Lab: Acids and Bases
Part A: pH of Mystery Substances
Purpose:
The purpose of this lab is to determine the pH of a variety of unknown substances
using pH indicator paper and identifying their common names.
Procedure:
1. Using a spot plate, add a few drops of each substance to different wells (make sure you know
which goes into what).
2. Using forceps, dip one small piece of pH indicator paper into a well. Using the chart given on
the plastic tube, identify its pH and whether it’s an acid, base or neutral substance. Record
your observations on the chart.
3. Calculate the concentration of hydrogen ions, [H+] based on your experimental pH value.
Record your calculations on the chart.
4. Record your pH values for each substance on the pH scale diagram.
5. Determine the names of the substances using your knowledge of pH, acids and bases. Write
down your guesses on the chart.
Observations:
Substance
A
B
C
D
E
F
pH
Acid, Base or
Neutral?
[H+] (mol/L)
Common Name
Part B: Identification of Acids and Bases
Purpose:
In this activity, you will be given six unknown solutions. Using four different
tests, you will determine whether the substances are acidic, basic or neutral.
Materials:
o Five mystery solutions
o Test tubes and test tube rack
o Phenolphthalein indicator
o Magnesium metal pieces
o
o
o
o
Baking soda (NaHCO3)
Red and blue litmus paper
Stirring rod
Scoopula
Safety: You are working with chemicals. Do not get anything on your skin or clothing. If spills
occur, wash immediately with cold water and notify your teacher. Always wear safety goggles.
Procedure:
1. Using a dropper, fill three test tubes with Solution A, putting approximately 5 mL in each.
This is the width of your thumb (approximately 3 cm high).
2. With a stirring rod, place one drop of the solution on a piece of red litmus paper and another
drop on a piece of blue litmus paper.
3. In the first test tube, add two drops of phenolphthalein.
4. In the second test tube, add a small piece of magnesium metal.
5. In the third test tube, using a scoopula, add a small amount of baking soda.
6. Record your observations in the chart (see Observations section to read instructions).
7. Dispose the contents of the test tubes in the waste bin (do not put it down the sink) and
completely wash all three test tubes.
8. Repeat steps 1-7 using the other 4 solutions (Solutions B, C, D, and E).
Observations:
Fill in the table on the next page to indicate how each solution reacts with each test.
o For the acid-base indicators (red/blue litmus paper and phenolphthalein), note any colour
changes
o For magnesium metal, is there a reaction? If so, what happened?
o For baking soda (NaHCO3), is there a reaction? If so, what happened?
Discussion:
On the chart, state whether each substance is acidic, basic or neutral. What observations did you
make to conclude that?
Part C: Acid-Base Reactions
A) Magnesium and HCl
Procedure:
1. Fill a clean, dry test tube with 10 mL HCl solution (width of two thumbs). Add a piece of
magnesium metal.
2. Light a wooden splint and bring it close to the mouth of the test tube. Do NOT drop the splint
in the test tube. Record your observations below:
Observations:
Discussion (on a separate piece of paper):
1. Write the word AND balanced chemical equation for this reaction.
2. What kind of reaction is this?
3. What did you observe when the lighted splint was placed at the mouth of the test tube? What
does your observation tell you about one of the products of the chemical reaction?
B) Aluminum and NaOH
Procedure:
1. Add a few pieces of aluminum to the bottom of a clean, dry test tube. Add enough NaOH
solution to cover the aluminum pieces. Do not waste the NaOH solution!
2. Gently shake the test tube. Feel the test tube and observe the contents.
3. If a gas is produced in step 2, test the gas with a lighted splint near the mouth of the test tube.
4. Record your observations below:
Observations:
Discussion (on a separate piece of paper):
1. Write the word AND balanced chemical equation for this reaction.
2. What kind of reaction is this?
3. The chemical reaction between aluminum and a basic solution is the same reaction that is
used to open a plugged (clogged) drain. Commercial drain cleaners are a mixture of
aluminum and sodium hydroxide. Explain why this chemical reaction can clear a drain that is
clogged with fat.