Reactions - Qualitative Determination of Unknowns
Objective
1. Determine the identity of unknowns using qualitative means
2. Independently write a lab procedure given general guidance
Discussion
You will be given four solid unknowns, labeled A, B, C and D. The likely chemical names of these
unknowns are: sodium carbonate, magnesium sulfate, sodium chloride and calcium carbonate. In
addition to these solids, water, an acid and a basic solution will be made available to you. Based upon
your observations of the reactions of the four unknown solids, you must determine their identity and
justify your reasoning. In addition, you must provide both balanced formula equations and net ionic
equations for any reaction that occurs.
Pre-Lab Work:
1. Create a procedure and capture it in your lab notebook. You should also include a data table
capturing your qualitative observations. For example:
Water
Acid
NaOH
Unknown A
Unknown B
Unknown C
Unknown D
2. Which of the solids would you expect to be soluble in water?
3. What (if any) precipitates might you expect to observe in this experiment?
Post Lab Work:
1. Identify each of the unknowns and justify your answer.
2. Write balanced formula equations and net ionic equation of each
reaction you observed.
3. When salts dissolve in water, its ions are surrounded in solution by
water molecules (an ion-dipole attraction as shown in the figure to the
right.) For the following reaction in a one-liter beaker: 0.1 mol of
magnesium sulfate plus 0.1 mol of barium chloride produces barium
sulfate plus magnesium sulfate.
a. Write the formula equation and then next ionic equation.
b. Draw a beaker and show the major species (ions, molecules or solids) present after the
reaction is completed. Include at least two waters of hydration (water molecules) around
each ion in solution.
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