TITLE: Determining Acids and Bases
AUTHOR: Melodie Hill, Lewis©Arriola Elem., CO
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
ACTIVITY: (Can be Lab or Demo)
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 1. 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.
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