Brønsted-Lowry Model

Acids - proton (H+) donorsBases – accepts proton (H+)

Brønsted-Lowry Model• A Brønsted-Lowry acid is a proton donor• A Brønsted-Lowry base is a proton acceptor

Proton = Hydrogen ion = H+

The Brønsted definition means NH3 is a BASE in water — and water is itself an ACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H2OBaseAcidAcidBase

NH4+ + OH-NH3 + H2O

H+

H+

H+

Can you see how the HCl gives up a proton (H+) to the H2O?

Acid donates the proton (H+), base accepts it.Which is the acid and which is the base in the forward reaction?

CH3CO2H  +  H2O    H⇌ 3O+  +  CH3CO2-

CH3CO2H (acetic acid) – proton donor

H2O (water = base) – proton acceptor

Brønsted-Lowry Model• Amphoteric – something that can act as an

acid or a base.

• Water is acting as both an acid and a base

Base Acid Acid Base

Conjugate Pairs

Base Pairs to AcidAcid Pairs to Base

Conjugate Pairs• NH3, NH4+

• H2O, OH-

What are the conjugate acid base pairs?HCl + H2O H⇌ 3O+ + Cl-

HCl (acid), Cl- (base)H2O (base), H3O+ (acid)

Conjugate Pairs

Learning Check!

Label the acid, base, conjugate acid, and conjugate base in each reaction:

HCl + OH-   Cl- + H2O HCl + OH-   Cl- + H2O

H2O + H2SO4   HSO4- + H3O

+ H2O + H2SO4   HSO4- + H3O

+