15.2 Lewis Acids and Bases

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

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).

Sometimes equilibria for complex ions are described in terms of dissociation constants, K_d. For the complex ion $\text{AlF}_{6} ^{\text{3}−}$ the dissociation reaction is:

$\text{AlF}_{6} ^{\text{3}−} \rightleftharpoons \text{Al}^{\text{3}+} + 6 \text{F}^{−}$ and $K_{\text{d}} = \frac{\left[\text{Al}^{\text{3}+}\right] \left[\text{F}^{−}\right]^{6}}{\left[\text{AlF}_{6} ^{\text{3}−}\right]} = 2 \times 10^{- 24}$

Calculate the value of the formation constant, K_f, for $\text{AlF}_{\text{6}} ^{\text{3}−} .$

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 $\text{Co} \left(\text{NH}_{3}\right)_{6} ^{\text{3}+} .$

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.

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 $\text{Ag} \left(\text{S}_{2} \text{O}_{3}\right)_{2} ^{\text{3}−}$ (K_f = 4.7 $\times$ 10¹³)?

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 $\text{Ag} \left(\text{CN}\right)_{2} ^{−}$ complex.] Precipitation of solid AgCN takes place when excess Ag⁺ is added to the solution, above the amount needed to complete the formation of $\text{Ag} \left(\text{CN}\right)_{2} ^{−} .$ How many grams of NaCN were in the original sample?

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 p…

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

(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?