This lesson explores how acid–base reactions can shift the dissolution equilibria of sparingly soluble salts. This connection helps explain environmental effects such as ocean acidification and practical effects such as tooth decay.
A coupled equilibrium occurs when two or more reactions share a species. When a salt dissolves, its ions may participate in another reaction. If that second reaction removes one of the dissolved ions, the dissolution equilibrium can shift to produce more ions and dissolve more solid.
All flashcards
What is a coupled equilibrium?
It is a system of two or more equilibria that share at least one chemical species, so a change in one reaction can affect the others.
Why does acid increase calcium carbonate solubility?
Hydronium protonates carbonate to form bicarbonate. Removing carbonate from the dissolution equilibrium encourages more calcium carbonate to dissolve.
How is ocean acidification connected to coral reefs?
Dissolved carbon dioxide contributes to ocean acidity. Acid converts carbonate into bicarbonate, making calcium carbonate reef skeletons more prone to dissolution.
How can bacterial acids contribute to cavities?
Hydronium from bacterial acids reacts with hydroxide released as hydroxyapatite dissolves. Removing hydroxide shifts the dissolution equilibrium toward further enamel loss.
Why can fluoride protect enamel?
Fluoride can replace hydroxide in hydroxyapatite to form fluorapatite. Because fluoride is a weaker base, it reacts less extensively with acid, making the mineral more resistant to acid dissolution.
Quiz questions
How can complex-ion formation increase the amount of a sparingly soluble metal salt that dissolves?Answer: The ligand binds dissolved metal ions, lowering their free-ion concentration.
For a net reaction formed by adding a dissolution equilibrium to a complex-formation equilibrium, how are the equilibrium constants combined?Answer: The constants are multiplied.
For aluminum hydroxide dissolving in pure water, if its molar solubility is s, which relation describes its solubility product?Answer: Ksp=27s4
A buffer has equal concentrations of acetic acid and acetate. If the acetic acid pKa is 4.74, what is the buffer pH?Answer: 4.74
When calculating total thiosulfate needed to dissolve silver bromide by complex formation, what must be included?Answer: Thiosulfate bound in complexes and free thiosulfate at equilibrium.
Based on Chemistry 2e by Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson, PhD (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.