1. (a) Which is the stronger Bronsted acid, HCO₃⁻ or NH₄⁺? Which has the stronger conjugate base?
2. (b) Is a reaction between HCO₃^- ions and NH₃ product- or reactant-favored at equilibrium?

HCO₃⁻(aq) + NH₃(aq) ⇄ CO₃²⁻(aq) + NH₄⁺(aq)

(c) You mix solutions of sodium hydrogen phosphate and ammonia. The net ionic equation for a possible reaction is

HPO₄^2‒(aq) + NH₃(aq) ⇄ PO₄^3‒(aq) + NH₄⁺(aq)

Does the equilibrium lie to the left or to the right for this reaction?

Interpretation:

The stronger bronsted acid between HCO3− and NH4+ and the stronger conjugate base has to be stated.

Concept Introduction:

Bronsted –Lowry definitions:

A Bronsted –Lowry acid is a proton donor, it donates a hydrogen ion, H+

A Bronsted-Lowry base is a proton acceptor, it accepts a hydrogen ion H+.

Bronsted –Lowry conjugate acid-Base pairs:

When an acid is dissolved in water, the acid (HA) donates a proton to water to form a new acid (conjugate acid) and a new base (conjugate base).

An equilibrium constant (K) is the ratio of the concentration of products and reactants raised to appropriate stoichiometric coefficient at equilibrium.

The reaction of any acid HA with water is written as,

  HA(aq)+H2O(l)⇌H3O+(aq)+A−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Ka=[H3O+][A−][HA]

An equilibrium constant (K) with subscript a indicates that it is an equilibrium constant of an acid in water.

The reaction of any base B with water is written as,

  B(aq)+H2O(l)⇌BH(aq)+OH−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Kb=[BH][OH−][B]

An equilibrium constant (K) with subscript b indicates that it is an equilibrium constant of the base in water.

The dissociation constant (Ka) for HCO3− is 4.8×10−11.

The dissociation constant (Ka) for NH4+ is 5.6×10−10.

The reaction of HCO3− with water is written as,

  HCO3−(aq)+H2O(l)⇌H3O+(aq)+CO3−2(aq)

The dissociation constant for HCO3− ion is expressed as,

Ka=[H3O+][CO3−2][HCO3−]

A smaller value of Ka=4.8×10−11 indicates that the ionization product is weakly favored because the product [H3O+][CO3−2] is less than the equilibrium concentration of the weak acid [HCO3−]

Interpretation:

The reaction between HCO3− and NH3 at equilibrium is a product favored or a reactant favored has to be stated.

Concept Introduction:

An equilibrium constant (K) is the ratio of the concentration of products and reactants raised to appropriate stoichiometric coefficient at equilibrium.

The reaction of any acid HA with water is written as,

  HA(aq)+H2O(l)⇌H3O+(aq)+A−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Ka=[H3O+][A−][HA]

An equilibrium constant (K) with subscript a indicates that it is an equilibrium constant of an acid in water.

The reaction of any base B with water is written as,

  B(aq)+H2O(l)⇌BH(aq)+OH−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Kb=[BH][OH−][B]

An equilibrium constant (K) with subscript b indicates that it is an equilibrium constant of the base in water.

Interpretation:

The reaction between HPO4−2 and NH3 at equilibrium is a product favored or a reactant favored reaction has to be stated.

Concept Introduction:

An equilibrium constant (K) is the ratio of the concentration of products and reactants raised to appropriate stoichiometric coefficient at equilibrium.

The reaction of any acid HA with water is written as,

  HA(aq)+H2O(l)⇌H3O+(aq)+A−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Ka=[H3O+][A−][HA]

An equilibrium constant (K) with subscript a indicates that it is an equilibrium constant of an acid in water.

The reaction of any base B with water is written as,

  B(aq)+H2O(l)⇌BH(aq)+OH−(aq)

The relative strength of an acid and base in water can be also expressed quantitatively with an equilibrium constant as follows:

Kb=[BH][OH−][B]

An equilibrium constant (K) with subscript b indicates that it is an equilibrium constant of the base in water.