Acid – Base Theory

Definitions: Arrhenius: An acid is a substance that increases the H + (or H 3 O + ) concentration in an aqueous solution. HCl + H 2 O  H 3 O + + Cl - A base is a substance that increases the OH - concentration in an aqueous solution. HCl  H + + Cl - NaOH(s)  Na + + OH - What about Na 2 CO 3 ????

Bronsted-Lowry: Acid = a proton donor in a RXN Base = a proton acceptor in a RXN HCl(aq) + NaOH(aq) → HOH + NaCl

Lewis: An acid is an electron pair acceptor H+H+ acid A base is an electron pair donor :O:H -.. H:O:H.. water

Acid/Base reactions: Produce water and a salt (and sometimes carbon dioxide). Hint: concentrate on the water first. Remember, water has the formula HOH. Complete and balance the following: HCl + KOH  HCl + Ca(OH) 2  HOH + KCl 2 Require equal numbers 2HOH + CaCl 2

1. Ba(OH) 2 + H 3 PO 4  2. HC 2 H 3 O 2 + NaOH  3. H 2 SO 4 + KOH  4. H 2 CO 3 + NaOH  5. Na 2 CO 3 + HCl 

6. NH 4 OH + H 2 SO 4  7. NH 3 + HCl  Give a definition of an acid: An acid is a proton donor (H + ) Give a definition of a base: A base is a proton acceptor

Conjugate acids and Conjugate bases HCl + KOH  HOH + KCl acidbase conj. acid conj. base Na 2 CO 3 + 2HCl  H 2 CO 3 + 2NaCl base acid conj. acid conj. base Na 2 CO 3 + 2HCl  H 2 O + CO 2 (g) + 2NaCl conj. base conj. acid acid base

NH 3 + HCl  NH Cl -

What is a strong Acid? An Acid that is 100% ionized in water. Strong Acids: 100% ionized (completely dissociated) in water. HCl + H 2 O  H 3 O + + Cl - often written as: HCl  H + + Cl -

Strong Acids: Perchloric HClO4 Chloric, HClO 3 Hydrobromic, HBr Hydrochloric, HCl Hydroiodic, HI Nitric, HNO 3 Sulfuric, H 2 SO 4 Strong Acids: 100% ionized (completely dissociated) in water. HCl + H 2 O  H 3 O + + Cl -

What is a strong Base? A base that is completely dissociated in water (highly soluble). NaOH(s)  Na + + OH - Strong Bases: Group 1A metal hydroxides (LiOH, NaOH, KOH, RbOH, CsOH) Heavy Group 2A metal hydroxides [Ca(OH) 2, Sr(OH) 2, and Ba(OH) 2 ]

Weak Acids: “The Rest”

Strong Acids: 100% ionized (completely dissociated) in water. HCl + H 2 O  H 3 O + + Cl - Note the “one way arrow”. Weak Acids: Only a small % (dissociated) in water. HC 2 H 3 O 2 + H 2 O  H 3 O + + C 2 H 3 O 2 - Note the “2-way” arrow. Why are they different?

Strong Acids: HCl ADD WATER to MOLECULAR ACID (H 2 O)

Strong Acids: (H 2 O) H3O+H3O+ H3O+H3O+ H3O+H3O+ H3O+H3O+ H3O+H3O+ Cl - Note: No HCl molecules remain in solution, all have been ionized in water.

HC 2 H 3 O 2  (H 2 O) Weak Acid Ionization: Add water to MOLECULES of WEAK Acid

HC 2 H 3 O 2  H C 2 H 3 O 2 - (H 2 O) Weak Acid Ionization: Note: At any given time only a small portion of the acid molecules are ionized and since reactions are running in BOTH directions the mixture composition stays the same. This gives rise to an Equilbrium expression, K a H C 2 H 3 O 2 - HC 2 H 3 O 2