Chem 106 / Dr. Rusay
Adapted from Workshop Chemistry
Names: ___________________________________________
Acids – Bases: pH
Lab & Worksheet
Simulations: https://phet.colorado.edu/sims/html/ph-scale/latest/ph-scale_en.html
On-line questions & submission form:
https://docs.google.com/forms/d/e/1FAIpQLSfte7lj_sKK6ixJiZskBBicsZih9FkQ28NaBEg6W4QSPWATHw/viewform
Reference & Tutorial: https://groups.chem.ubc.ca/courseware/pH/index.html
Characterization of acids and bases by taste is obviously risky and is not a sound experimental approach.
A better method is to use acid–base indicators, which change color based on the acidity or basicity of a
solution. The earliest known acid–base indicators were plant extracts of violets or lilacs. These indicators
were later absorbed onto paper and dried to yield indicator papers. Among the most common of modern
indicator papers are red and blue litmus paper. Red litmus turns blue in basic solution and blue litmus
turns red in acidic solution. The following table includes acids, bases, and neutral solutions of some
common substances. The two litmus columns and the last column are to be completed by using red and
blue litmus paper to test each solution, except for the biological samples, (saliva, blood, & vomit), which
have the test data provided.
Improving upon the capabilities of indicator paper, pH meters are able to quantitatively measure the
acidity of a solution. The samples in the table will be tested with a pH meter by Dr. R. as a demonstration
and the data recorded by you in the table. Stomach acid and drain cleaner are given as examples.
Organize into a group of 3 or 4. Use litmus paper and complete the following table. Assume solutions are
~ 0.1 M. Under the Description column choose: acid, base or neutral.
A
B
C
D
HCl(aq)
stomach acid
NaOH(aq)
drain cleaner
H2O(l)
deionized water
H2O(l) + CO2(aq)
carbonated water
(Seltzer)
E
Na2CO3(aq)
F
NaOCl(aq)
G
CH3COOH(aq)
baking soda
bleach
vinegar
NaCl(aq)
H
I
CH3
salt solution
COO–, Na+(aq)
salt solution
Red
Litmus
Blue
Litmus
red
red
1.0
acid
blue
blue
13.0
base
Solution pH Description
Acid Base Fundamentals
J
K
NH4Cl(aq)
ammonium chloride
NH3(aq)
ammonia
(household cleaner)
L
Mg(OH) 2
Milk of Magnesia
M
Orange juice
N
Milk
O
Saliva (spit) and blood
blue
blue
7.4
P
Vomit
red
red
2.0
Q
Buffer (pH 7)
7.0
(BOTH: acid
& base)
1. Rank the acids by its letter in the list from the strongest to the weakest including the given
example.
2. Rank the bases by its letter in the list from the strongest to the weakest including the given
example.
3. Define a buffer:
The pH of a meat eater’s urine is lower than the urine of people eating a vegan diet.
What this means is not fully understood, but some research has related the difference to
age, muscle, and protein.
SEE: https://www.youtube.com/watch?v=wj0FNMlXMpU
Start the video @ 3:27 to see how red cabbage can be used to test the pH of urine.
4. What is the pH range for human urine, including all types of diets? _________
5. For each of the four reactions, classify the reactants as an acid (A) or a base (B) and the
products as the conjugate acid (CA) or conjugate base (CB).
CN– + H2O → HCN + OH–
___ + ___ → ___ + ___
Acid Base Fundamentals
NH3 + HCl → NH4+ + Cl–
___ + ___ → ___ + ___
H2O + HCl → H3O+ + Cl–
___ + ___ → ___ + ___
CH3COOH + OH– → CH3COO – + H2O
___
+ ___ →
___
+ ___
6. Are the anions (conjugate bases) of strong acids: basic, neutral or acidic?
7. Are the anions (conjugate bases) of weak acids: basic, neutral or acidic?
8. Determine the pH for each of the following [H+]:
Molarity
(M)
1.0 × 10–3
0.010
0.00010
1 × 10–7
1.0 × 10–9
0.0000001
1 × 10–12
pH
9. Calculate [H+], [OH–], and pOH for each of the following pH values:
pH
[H+]
[OH–]
pOH
2
5
7
9
12
Acid Base Fundamentals
10. Model a strong and a weak acid solution. The images on the left are the un-ionized acids.
Draw the respective ionized forms to the right.
Hydroiodic acid, HI, a strong acid:
Hydrofluoric acid, HF, a weak acid, that is 40% ionized:
D
Refer to the following simulations link:
https://phet.colorado.edu/sims/html/ph-scale/latest/ph-scale_en.html
Answer and submit the accompanying on-line questions:
https://docs.google.com/forms/d/1ZlC-Iyv2Pq1FUOn_-ZypL3tMmyJg3XSqBdaF0pKEGJU/viewform
Acid Base Fundamentals
Refer to the following simulation link and answer the accompanying questions:
https://phet.colorado.edu/sims/html/ph-scale/latest/ph-scale_en.html
Using the “Macro” simulation:
1. Consider each substance in the drop box. What is the most acidic substance in this
simulation? _______________ What is its pH value? _____
2. From the drop box, what is the most basic substance in this simulation?
_______________What is its pH value? _____
3. What substance(s) have a pH most similar to that of water (pH 7)? ____________
4. What two substances have the same pH value? ___________________ Briefly explain
why this is plausible.
5. Human vomit has a pH of ~2.0. Is the human stomach an acidic, neutral, or basic
environment? __________ Briefly explain why you think so.
Using the “Micro” simulation:
6. What is the pH of 500. mL of chicken soup?
7. What is the pH of the chicken soup when 500. mL of water is added to it?
8. Briefly explain the reason that the chicken soup’s pH changed when water was added to
it.
9. The pH of an acidic solution will increase, decrease, or stay the same when water (pH 7)
is added? __________
10. The pH of a basic solution will increase, decrease, or stay the same when water (pH 7) is
added? __________
Acid Base Fundamentals
Using the “My Solution” simulation:
11. Complete the following Table.
A
pH
[H+]
[OH–]
pOH
B
C
D
5.8
E
10.2
5.4 x 10-6
2.5 x 10-7
6.6