Determining Acids and Bases

AUTHOR: Melodie Hill, Lewis©Arriola Elem., CO

May 1994

These lesson plans are the result of the work of the teachers who have attended the Columbia Education Center's Summer Workshop. CEC is a consortium of teacher from 14 western states dedicated to improving the quality of education in the rural, western, United States, and particularly the quality of math and science Education. CEC uses Big Sky Telegraph as the hub of their telecommunications network that allows the participating teachers to stay in contact with their trainers and peers that they have met at the Workshops.

GRADE LEVEL/SUBJECT: intermediate, science

OVERVIEW: An introduction to using indicators to determine acids and bases.

PURPOSE: To introduce acidity/alkalinity of substances using an indicator to determine their differences and safety precautions in handling of each.

OBJECTIVES: The student will use purple cabbage indicator to test five know substances for acidic/alkaline balance. The student will discuss the safety precautions required both inside and outside a lab in handling acids and bases. RESOURCES/MATERIALS:

1. Several clear containers
2. Several household substances (see activity 2)
3. Purple Cabbage Indicator (Coarsely shred a head of purple cabbage. Place in saucepan and fill 1/2 full of water. Boil about ten minutes. Strain the liquid and refrigerate until ready to use.)
4. spoons, paper towels, safety glasses

Label 4 clear containers with numbers 1 - 4. Fill each 1/2 way with water, white vinegar, ammonia and corn syrup. Have students note color, smell, etc. Do Not Taste. Drop a paper clip in each to discuss density and clue to the identity of corn syrup. Add 1 teas. purple cabbage indicator to each substance. Note color changes.

vinegar - red - acid
ammonia - green - base
water - purple - neutral

Have students start a chart to record their findings.

ACTIVITY: Have students bring in some of their own to test. Some good examples are lemon juice, Isopropyl, shampoo, peroxide, window cleaner, milk, 7-up, aspirin, antacids, milk of magnesia, tea, orange juice, coke, coffee, detergent. Repeat procedure from activity. Add these findings to yesterdays chart.

ACTIVITY: Make your own indicator paper by soaking paper towels or coffee filters(white) in purple cabbage juice. Let dry and cut into strips. Students can take them home for homework. Dip into substance. Watch for color change. Let dry and mount on 3" x 5" index cards for bulletin board displays.

TYING IT ALL TOGETHER: Discuss and make a chart of acids, bases and neutrals. Identify the potential harm acids and bases can create. Add safety procedures to your chart of acids and bases. Do Not Ingest and Do Not Mix are critical here.