ion consisting of a central atom surrounding molecules or ions called ligands via coordinate covalent bonds

coordinate covalent bond

(also, dative bond) covalent bond in which both electrons originated from the same atom

(K_f) (also, stability constant) equilibrium constant for the formation of a complex ion from its components

any species that can accept a pair of electrons and form a coordinate covalent bond

Lewis acid-base adduct

compound or ion that contains a coordinate covalent bond between a Lewis acid and a Lewis base

Lewis acid-base chemistry

reactions involving the formation of coordinate covalent bonds

any species that can donate a pair of electrons and form a coordinate covalent bond

molecule or ion acting as a Lewis base in complex ion formation; bonds to the central atom of the complex

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Chemistry 2e · 15.2 Lewis Acids and Bases

Lewis Acids and Bases: practice problems

12 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 62
Under what circumstances, if any, does a sample of solid AgCl completely dissolve in pure water?
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Exercises 64
Calculate the cadmium ion concentration, [Cd²⁺], in a solution prepared by mixing 0.100 L of 0.0100 M Cd(NO₃)₂ with 0.150 L of 0.100 NH₃(aq).
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Exercises 66
Sometimes equilibria for complex ions are described in terms of dissociation constants, K $_{d}$ . For the complex ion $AlF_{6}^{3-}$ the dissociation reaction is:
$AlF_{6}^{3-} ⇌ Al^{3+} + 6 F^{-}$ and
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Exercises 68
Using the dissociation constant, K $_{d}$ = 3.3 $\times$ 10–19, calculate the equilibrium concentrations of Cd²⁺ and CN– in a 0.250-M solution of $Cd (CN)_{4}^{2-} .$
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Exercises 70
Using the dissociation constant, K $_{d}$ = 2.2 $\times$ 10–34, calculate the equilibrium concentrations of Co³⁺ and NH₃ in a 0.500-M solution of $Co (NH_{3})_{6}^{3+} .$
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Exercises 72
Calculate the mass of potassium cyanide ion that must be added to 100 mL of solution to dissolve 2.0 $\times$ 10–2 mol of silver cyanide, AgCN.
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Exercises 74
A roll of 35-mm black and white photographic film contains about 0.27 g of unexposed AgBr before developing. What mass of Na₂S₂O₃·5H₂O (sodium thiosulfate pentahydrate or hypo) in 1.0 L of fixer is required to dissolve the AgBr as $Ag (S_{2} O_{3})_{2}^{3-}$ (K $_{f}$ = 4.7 10¹³)?
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Exercises 76
Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:
(a) $CO_{2} + OH^{-} ⟶ HCO_{3}^{-}$
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Exercises 78
Using Lewis structures, write balanced equations for the following reactions:
(a) $HCl (g) + PH_{3} (g) ⟶$
(b) $H_{3} O^{+} + CH_{3}^{-} ⟶$
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Exercises 80
In a titration of cyanide ion, 28.72 mL of 0.0100 M AgNO₃ is added before precipitation begins. [The reaction of Ag⁺ with CN– goes to completion, producing the $Ag (CN)_{2}^{-}$ complex.] Precipitation of solid AgCN takes place when excess Ag⁺ is added to the solution, above the amount needed to complete the formation of $Ag (CN)_{2}^{-} .$ How many grams of NaCN were in the original sample?
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Exercises 82
In dilute aqueous solution HF acts as a weak acid. However, pure liquid HF (boiling point = 19.5 °C) is a strong acid. In liquid HF, HNO₃ acts like a base and accepts protons. The acidity of liquid HF can be increased by adding one of several inorganic fluorides that are Lewis acids and accept F– ion (for example, BF₃ or SbF₅). Write balanced chemical equations for the reaction of pure HNO₃ with pure HF and of pure HF with BF₃.
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Exercises 84
Boric acid, H₃BO₃, is not a Brønsted-Lowry acid but a Lewis acid. (Hint: See the equation in Exercise 15.76)
(a) Write an equation for its reaction with water.
(b) Predict the shape of the anion thus formed.
(c) What is the hybridization on the boron, and is it consistent with the shape you have predicted?
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Key terms · 9

complex ion: ion consisting of a central atom surrounding molecules or ions called ligands via coordinate covalent bonds
coordinate covalent bond: (also, dative bond) covalent bond in which both electrons originated from the same atom
dissociation constant: (K_d) equilibrium constant for the decomposition of a complex ion into its components
formation constant: (K_f) (also, stability constant) equilibrium constant for the formation of a complex ion from its components
Lewis acid: any species that can accept a pair of electrons and form a coordinate covalent bond
Lewis acid-base adduct: compound or ion that contains a coordinate covalent bond between a Lewis acid and a Lewis base
Lewis acid-base chemistry: reactions involving the formation of coordinate covalent bonds
Lewis base: any species that can donate a pair of electrons and form a coordinate covalent bond
ligand: molecule or ion acting as a Lewis base in complex ion formation; bonds to the central atom of the complex

Learn 15.2 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 15.2 in the textbook · This section on openstax.org

Lewis Acids and Bases: practice problems

12 problems from the book, with its answers. Check your working, or have any of them explained to you on the whiteboard.

Exercises 62

Under what circumstances, if any, does a sample of solid AgCl completely dissolve in pure water?

Exercises 64

Calculate the cadmium ion concentration, [Cd²⁺], in a solution prepared by mixing 0.100 L of 0.0100 M Cd(NO₃)₂ with 0.150 L of 0.100 NH₃(aq).

Exercises 66

Sometimes equilibria for complex ions are described in terms of dissociation constants, K $_{d}$ . For the complex ion $AlF_{6}^{3-}$ the dissociation reaction is:

$AlF_{6}^{3-} ⇌ Al^{3+} + 6 F^{-}$ and

Exercises 68

Using the dissociation constant, K $_{d}$ = 3.3 $\times$ 10–19, calculate the equilibrium concentrations of Cd²⁺ and CN– in a 0.250-M solution of $Cd (CN)_{4}^{2-} .$

Exercises 70

Using the dissociation constant, K $_{d}$ = 2.2 $\times$ 10–34, calculate the equilibrium concentrations of Co³⁺ and NH₃ in a 0.500-M solution of $Co (NH_{3})_{6}^{3+} .$

Exercises 72

Calculate the mass of potassium cyanide ion that must be added to 100 mL of solution to dissolve 2.0 $\times$ 10–2 mol of silver cyanide, AgCN.

Exercises 74

A roll of 35-mm black and white photographic film contains about 0.27 g of unexposed AgBr before developing. What mass of Na₂S₂O₃·5H₂O (sodium thiosulfate pentahydrate or hypo) in 1.0 L of fixer is required to dissolve the AgBr as $Ag (S_{2} O_{3})_{2}^{3-}$ (K $_{f}$ = 4.7 10¹³)?

Exercises 76

Write the Lewis structures of the reactants and product of each of the following equations, and identify the Lewis acid and the Lewis base in each:

(a) $CO_{2} + OH^{-} ⟶ HCO_{3}^{-}$

Exercises 78

Using Lewis structures, write balanced equations for the following reactions:

(a) $HCl (g) + PH_{3} (g) ⟶$

(b) $H_{3} O^{+} + CH_{3}^{-} ⟶$

Exercises 80

In a titration of cyanide ion, 28.72 mL of 0.0100 M AgNO₃ is added before precipitation begins. [The reaction of Ag⁺ with CN– goes to completion, producing the $Ag (CN)_{2}^{-}$ complex.] Precipitation of solid AgCN takes place when excess Ag⁺ is added to the solution, above the amount needed to complete the formation of $Ag (CN)_{2}^{-} .$ How many grams of NaCN were in the original sample?

Exercises 82

In dilute aqueous solution HF acts as a weak acid. However, pure liquid HF (boiling point = 19.5 °C) is a strong acid. In liquid HF, HNO₃ acts like a base and accepts protons. The acidity of liquid HF can be increased by adding one of several inorganic fluorides that are Lewis acids and accept F– ion (for example, BF₃ or SbF₅). Write balanced chemical equations for the reaction of pure HNO₃ with pure HF and of pure HF with BF₃.

Exercises 84

Boric acid, H₃BO₃, is not a Brønsted-Lowry acid but a Lewis acid. (Hint: See the equation in Exercise 15.76)

(a) Write an equation for its reaction with water.

(b) Predict the shape of the anion thus formed.

Key terms · 9

complex ion: ion consisting of a central atom surrounding molecules or ions called ligands via coordinate covalent bonds
coordinate covalent bond: (also, dative bond) covalent bond in which both electrons originated from the same atom
dissociation constant: (K_d) equilibrium constant for the decomposition of a complex ion into its components
formation constant: (K_f) (also, stability constant) equilibrium constant for the formation of a complex ion from its components
Lewis acid: any species that can accept a pair of electrons and form a coordinate covalent bond
Lewis acid-base adduct: compound or ion that contains a coordinate covalent bond between a Lewis acid and a Lewis base
Lewis acid-base chemistry: reactions involving the formation of coordinate covalent bonds
Lewis base: any species that can donate a pair of electrons and form a coordinate covalent bond
ligand: molecule or ion acting as a Lewis base in complex ion formation; bonds to the central atom of the complex

Learn 15.2 on the whiteboard

The tutor teaches the whole section, drawing it out step by step and answering your questions as you go.

Read 15.2 in the textbook · This section on openstax.org