1. Aim: How did Bronsted describe acids and bases? Do Now: 1.Take out a calculator and reference tables. 2.How did Arrehnius define an acid and a base?

2. Alternative definition for acids Bronsted-Lowry theory – an acid is any substance that donates a hydrogen ion. A hydrogen ion is a hydrogen without an electron. It is represented by the symbol H +. Therefore, a hydrogen ion is basically a proton. So, a Bronsted-Lowry acid is essentially a proton donor. Bronsted-Lowry includes Arrehnius acids as well as substances that donate protons that are not in aqueous solutions.

3. Alternative definition for bases Bronsted-Lowry defines bases as any substance that accepts a proton. Bronsted-Lowry includes the OH - ion as a base since it will accept a H +.

4. Acid Base Pairs When an acid loses a proton, the remaining portion of the acid has an unshared pair of electrons that can act as a base. Example: HCl  H + + Cl - Why is HCl considered to be an acid? Why is the Cl - ion considered to be a base? What is the difference between HCl and Cl - ? A pair of chemical formulas that differ only by the presence of a hydrogen ion are known as a conjugate acid-base pair.

5. Conjugate Acid-Base Pairs Acids cannot donate a proton unless there is a proton acceptor (base) available to accept the proton. Consider the following reaction: HNO 3 + H 2 O  H 3 O + + NO 3 - There are two acid-base pairs in this formula:

6. Practice Problems Name the acid base pairs in the following reactions: CH 3 NH 2 + H 2 O  CH 3 NH 3 + OH - HCl + H 2 O  H 3 O + + Cl -

7. Activity/Homework