Grade 10 Applied Science – Unit Chemistry
Chemical Reactions – Acid-Base Rainbow
The pH scale is used to rank the reactivity of acids and bases. In acids, pH represents the number of H +
ions that are in a solution. For bases, it represents the number of H+ (or OH-). One step (e.g., pH = 1 to
pH = 2) represents 10X reduction in the acidity of the solution or 10X less reactive than the other.
In this activity you will be asked to prepare several successively less concentrated solution of either an
acids or a base (acids: pH = 1 to pH = 6; Bases: pH = 13 to pH 8). You will also try to identify the pH
range of other common substances.
Hypothesis – What do you think will happen?
Materials
 6 - 20 mL test tubes
 20 mL NaOH
 20 mL HCl
 Medicine droppers
 Test tube rack
 Universal Indicator
 10 mL Graduated cylinder
 10 mL H2O
 Pipette
Methods
1. Fill a graduated cylinder with 6 mL of H2O (be precise).
2. Put 5 mL of H2O solution into a test tube. Keep the remaining 1 mL H2O in the cylinder
3. Put 5 mL of HCl solution in a test tube and place it on a test tube rack
4. Add 9 mL HCl to the 1 mL H2O. (You should have a 10 mL solution of HCl-H2O)
5. Measure and put 5 mL of this solution in a test tube and place on a rack.
6. Measure and put 1 mL of HCl-H2O solution into a test tube
7. Add 1 mL H2O to the remaining 4 mL HCl-H2O solution
8. Measure and combine 5 mL HCl to 5 mL H2O
9. Add a few drops of universal indicator to each of the solutions.
10. Observe changes and differences.
11. Rinse your test tubes with tap water and repeat all steps using NaOH
Analysis
1. What happened to the universal indicator after it was mixed with the solutions. Were there any
differences among the solutions?
2. The following is a pH scale diagram. Answer the questions relating to the diagram.
1
2
3

From the diagram above, a solution that has a pH in the within the range of described by “1” is an
acid / base. A solution that has a pH range described by “2” an acid / base. A solution that has a
pH described by “3” considered _________________ because it has same number of H+ as OHions.

Label on the pH scale diagram, the position (by pH) of the following substances. Pure (distilled)
water, ammonia (windex), drano (drain opener), lemon juice, apples and antacids
Table 1. Results from adding Universal Indicator to different concentrations of HCl-H2O solution
Solution Concentration
Volume of
Universal
Indicator
Added
(mL)
Observations
5 mL 100% H2O
5mL 100% HCl
5 mL 50% HCl
5 mL 50% H2O
4.5 mL 90% HCl
0.5 mL 10% H2O
3.5 mL 75% HCl
1.5 mL 25% H2O
Table 1. Results from adding Universal Indicator to different concentrations of NaOH-H2O solution
Solution Concentration
5 mL 100% H2O
5mL 100% NaOH
5 mL 50% NaOH
5 mL 50% H2O
4.5 mL 90% NaOH
0.5 mL 10% H2O
3.5 mL 75% NaOH
1.5 mL 25% H2O
Volume of
Universal
Indicator
Added
(mL)
Observations