c) aluminum hydroxide and hydrogen ions, yielding
[Al(H2O)6]3+; and (d) the formation of alum from potassium ions, sulfate ions,
[Al(H2O)6]3+, and water.
5. Describe a synthesis reaction.
6. Describe how the solubility of alum in various solvents and water at different
temperatures was used in conducting the experiment.
7. Write a detailed description of the alum crystals.