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AP Chemistry
Unit 8: Acids and Bases
8.5 pH and <latex>pK_a</latex>
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The pH scale ranges from 0 to
14
A solution with a
pH
greater than 7 is basic.
True
A pH less than 7 indicates an
acidic
What does a lower
p
K
a
pK_{a}
p
K
a
value indicate?
Stronger acid
Lower
p
K
a
pK_{a}
p
K
a
values correspond to stronger acids.
True
The pH scale is defined as the negative logarithm of the hydrogen ion
concentration
Order the following pH ranges from most acidic to most basic:
1️⃣ 0-6.9
2️⃣ 7
3️⃣ 7.1-14
Match each acid with its
p
K
a
pK_{a}
p
K
a
value:
Hydrochloric Acid (HCl) ↔️ -6.0
Acetic Acid (
C
H
3
C
O
O
H
CH_{3}COOH
C
H
3
COO
H
) ↔️ 4.74
Hydrocyanic Acid (HCN) ↔️ 9.31
When
[
A
−
]
=
[A^{ - }] =
[
A
−
]
=
[
H
A
]
[HA]
[
H
A
]
, the pH equals the
p
K
a
pK_{a}
p
K
a
.
True
p
H
=
pH =
p
H
=
p
K
a
+
pK_{a} +
p
K
a
+
log
[
A
−
]
[
H
A
]
\log \frac{[A^{ - }]}{[HA]}
lo
g
[
H
A
]
[
A
−
]
is the formula for the Henderson-Hasselbalch equationpH
What does the pH symbol represent in the Henderson-Hasselbalch equation?
Negative logarithm of hydrogen ion concentration
What does a pH of 7 indicate about a solution?
Neutrality
As the hydrogen ion concentration increases, the
pH
decreases, indicating a more acidic solution.
True
Match the acid with its strength:
Hydrochloric Acid (HCl) ↔️ Very Strong
Acetic Acid (CH_3COOH) ↔️ Weak
Hydrocyanic Acid (HCN) ↔️ Very Weak
A
pH
of 7 indicates neutrality.
True
What is the formula for calculating pH from hydrogen ion concentration?
p
H
=
pH =
p
H
=
−
log
10
[
H
+
]
- \log_{10}[H^ + ]
−
lo
g
10
[
H
+
]
What is
p
K
a
pK_{a}
p
K
a
?
Acid strength indicator
pH is defined as the negative logarithm of the hydrogen ion
concentration
Match each acid with its
p
K
a
pK_{a}
p
K
a
value:
Hydrochloric Acid (HCl) ↔️ -6.0
Acetic Acid (
C
H
3
C
O
O
H
CH_{3}COOH
C
H
3
COO
H
) ↔️ 4.74
Hydrocyanic Acid (HCN) ↔️ 9.31
A pH value less than 7 indicates an acidic solution.
True
What is the formula for calculating
p
K
a
pK_{a}
p
K
a
?
p
K
a
=
pK_{a} =
p
K
a
=
−
log
10
(
K
a
)
- \log_{10}(K_{a})
−
lo
g
10
(
K
a
)
The relationship between
p
K
a
pK_{a}
p
K
a
and acid strength is inverse
Match each component of the Henderson-Hasselbalch equation with its description:
pH ↔️ Negative logarithm of hydrogen ion concentration
p
K
a
pK_{a}
p
K
a
↔️ Negative logarithm of acid dissociation constant
Conjugate Base Concentration ↔️
[
A
−
]
[A^{ - }]
[
A
−
]
Acid Concentration ↔️
[
H
A
]
[HA]
[
H
A
]
Match the symbol with its description:
p
K
a
pK_{a}
p
K
a
↔️ Negative logarithm of the acid dissociation constant
[
A
−
]
[A^{ - }]
[
A
−
]
↔️ Conjugate base concentration
[
H
A
]
[HA]
[
H
A
]
↔️ Acid concentration
pH is defined as the negative logarithm of the hydrogen ion
concentration
What is the pH of a solution with
[
H
+
]
=
[H^ + ] =
[
H
+
]
=
1
×
1
0
−
3
1 \times 10^{ - 3}
1
×
1
0
−
3
M?
3
What is the
p
K
a
pK_{a}
p
K
a
defined as?
Negative logarithm of
K
a
K_{a}
K
a
The relationship between
p
K
a
pK_{a}
p
K
a
and acid strength is direct.
False
As
p
K
a
pK_{a}
p
K
a
decreases, the acid strength increases
What is the
p
K
a
pK_{a}
p
K
a
of acetic acid (
C
H
3
C
O
O
H
CH_{3}COOH
C
H
3
COO
H
)?
4.74
What does pH measure?
Acidity or basicity
A solution with a pH less than 7 is considered
acidic
The pH scale ranges from 0 to
14
.
True
The formula for
p
K
a
pK_{a}
p
K
a
is pK_{a} = - \log_{10}(K_{a})</latex>.
True
What is the formula for
p
K
a
pK_{a}
p
K
a
?
p
K
a
=
pK_{a} =
p
K
a
=
−
log
10
(
K
a
)
- \log_{10}(K_{a})
−
lo
g
10
(
K
a
)
What happens to acid strength as
p
K
a
pK_{a}
p
K
a
decreases?
Acid strength increases
What pH value indicates a neutral solution?
7
A lower
p
K
a
pK_{a}
p
K
a
value indicates a stronger acid.
True
What is the Henderson-Hasselbalch equation for weak acids?
p
H
=
pH =
p
H
=
p
K
a
+
pK_{a} +
p
K
a
+
log
[
A
−
]
[
H
A
]
\log \frac{[A^{ - }]}{[HA]}
lo
g
[
H
A
]
[
A
−
]
What equation is used to calculate the pH of weak acids?
Henderson-Hasselbalch equation
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