For each equilibrium, label the stronger acid, stronger...

For each equilibrium, label the stronger acid, stronger base, weaker acid, and weaker base. For which reaction(s) does the position of equilibrium lie toward the right? For which does it lie toward the left? (a) $\mathrm{H}_{3} \mathrm{PO}_{4}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{H}_{2} \mathrm{PO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O}$ (b) $\mathrm{H}_{2} \mathrm{O}+\mathrm{Cl}^{-} \rightleftharpoons \mathrm{HCl}+\mathrm{OH}^{-}$ (c) $\mathrm{HCO}_{3}^{-}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{CO}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O}$

For each equilibrium, label the stronger acid, stronger base, weaker acid, and weaker base. For which reaction(s) does the position of equilibrium lie toward the right? For which does it lie toward the left?
(a) $\mathrm{H}_{3} \mathrm{PO}_{4}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{H}_{2} \mathrm{PO}_{4}^{-}+\mathrm{H}_{2} \mathrm{O}$
(b) $\mathrm{H}_{2} \mathrm{O}+\mathrm{Cl}^{-} \rightleftharpoons \mathrm{HCl}+\mathrm{OH}^{-}$
(c) $\mathrm{HCO}_{3}^{-}+\mathrm{OH}^{-} \rightleftharpoons \mathrm{CO}_{3}^{2-}+\mathrm{H}_{2} \mathrm{O}$

Key Concepts

Equilibrium Position Determination

Determining the equilibrium position requires comparing the relative strengths of the acids and bases involved. If the reaction forms a weaker acid and a weaker base from a stronger acid and a stronger base, the equilibrium lies to the right (favoring products). Conversely, if the products are a stronger acid or base compared to the reactants, the equilibrium will lie to the left. This principle helps predict which side of the reaction is favored under equilibrium conditions.

Acid and Base Strength

The strength of an acid or base refers to its tendency to donate or accept a proton, respectively. In any equilibrium, the reaction tends to favor the formation of the weaker acid and base. Comparing the strengths of the acids and bases on both sides of an equilibrium is essential to predict the reaction direction, as stronger acids and bases will react to form their weaker conjugate counterparts in order to reach equilibrium.

Conjugate Acid–Base Pairs

A conjugate acid–base pair consists of two species that differ by one proton. When an acid donates a proton, it forms its conjugate base, and when a base accepts a proton, it forms its conjugate acid. This relationship is fundamental in equilibrium analysis, as the relative strengths of a conjugate acid–base pair determine the direction in which the equilibrium will lie. A stronger acid generally has a weaker conjugate base, and vice versa.

Acid–Base Equilibrium

This concept involves the dynamics between acids and bases in solution, where an acid donates a proton (H+) to a base. In a reaction, one identifies the acid–base pair by locating the species that lose or gain protons. Understanding acid–base equilibrium is crucial as it determines how far a reaction will proceed and which side of the equilibrium is favored, based on the strength of the acid and its conjugate base relative to those on the opposite side.

Transcript

00:02 The equilibrium between phosphoric acid and hydroxide, forming dihydrogen, phosphate, and water.

00:31 The protonated species will be the acids, and the unprotonated species will be the bases.

00:39 So we have an acid and a base on both sides of the equation.

00:47 Acids are phosphoric acid and water.

00:54 The bases are hydroxide and dihydrogen phosphate.

01:11 Now between the two acids, phosphoric acid is more acidic than water.

01:20 We know water has a ph of around 7.

01:23 It's distilled.

01:26 Then between the bases, hydroxide is a strong base.

01:29 Dihydrogen phosphate is not.

01:32 And it's the case that the stronger acid and stronger base will be on the same side of the equation.

01:41 So in this case, the stronger acid and stronger base are on the left.

01:46 The weaker acid and weaker base are on the right.

01:51 And the equilibrium will favor the side with the weaker acid and weaker base.

01:57 So that means the equilibrium for this example will lie to the right.

02:03 When we consider water and chloride in equilibrium with hydrochloric acid and hydroxide, acids are the protonated species against water and hydrochloric acid.

02:31 Bases are the anions, so chloride and hydroxide.

02:47 Now comparing the acids, hydrochloric acid is a stronger acid than water.

02:53 And hydroxide is a stronger base than chloride...

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