Bronsted Lowry

Acid Base

Bronsted and Lowry

An ACID donates a proton (loses an H+)

A BASE accepts a proton (gains an H+)

Conjugate Acid Base Pairs

When an acid loses its hydrogen, it becomes a base (as it is able to gain a hydrogen again)

This is known as a conjugate base

At the same time, when a base gains a hydrogen in a reaction, it becomes a conjugate acid

Weak acids are found on pages 8 and 9 in your data booklet. The conjugate base formula for each acid is directly right to the acid formula. Each conjugate is the result of a loss of 1 hydrogen.

It is important to note that acids and bases may be noted as salts (ionic compounds)

When this occurs, you must dissociate the ions and allow the demonstration of the proton transfer (omit the spectator ions)

Example

Potassium hydrogen sulfate and sodium acetate are mixed in aqueous solution

Strong acids form Weak Bases

A strong acid will have a conjugate base that is weak

Strong acids lose its proton easily (and therefore will not accept a hydrogen easily)

A weaker acid will have a stronger conjugate base

Weak acids hold their protons more (and therefore will easily accept a hydrogen)

Kw = KaKb

Kw is the equilibrium constant for water (1.0 x 10-14)

Ka is the equilibrium constant for acids and can be found on page 8 and 9 in the data booklet

Kb is the equilibrium constant for bases and will have to be calculated using Kw = KaKb

Acid Reactions

HA + H2O H3O+ + A-

Base Reactions

Amphiprotic Substances

An amphiprotic substance is a chemical species that can donate or accept a proton

Substance must contain a hydrogen to donate

Substance must be able to accept a hydrogen (usually have a negative charge)

Reactions Favor if the weak acid has a higher Ka

than the conjugate acid in the same equation, the reaction will proceed in the forward direction and favor the products

if the weak acid has a lower Ka than the conjugate acid, the reaction will proceed in the reverse direction and favor the reactants

Example

Write the Bronsted-Lowry equation for the reaction between acetic acid and sodium sulfate. Label the conjugate acid base pairs and comment on whether the products or reactants are favored:

Example 2

Write the Bronsted-Lowry equation for the reaction between lactic acid and potassium hydrogen carbonate. Label the conjugate acid base pairs and comment on whether the products or reactants are favored:

C2H5OCOOH(aq) + HCO31-(aq) C2H5OCOO1-(aq) +

H2CO3(aq)

acid base conj. Base conj. Acid

K = [H2CO3(aq)][C2H5OCOO1-(aq)]

[C2H5OCOOH(aq)][HCO31-(aq)]

Favors products!

Kacid = 1.4x104 Kconjacid = 4.5x10-7