Exercise 1. Which acid in each pair has the strongest conjugate base?
HF is a weaker acid than HBr. HF has the stronger conjugate base, F–.
b) HCN or HSO4–
HCN is a weaker acid than HSO4. HCN has the stronger conjugate base, CN–.
c) H2PO4– or HPO42-
HPO42- is a weaker acid than H2PO4–. It is much more difficult for a hydrogen to be removed from a species with a -2 charge. The conjugate base of the weaker acid is the stronger base and is PO43-.
d) NH4+ or CH3NH3+
CH3NH3+ is a weaker acid than NH4+. The conjugate base of the weaker acid is the stronger base and is CH3NH3.
e) H3O+ or H2O
H2O is a weaker acid than H3O+. The conjugate base of the weaker acid is the stronger base and is OH–.
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Exercise 2. Which base in each pair has the strongest conjugate acid?
The Cl– ion would have the stronger conjugate acid, HCl.
b) NH3 or HSO4–
The HSO4– ion would have the stronger conjugate acid, H2SO4.
c) O2- or CN–
The CN– ion would have the stronger conjugate acid, HCN.
d) H2S or H2O
The H2O would have the stronger conjugate acid, H3O+.
The ClO3– would have the stronger conjugate acid, HClO.
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Exercise 3. Are products or reactants favored in the following reaction?
The reactants are favored because H2S and H2O are the weaker acid and base.
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Exercise 4. Are products or reactants favored in the following reaction?
The reactants are favored because HClO and H2O are the weaker acid and base.
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Exercise 5. Are products or reactants favored in the following reaction?
The products are favored because NH4+ and ClO– are the weaker acid and base.
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Exercise 6. Order the following acids in each set from weakest to strongest acid strength. Explain.
The acids from weakest to strongest are:
H2O < H2S < H2Se
Going down a group, we look at bond strength. The bond strength decreases, meaning acid strength increases, as we go down the group.
b) NH3, PH3 AsH3
The acids from weakest to strongest are:
NH3 < PH3 < AsH3
Going down a group, we look at bond strength. The bond strength decreases, meaning acid strength increases, as we go down the group.
c) HBrO2, HBrO, HBrO3
The acids from weakest to strongest are:
HBrO < HBrO2 < HBrO3
The acid strength increases with increasing number of oxygens.
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Exercise 7. Order the following acids in each set from weakest to strongest acid strength. Explain.
Acid strength from weakest to strongest is:
H3PO4 < H2SO3 < HClO4
Perchloric acid is a strong acid. Both phosphoric and sulfurous acids are weak acids. Sulfurous acid is stronger than phosphoric acid because the sulfur atom has a higher electronegativity than the phosphorous atom.
b) H2SO3, H2SO4, HSO2–
Acid strength from weakest to strongest is:
HSO2– < H2SO3 < H2SO4
Sulfuric acid is a strong acid. Both sulfurous and hydrogen sulfate are weak acids. Sulfurous acid is stronger than hydrogen sulfate because hydrogen sulfate is negatively charged, and it would be more difficult for a hydrogen atom to be transferred.
c) HCO3–, HNO3, H2CO3
Acid strength from weakest to strongest is:
HCO3– < H2CO3 < HNO3
HNO3 is a strong acid while both HCO3– and H2CO3 are weak acids. The HCO3– is a weaker acid than H2CO3 because it is more difficult to transfer a hydrogen from a negatively charged species.
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Exercise 8. Order the following organic acids from weakest to strongest acid.
From weakest to strongest acid:
The chlorine atom is electronegative and will pull electrons toward itself increasing the partial positive charge on the carbon atom. The carbon atom then pulls the electrons closer from the acidic hydrogen making the bond weaker, therefore, a stronger acid.