LAB: ACIDS, BASES, AND THE pH SCALE
Pre-Lab Discussion:
What is an acid? Provide some examples.
What is a base? Provide some examples.
What is an indicator? What does it tell you about solutions?
What is the pH scale? Why/How is it used?
Hypothesis: Predict where the selected solutions will fall on the pH scale below. Draw
an arrow and select a number that you think is appropriate for each solution.
1 - Distilled water
2 - Tap water
3 - Vinegar(Acetic acid)
4 - Baking soda and tap water
5 - *0.5 M NaOH
6 - Apple Juice
11 - Lemon Juice
7 - *Ammonia
12 - Sprite
8 - *Bleach
13 - ______________
9 - alka seltzer and tap water
10 - dish soap and tap water
*use extreme caution when handling this solution
1 -------------------------------------------------- 7 ------------------------------------------------- 14
Materials:
Micro well trays (2)
Cabbage juice indicator
pH paper and scale
Various household chemicals
Prepared acids and bases
Pipettes
Glass stirring rods
Deionized water
Procedure:
1. Add 5 drops of each of the selected solutions to each of the wells starting at “1”
and moving clockwise around one of the trays. Be sure to keep track of which
solution is placed in each well.
2. Add 5 drops of cabbage juice indicator to each of the wells and observe the color
change. Decide on the proper order of solutions from most acidic to most basic.
The spectrum produced by cabbage juice indicator goes from red (most acidic)
>>>red>>> pink >>> purple(neutral) >>> blue >>> green >>> yellow >>>
(most basic). .
3. Collect three long strips (10 cm each) of orange pH paper and place them on a
paper towel. Try to hold this paper on the ends as the oils in your hands can
influence your results.
4. Dip a glass stirring rod into each well, one at a time, and place it on the pH paper.
Be sure to dip your stirring rod in the deionized water between each test to
avoid error or contamination of your solutions.
5. Observe the color change and assign each solution a number based on the pH
color chart on the front screen.
6. After compiling your data, complete the pH scale below with any corrections you
need to make. Be sure to include specific numbers for each solution you tested.
Final Results
1 -------------------------------------------------- 7 ------------------------------------------------- 14