Investigating pH of common household substances
Students investigate the pH level of household substances by testing a variety of common compounds. Substances are tested with pH strips and placed on the continuum of the pH scale range of 1 to 14. After testing a solution, the student compares the strip color to the scale provided on the container and gives the solution a rating from 1-14. Using the determined number, the name of the solution is placed on the continuum. Students will find that household substances have a specific pH property which is a characteristic needed for the substance's use. Following the lab, students will be assigned the task of testing other substances in their home to determine the pH of those substances.
Identify acids and bases by using the pH scale. Explain differences between strong acids and bases, and weak acids and bases.
Identify uses of acid and base liquids.
Vocabulary: pH scale, acid, acidity, base, basicity, neutral, neutralization indicator
Context for Use
Resource Type: Activities:Lab Activity
Grade Level: Middle (6-8)
Description and Teaching Materials
Materials for a class of 30 students:
pH strips which indicate an acid-base range from 1-14
15 common household substances in liquid form
- Mountain Dew
- distilled water
- glass cleaner with ammonia
- lemon juice
- human saliva
- orange juice
- apple juice
15 plastic cups
30 Q-tip swabs
15 eye droppers, optional
water, for clean-up and safety procedure
sink with drain or plastic lined disposal container
30 lab data forms
1. Label a cup with each for the liquids to be tested
2. Fill cup approximately ½ full with liquid
3. Arrange liquids to be tested at 14 stations
4. At saliva testing station, provide a Q-tip swab for each student and a container for disposal of used swab and testing strip.
5. Provide paper toweling at each station
6. Place one eye dropper at each station if using
Student preparation and procedure:
1. If guided activity, review properties of acids and bases; and the uses of each. Discuss characteristics of acids - sour, corrosive, etc.; and bases - bitter, slippery, etc. Acids are used to break down other substances and react chemically with metals. Bases are used for cleaning and react to neutralize acids.
2. Assign students a lab partner and place students in groups of 2.
3. Explain procedure. Each group will be assigned a station and when told will move to the next moving from lower to higher numbered station. The group at station 15 moves to station 1 and continues on to high numbered station. Students are to complete 15 stations.
4. Give specific directions for the saliva test. Each student is to test their own saliva by swabbing the inside of their mouth with a clean Q-tip and test it by touching the Q-tip to an un-used pH testing strip. Discard Q-tip and used strip in container provided at that station.
5. Give each student a lab sheet to record the test result of each substance. Explain that they are to write name of liquid next to the number which corresponds to the tested result.
6. Provide each group a pH color testing guide and 15 sections of pH testing strip.
7. Begin the activity. Allow 2-3 minutes per station. Adjust number of stations for shorter class periods.
8. Conclude with students cleaning up the station at which they finish.
9. Dispose of acids and bases in separate containers or at separate sinks.
10. Students analyze data by comparing the similarities and differences of liquids next to each other on the scale and those which are farther apart. Example: 2 to 3, 4 to 5, 7 to 8, 10 to 11; and 2 to 10, 4 to 9.
11. Discuss uses of liquids 1-6 and liquids 8-14.
12. Explain the characteristics of liquids which tested 7.
13. Students record observations and discussion notes on reverse of lab sheet.
14. Lab report is graded for completion, accuracy of test results and thought process.
Homework: Students receive a second lab sheet and a length of pH testing strip with scale. They are to test a minimum of four additional and different liquids in their home and record the pH of each.
Teaching Notes and Tips
Previous to teaching with this activity, acids and bases were taught with overheads, large pH scale and reading the textbook. On occasion liquids were tested simply for acidity or basicity, which did not show the continuum of pH nor allow comparisons.
6.II.B. 2 - Chemically different properties