This document discusses Brønsted–Lowry acids and bases. It defines acids as substances that donate protons and bases as those that accept protons. In water, free protons bond to water molecules to form hydronium ions. Examples are given of hydrochloric acid donating a proton to water, making water the base, and ammonia accepting a proton from water, making water the acid. Conjugate acid-base pairs are defined as the products of acid-base reactions, where the acid forms its conjugate base and the base forms its conjugate acid. Examples of identifying conjugate pairs in reactions are provided.

1. Chapter 14 Lecture
Basic Chemistry
Fourth Edition
Chapter 14 Acids and Bases
14.2 Brønsted−Lowry Acids and Bases
Learning Goal Identify
conjugate acid−base pairs
for Brønsted−Lowry acids
and bases.
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2. © 2014 Pearson Education, Inc.
Brønsted−Lowry Acids and Bases
According to the Brønsted–Lowry theory,
• an acid donates a proton (H+)
• a base accepts a proton (H+)
Free H+ ions do not exist in water. The H+ ion is
so strong that it bonds to a water molecule and
forms a hydronium ion, H3O+

3. Brønsted−Lowry Acids
A solution of hydrochloric acid forms when H+
transfers from hydrogen chloride to water.
Water is acting as a base in this reaction.
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4. Brønsted−Lowry Bases
Ammonia (NH3) reacts with water in which
• NH3 acts as the base, accepting H+ from water
• H2O acts as an acid in this reaction, donating
H+ to NH3
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5. Conjugate Acid−Base Pairs
In an acid–base reaction, there are two conjugate
acid–base pairs:
•an acid that donates H+ to form its conjugate base
conjugate acid–base pair 1
HA + B A− + BH+
conjugate acid–base pair 2
•a base that accepts H+ to form its conjugate acid
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6. Conjugate Acid−Base Pairs
In the reaction of HF and H2O, we can identify
the conjugate acid–base pairs as HF/F− along
with H3O+/H2O.
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7. Conjugate Acid−Base Pairs
In the reaction of NH3 and H2O, we can identify
the conjugate acid–base pairs as NH3/NH4
+ along
with H2O/OH−.
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8. Learning Check
A. Write the conjugate base of the following:
1. HBr
2. H2S
3. H2CO3
B. Write the conjugate acid of the following:
1. NO2
−
2. NH3
3. OH−
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9. Solution
A. Write the conjugate base of the following:
1. HBr Br−
2. H2S HS−
3. H2CO3 HCO3
−
B. Write the conjugate acid of the following:
1. NO2
−HNO2
2. NH3 NH4
+
3. OH− H2O
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10. Guide to Writing Conjugate
Acid−Base Pairs
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11. Learning Check
Identify the conjugate acid−base pairs in the
following reaction:
HI(aq) + NH3(aq) I−(aq) + NH4
+(aq)
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12. Solution
Identify the conjugate acid−base pairs in the
following reaction:
HI(aq) + NH3(aq) I−(aq) + NH4
+(aq)
Step 1 Identify the reactant that loses H+
as the acid. In the reaction, HI loses H+ to
form the product I−. Thus HI is the
conjugate acid, and I− is its base.
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13. Solution
Identify the conjugate acid−base pairs in the
following reaction:
HI(aq) + NH3(aq) I−(aq) + NH4
+(aq)
Step 2 Identify the reactant that gains H+
as the base. In the reaction, NH3 gains H+
to form the product NH4
+. Thus NH3 is
the conjugate base, and NH4
+ is its acid.
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14. Solution
Identify the conjugate acid−base pairs in the
following reaction:
HI(aq) + NH3(aq) I−(aq) + NH4
+(aq)
Step 3 Write the conjugate acid−base
pairs for each.
HI/I−, NH3/NH4
+
© 2014 Pearson Education, Inc.