1. Indicators and pH
Objective:
To learn about pH and how indicators show a substance to be an acid or a base.

2. Research: Acid: solutions – high concentration of H3O+ ions. Hydronium
Base: solutions – high concentration of OH- ions. Hydroxyl
pH: percent of hydrogen – how acidic it is.

3. pH scale: series of numbers 0-14. 7= neutral, 0-6 acid, 8-14 base.
Indicator: substance that shows a definite color change when mixed with acid or base.

4. Effect on Acids Effect on Bases
Blue litmus paper: pink ___
Red litmus paper: ___ blue
Phenolphthalein: stays clear shocking pink
Bromthymol blue: orange ___
Congo red: blue ___
As the pH of a solution changes, the indicator shows a specific color change.

5. Procedure I – Acid After each step, record your observations.
Drop a small drop of HCl onto blue litmus paper.
Drop a small drop of HCl onto red litmus paper.
Place a small amount of HCl into test tube A. Add 1 drop of phenolphthalein. Rinse TT.
Place a small amount of HCl into test tube A. Add 2 drops of bromthymol blue. Rinse TT.
Place a small amount of HCl into test tube A. Add 1 drop of congo red. Rinse TT.

6. Procedure II – Base After each step, record your observations.
Drop a small drop of NaOH onto blue litmus paper.
Drop a small drop of NaOH onto red litmus paper.
Place a small amount of NaOH into test tube B. Add 1 drop of phenolphthalein. Rinse TT.
Place a small amount of NaOH into test tube B. Add 1 drop of bromthymol blue. Rinse TT.
Place a small amount of NaOH into test tube B. Add 1 drop of congo red. Rinse TT.

7. Reaction with
Acid
Base
Blue litmus paper
Red litmus paper
Phenolphthalein
Bromthymol blue
Congo red