In this Acid and Base identification and neutralisation reaction, what would be the independent, dependent and controlled variables?

Question

1. Place 5ml of unknown “A” into a test tube and place in the test tube rack.

2. Place 5 drops of universal indicator into unknown “A”.

3. Observe the colour change and using the pH scale determine the pH and if the solution is an acidic, basic or neutral.

4. Complete the same process for unknown “B” as per steps 2 and 3 and determine if the unknown “B” is acidic, basic or neutral.

5. Record results and observations in a table 6. Add the acid to the base and observe the colour change. Using the pH scale determine if neutralised solution is acidic, basic or neutral.

Answer 1

This is not a typical experiment in the sense that there really is no well defined control, but be that as it may, it seems that the dependent variable would be the pH, since that is dependent on the H+ concentration.  The independent variable would be the nature of the solution, i.e. an acid or a base which does not vary. A proper control would have been a known acid and a known base to prove that the indicator is operating as expected.