1. 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. 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+
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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. Ammonia (NH3) reacts with water in which
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. A. Write the conjugate base of the following: 1. HBr 2. H2S 3. H2CO3
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. A. Write the conjugate base of the following: 1. HBr Br− 2. H2S HS−
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. Identify the conjugate acid−base pairs in the following reaction:
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. Identify the conjugate acid−base pairs in the following reaction:
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. Identify the conjugate acid−base pairs in the following reaction:
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+
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