CHAPTER 13 Acids and Bases 13.1 The Chemical Nature of Acids and Bases

What makes an acid an acid? What makes a base a base? Hydrochloric acid (HCl) is a strong acid in your stomach The acid in your stomach (HCl) can burn skin and dissolve metal! A base from the pancreas (HCO3–) helps to neutralize any acid that leaves the stomach What makes an acid an acid? What makes a base a base? Bicarbonate (HCO3–) ions are produced by the pancreas

Higher H+ concentration Lower H+ concentration From Chapter 4 Higher H+ concentration Lower H+ concentration The pH scale helps to determine whether a solution is acidic or basic.

Neutral solution H2O(l) H+(aq) + OH–(aq) Dissociation of water: This equilibrium lies heavily on the reactant side Only 1 out of 550 million water molecules is dissociated into a hydrogen (H+) ion In neutral water or solution, the concentrations of H+ and OH– are equal Neutral solution:

Acids Acidic solution: An acid dissolves in water to create more H+ ions than there are in neutral water Acidic solution:

Acids Acidic solution:

Bases NaOH(aq) → Na+(aq) + OH–(aq) Basic solution: Sodium hydroxide (NaOH) is also known as lye or caustic soda NaOH(aq) → Na+(aq) + OH–(aq) A base dissolves in water to create more OH– ions than there are in neutral water Basic solution:

Bases Basic solution:

Bases Potassium hydroxide (KOH) is used in alkaline batteries A base dissolves in water to create more OH– ions than there are in neutral water An alkaline substance is a salt of a group 1 or group 2 metal that dissolves in water to make a base.

Arrhenius theory More H+ ions More OH– ions

The hydronium ion The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.” Hydronium ion (hydrated proton) H+ is powerful because it has no electrons! When we talk about H+ in water, we’re really talking about H3O+

Ammonia is a proton acceptor so it is a base The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.” (aq) NH3 + H2O NH4+ + OH– Ammonia is a proton acceptor so it is a base

Nitric acid is a proton donor The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.” HNO3 → H+ + NO3– (aq) Nitric acid is a proton donor It is indeed an acid

Acids and bases always act in pairs called conjugate acid-base pairs! A proton that is donated by one chemical (an acid) must be accepted by another chemical (a base) Acids and bases always act in pairs called conjugate acid-base pairs!

Acid-base pairs

Acid-base pairs NH3 is the conjugate base of NH4+ NH4+ is the conjugate acid of NH3

Acid-base pairs HCl is the conjugate acid of H3O+ H3O+ is the conjugate base of HCl

Water can act as either an acid or a base! NH3 + H2O NH4+ + OH– H+ donor (acid) Water can act as either an acid or a base! HCl + H2O H3O+ + Cl– H+ acceptor (base) amphoteric: a substance that can act as either an acid or a base under different circumstances.

Identifying acids HCl(aq) → H+(aq) + Cl–(aq) hydrochloric acid The H+ that gets donated is written first H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq) ascorbic acid (vitamin C)

Identifying acids HCl(aq) → H+(aq) + Cl–(aq) 1 M A strong acid dissociates completely A weak acid dissociates only partially H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq) 1 M < 0.02 M

The OH group at the end reminds chemists that a chemical is a base Identifying bases The OH group at the end reminds chemists that a chemical is a base Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq) calcium hydroxide Not all bases have an OH group!

A strong base dissociates completely Identifying bases Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq) 1 M 2 M A strong base dissociates completely KOH(aq) → K+(aq) + OH–(aq) 1 M

Identifying bases NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) 1 M ~ 0.004 M A weak base yields much less than 1 OH– ion per molecule of base in solution. For example, 1 mole of ammonia (NH3) produces about 0.004 moles of OH– ions.

Arrhenius: Brøndsted-Lowry: pH range: [H+] and [OH–]: Acids Bases produce H+ ions in aqueous solutions produce OH– ions in aqueous solutions donate H+ ions accept H+ ions Arrhenius: Brøndsted-Lowry: pH < 7 pH > 7 [H+] > [OH–] [H+] < [OH–] pH range: [H+] and [OH–]: The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton” Water can act as either an acid or a base

HCl(aq) → H+(aq) + Cl–(aq) Strong: Complete dissociation HCl(aq) → H+(aq) + Cl–(aq) 1 M Acids 1 M < 0.02 M H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq) Weak: Partial dissociation

HCl(aq) → H+(aq) + Cl–(aq) Strong: Complete dissociation HCl(aq) → H+(aq) + Cl–(aq) 1 M Acids 1 M < 0.02 M H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq) Weak: Partial dissociation Strong: Complete dissociation Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq) 1 M 2 M Bases Weak: Partial dissociation 1 M ~ 0.004 M NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)