Introduction to Acids and Bases

What are Acids and Bases? There are two models: Arrhenius (He came first and most often this is what is used as a definition for an acid or a base) Bronsted-Lowry (they expanded they definitions to include substances that didn’t necessarrily meet the requirements of Arrehenius’ definition)

Acid: Increases H+ concentration in water. Arrhenius Acid: Increases H+ concentration in water. The individual ions will separate! Examples: HCl H+ + Cl- HNO3 H+ + NO3- H2SO4 2H+ + SO4 2- H2O

Base: Increases OH- concentration in water. Arrhenius Base: Increases OH- concentration in water. The individual ions will separate! Examples: NaOH Na+ + OH- LiOH Li+ + OH- Ca(OH)2 Ca2+ + 2OH- H2O Note: Contain OH- as anion in formula!

In a formula: Acids will start with an H Bases will end in an OH

Bronsted-Lowry Acid: A substance that can DONATE a proton (H+) to another substance. Base: A substance that ACCEPTS a proton (H+) from another substance. Examples: NH3 + HCl  NH4 + Cl- CO3-2 + HBr  HCO3 -1 + Br-

Bronsted-Lowry Acids further grouped by # of H+ they can donate: Monoprotic: HF, HCl, HNO3 , HClO3 Diprotic: H2SO3 , H2SO4 , H2CO3 Triprotic: H3PO4

Comparison Arrhenius Acid HCl HBr H2SO4 H3PO4 etc. Bronsted-Lowry Acid Same as above

Comparison Arrhenius Base NaOH LiOH Ca(OH)2 Bronsted-Lowry Base NH3 , OH - , HCO3 -

These are called conjugate acids and bases. A better way to identify acids and bases is by LOOKING FOR PROTON ACCEPTORS AND DONATORS NH3 + H2S  NH4+ + SH- These are called conjugate acids and bases.

Conjugate Acids and Bases (Note: Conjugates are on the product side, the right side, of the chem. eqn.) Conjugate Acid: -the substance formed when a base gains a hydrogen ion. NH3 + H2S  NH4+ + SH- conj. acid

Conjugate Acids and Bases Conjugate Base: -the substance formed when an acid loses a hydrogen ion. NH3 + H2S  NH4+ + SH- conj. base

Conjugate Acids and Bases Conjugate Acid-Base Pair: consists of two substances related by the loss or gain of a single hydrogen ion NH3 + H2S  NH4+ + SH- Base Acid Conj. Conj. Acid Base

Conjugate Acids and Bases Try These: Label acid, base, conjugate acid and conjugate base. HBr + H2O H3O+ + Br- NOTE: H3O+ called “hydronium ion”

Conjugate Acids and Bases Try These: Label acid, base, conjugate acid and conjugate base. HCl + OH- HOH + Cl-

Conjugate Acids and Bases Try These: Label acid, base, conjugate acid and conjugate base. CO3 2- + H2O HCO3 - + OH -

Conjugate Acids and Bases Try These: Label acid, base, conjugate acid and conjugate base. CO3 2- + H2O HCO3 - + OH - NOTE: H2O can act as an acid or a base. Substances that can do this called ‘amphoteric’!

To Summarize… • Acids donate a proton, become conjugate bases. • Bases accept a proton, become conjugate acids.

Check Your Understanding Write the conjugate acid to the following bases: SO4 2- Cl - NO2 - HCO3 -

Check Your Understanding Write the conjugate acid to the following bases: SO4 2- HSO4 - Cl - HCl NO2 - HNO3 HCO3 - H2CO3

Check Your Understanding Write the conjugate base to the following acids: HNO3 H2SO3 NH3 HCO3 -

Check Your Understanding Write the conjugate base to the following acids: HNO3 NO3 - H2SO3 HSO3 - NH3 NH2 - HCO3 - CO3 2-

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