1. Use your observations to group the test solutions into as many categories as are needed to account for similarities and differences in chemical reactivity. Be prepared to justify your classification scheme.
   
2. For those solutions that indicated high conductivity with the tester, identify the ions present in solution.
   
3. Hydrochloric acid is a member of a class of compounds called acids. Sodium hydroxide is a member of a class of compounds called bases. What other substances in the group of seven tested should be called acids or bases?

Part I Implications and Applications

1. What strategy could you use to identify an unknown substance as an acid or a base?
   
2. A drop of bromthymol blue placed in an unknown solution turns yellow. Is the solution acidic or basic?
   
3. Why do you think universal indicator is called an indicator?
   
4. What ionic species is common among the group of compounds you categorized as acids? As bases?
   

Part II Procedure

1. Add 20 drops 0.1 M HCl to the first well or tube.
   
2. Remove two drops and place them in the second tube or well. Add 18 drops of water to the second tube or well, and mix.
   
3. Take two drops of the second solution and add them to the third well. Add 18 drops of water to the third well and mix.
   
4. Continue this "serial dilution" until you have five increasingly-dilute solutions of hydrochloric acid, HCl, as shown in the diagram below.

5. Repeat Steps 1 through 4, starting with 0.1 M sodium hydroxide, NaOH, rather than hydrochloric acid.

6. Add one drop of universal indicator to each well or tube. Record your observations. (See sample Data Table.) .

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Figure 9. Sample Data Table.

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