1. Acids
and
Bases

2. Observations NaOH(aq) HCl(aq) Taste Bitter Sour
*Usually, but not always
NaOH(aq)
HCl(aq)
Taste
Bitter
Sour
Feel (choose slippery or not slippery)
Slippery
Not slippery
pH (# from the key) 14 1
Litmus (blue or red)
Blue
Red
Phenolphthalein
*Pink
*Clear/Cloudy white
Bromothymol
*Blue
*Yellow
Magnesium NR
Bubbles
Baking soda NR
Bubbles

3. Historical views on acids
O (e.g. H2SO4) was originally thought to cause acidic properties. Later, H was implicated, but it was still not clear why CH4 was neutral.
Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H3O+ (hydronium) ions in solution.
Ionization + H O H O Cl Cl H + +
The more recent Bronsted-Lowry concept is that acids are H+ (proton) donors and bases are proton acceptors

4. Bronsted-Lowry theory
An acid is a substance from which a proton (H+ ion) can be removed
A base is a substance that can remove a proton (H+ ion) from an acid
An acid-base reaction involves the transfer of a proton

5. Types of Acids Acids may have more than one proton to donate.
Monoprotic acids contain 1 hydrogen ion i.e. HCl(aq)
Diprotic acids contain 2 hydrogen ions, i.e. H2SO4(aq)
Triprotic acids contain 3 hydrogen ions, i.e. H3PO4(aq)

6. Conjugate acid-base pair
Two molecules or ions that are related by the transfer of a proton (H+) are called a conjugate acid-base pair.
(conjugate means “linked”)

7. The Bronsted-Lowry concept
In this idea, the ionization of an acid by water is just one example of an acid-base reaction. + Cl H O
acid
base
conjugate acid
conjugate base
conjugate acid-base pairs
Acids and bases are identified based on whether they donate or accept H+.
“Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H+.

8. Example: HBr(aq) + H20(l) -> H30+(aq) + Br-(aq)
Conjugate base of an acid is the particle that remains when a proton is removed from the acid (in this example: Br-(aq)
Conjugate acid of a base is the particle that results when the base receives the proton from the acid (in this example: H30+(aq)

9. Practice problems
Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:
HC2H3O2(aq) + H2O(l) → C2H3O2–(aq) + H3O+(aq)
acid
base
conjugate base
conjugate acid
conjugate acid-base pairs
OH –(aq) + HCO3–(aq) → CO32–(aq) + H2O(l)
base
acid
conjugate base
conjugate acid
conjugate acid-base pairs

10. Arrhenius Acids
An acid is a substance that produces Hydrogen ions, H+(aq) in water.
The hydrogen ion (H+) bonds with a water molecule to make a hydronium ion, H30+ (aq) (H+ + H20 -> H3O+)

11. Strong acids
A strong acid is an acid, which ionizes extremely well. Essentially all of the acid molecules are ionized. (lots of H3O+)
Example: HCl, HBr, HNO3, H2SO4, HClO4
Example:
HCl (aq) + H2O(l) -> H30+(aq) + Cl-(aq)
H2SO4(aq) +2H2O(l) -> 2H3O+ + SO42-(aq)
(Ionization equations show how they react with water to make H3O+)

12. Weak acid
A weak acid is an acid which ionizes poorly. Only a small percentage of the acid molecules actually ionize. (a few H3O+)
Example: HC2H3O2
HC2H3O2(aq) + H2O(l) → H3O+(aq) + C2H302-

13. Arrhenius Bases
A base is a substance that produces hydroxide ions, OH-, in water
A strong base is a base that dissociates 100% in aqueous solution.
Example:
NaOH(s) → Na+(aq) + OH-(aq)
KOH(s) -> K+(aq) + OH-(aq)
(Ionization equations: show how they make ions)

14. Weak base A weak base is a base which ionizes
poorly. Only a small percentage of the base molecules actually ionize.(a few
OH-
Example:
NH3(aq) + H2O(l) -> NH4+(aq) + OH-(aq)

15. Comparing the Arrhenius Theory and the Bronsted-Lowry Theory
Acid
Any substance that dissociates to form H+ in aqueous solution
Base
Any substance that dissociates to form 0H- in aqueous solution
Bronsted-Lowry
Acid
Any substance that provides a proton to another substance
Base
Any substance that receives a proton from an acid

16. Avoid confusing terms! Concentrated/Dilute vs Strong/Weak
A strong acid such as HCl can be concentrated (12mol/L) or dilute (0.5mol/L)
Concentrated or dilute refers to the amount of solute dissolved in the solvent
Strong or weak- refers to the degree of dissociation of ions in solutions.