University of Virginia
Physics Department

## Where Does My pH Rank?

A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.2

Objectives

Students will:

• Determine the pH of various substances using Hydrion Paper and a pH meter;
• Arrange, in order from strongest to weakest, acidic substances and basic substances.

Background Information

An indicator such as Hydrion Paper contains a chemical which changes color when it reacts by coming into contact with an acid or a base substance. Hydrion Paper is often called pH paper (pH means Power of Hydrogen) because it contains universal indicator which changes to a different color for every pH. The advantage of this indicator is that the exact pH of a solution can be determined. The pH scale is a logarithmic relationship. Each number of the scale differs from the next by a factor of ten. For example, an acid with a pH of 3 is ten times more acidic than an acid with a pH 4. A base with a pH of 10 is ten times more basic than a base with a pH of 9. The pH scale ranges from 0 to 14. A substance having a pH of 7 is neutral. Acids have a pH less than 7. The lower the number, the stronger the acid. Bases have a pH higher than 7. The higher the number, the stronger the base.

### Student Activity

Materials (per group)

• 1 roll of Hydrion Paper
• pH meter
• Egg Whites
• Banana
• 100 mL Apple Juice
• 100 mL Vinegar
• 100 mL milk of magnesia (Mg(OH))
• Lemon
• bar of soap
• shampoo
• ammonia
• 100 mL lye or NaOH or drain cleaner
• 100 mL distilled water
• 100 mL salt water with a little baking soda added

Procedure

1. Find the pH for each substance using Hydrion paper and the pH meter as needed and record that value under the picture of that substance.
2. Color, cut out the picture, and glue it on the pH scale sheet in the correct location.

Students with Special Needs

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Assessment

1. Is vinegar an acid or base?
1. Acid
2. Base
3. Neutral
2. Which of the following is a stronger acid than apple juice?
1. Ammonia
2. Egg White
3. Banana Pulp
4. Lemon Juice
3. Which pH is that of a strong acid?
1. 2
2. 5
3. 8
4. 12
4. Which pH is that of a strong base?
1. 2
2. 5
3. 8
4. 12
5. Which of the following food substances is basic?
1. Lemon Juice
2. Apple Juice
3. Banana Pulp
4. Egg White
6. Which substance is neutral?
1. Shampoo
2. Tap Water
3. Egg White
4. Ocean Water
7. What is the strongest acid?
1. Lemon Juice
2. NaOH
3. Tap Water
4. Ammonia
8. What is the approximate pH of soap?
1. 3
2. 5.52
3. 9
4. 13.5
9. Which of the following has a pH between apple juice and seven? (Which substance is slightly weaker than apple juice?)
1. Vinegar
2. Banana Pulp
3. Soap
4. Lemon Juice
10. Which has the weakest pH value? (The pH which is most near seven?)
1. Lemon Juice
2. NaOH
3. Ocean Water
4. Ammonia