1 The Chemistry of Acids and Bases Chapter 16

2 Some Properties of Acids þ Produce H + ions in water þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”

3 Some Properties of Bases  Produce OH - ions in water  Taste bitter, chalky  Are electrolytes  Feel soapy, slippery  React with acids to form salts and water  pH greater than 7  Turns red litmus paper to blue “Basic Blue”

4 Strong Acids and Strong Bases ACIDS HCl HBr HI HNO 3 H 2 SO 4 HClO 3 HClO 4 BASES LiOH NaOH KOH RbOH CsOH Sr(OH) 2 Ba(OH) 2

5 Arrhenius acid is a substance that produces H + in water Arrhenius base is a substance that produces OH - in water HCl  H + + Cl - NaOH  Na + + OH - Acid/Base theories #1: The Arrhenius theory – describes acids and bases by the type of ion each produces in water

6 Acid/Base theories #2: Brønsted – Lowry – describes acids and bases in terms of protons Acids – proton donor Bases – proton acceptor A “proton” is really just a hydrogen atom that has lost its electron!

7 The Brønsted – Lowry Theory When an acid dissolves in water the hydrogen ion leaves the acid and bonds to the water molecule, forming hydronium ion (H 3 O+) HCl + H 2 O  H 3 O + + Cl- When a base dissolves in water, a hydrogen leaves from water and bonds to the base, leaving hydroxide ion (OH-) NH 3 + H 2 O ↔ NH OH -

8 Conjugate Acids and Bases ( part of the Brønsted – Lowry Theory) Conjugate Acid- is the species produced when a base accepts a hydrogen ion from an acid. Conjugate Base- is a species that results when an acid donates a hydrogen ion to form a base. Conjugate Acid-Base Pair- consists of two substances related to each other by the donating and accepting of a single hydrogen ion. Amphoteric- water and other substances that can act as both an acid and a base

9 Conjugate Pairs HC 2 H 3 O 2 + H 2 O  C 2 H 3 O H 3 O + Acid Base Conj. Base Conj. Acid How to identify conjugate acid – base pairs: An acid’s formula begins with an ionizable hydrogen (HA) Its conjugate base is the particle formed after the hydrogen ion leaves (A-) A base accepts the hydrogen ion from the acid Its conjugate acid is the particle formed after the hydrogen ion is added

10 Try to identify acid, base, conjugate acid and conjugate base NH 4 + (aq) + OH - (aq)  NH 3 (aq) + H 2 O (l) CH 3 NH 2 + H 2 O  CH 3 NH OH -

11 pH The pH of a solution is a measure of the hydronium ion concentration in that solution The formula for calculating pH is: pH = -log [H 3 O + ] *** For ALL strong acids, the hydronium ion concentration is equal to the concentration of the acid given in the problem To calculate the pH of a strong base, use this formula: pH = – (-log[OH - ]) *** For ALL strong bases, the hydroxide ion concentration is equal to the concentration of the base given in the problem

12 pH of salts Consult the following chart to determine whether a salt is acidic, basic or neutral For example KBr is neutral, because KOH and HBr are both strong, but NaF is basic because NaOH is strong and HF is weak If the cation is from a… And the anion is from a… The salt is… Strong baseStrong acidNeutral (pH = 7.0) Strong baseWeak acidBasic (pH > 7.0) Weak baseStrong acidAcidic (pH < 7.0)