Acids and Bases Introduction

Chem 12

Chapter 14 Pg 544-559

Properties of Acids

• Turn blue litmus paper red• Neutralize the properties of bases• React with certain metals to produce hydrogen

gas• React with carbonate compounds to produce

carbon dioxide gas• Have a sour taste• Are electrolytes• Have a pH less than 7

Properties of Bases

• Turn red litmus paper blue• Turn the indicator phenolphthalein from

colorless to red• Neutralize the properties of acids• Have a bitter taste• Are electrolytes• Are slippery to the touch• Have a pH greater than 7

Common Acids

Sulfuric Acid H2SO4

Nitric Acid HNO3

Phosphoric Acid H3PO4

Hydrochloric Acid HCl

Acetic Acid CH3COOH

Carbonic Acid H2CO3

Battery acid

Used to make fertilizersand explosives

Food flavoring

Stomach acid

Vinegar

Carbonated water

Common Bases

Sodium hydroxide NaOH lye or caustic soda

Potassium hydroxide KOH lye or caustic potash

Magnesium hydroxide Mg(OH)2 milk of magnesia

Calcium hydroxide Ca(OH) 2 slaked lime

Ammonia water NH3 H2O household ammonia

Name Formula Common Name

.

Definition of Acid• An operational definition is a definition based on

observed experimental properties.• An operational definition of an acid is that it is a

substance that turns blue litmus paper red and has a pH less than 7.

• An operational definition of a base is that it is a substance that turns red litmus paper blue and has a pH greater than 7.

• A conceptual definition attempts to explain why a substance behaves the way it does.

• Arrhenius theory (only applies to solutions made with water) and Bronsted-Lowery acid base definitions are conceptual

Arrhenius Acid-Base Theory

• An acid is a substance that produces hydrogen ions, H+ (aq), in water. Hydrogen ions always combine with at least one water molecule to produce hydronium ions, H3O+

HCl(g) + H2O(l) < -- > H3O+ (aq) + Cl-(aq)

Arrhenius acid (hydrochloric acid)

Arrhenius Base

• A base is a substance that produces hydroxide ions, OH- (aq), in water.

NaOH(s) + H2O(l) → Na+ (aq) + OH-(aq)

Arrhenius base (sodium hydroxide)

• According to the Arrhenius acid-base theory, the hydronium ion explains the chemical properties of an acid, and the hydroxide ion explains the chemical properties of a base.

• acid-base neutralization the hydronium ion from the acid reacts with the hydroxide ion from the base to produce water.

H3O+(aq) + OH-(aq) → 2H2O(l)

Brønsted-Lowry acid-base theory

• An acid is proton (H+ ion) donor, and a base is a proton (H+ ion) acceptor.

• This is a better definition because it is not limited to solutions where water is the solvent.

Acid (proton donor)

Base (proton acceptor)

Monoprotic Acids

• Bronsted-Lowry acids can be monoprotic-capable of losing one proton, such as:

HCl(aq) + H2O(l) H3O+(aq) + Cl-(aq)

HNO3(aq) + H2O(l) H3O+(aq) + NO3

-(aq)

• Bronsted-Lowry acids can also be polyprotic-capable of losing (donating) more than one proton.

• Polyprotic acids lose their protons in separate steps or reactions.

Diprotic Acids

• Diprotic acids are capable of losing two protons.

H2SO4(aq) + H2O(l) HSO4-(aq) + H3O+

(aq)

HSO4-(aq) + H2O(l) SO4

2-(aq) + H3O+

(aq)

Polybasic Bases

• Bronsted-Lowry bases can be monobasic-capable of supplying one hydroxide ion such as

NaOH(s) + H2O(l) Na+(aq) + OH-

(aq)

• Polybasic bases can be capable of supplying more than one hydroxide ion.

• Dibasic are capable of supplying two hydroxide ions.

Mg(OH)2(s) + H2O(l) Mg2+(aq) + 2OH-

(aq)

Conjugate Acid-Base Pairs

• A pair of substances that only differ by one proton.

• Conjugate = “linked together”H+ donor

NH4+ + CO3

-2 < -- > NH3 + HCO3-

Acid base conjugate conjugate

base acid

Conjugate acid and base, HA/A-, differ by one proton.

The conjugate acid of a base is the base plus the attached proton and the conjugate base of an acid

is the acid minus the proton.

Conjugate Acid-Base Pairs

Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 280

Amphoteric

• Substances that can act like an acid in one reaction, and like a base in another type of reaction.

• Example: baking soda’s anion HCO3-

1. HCO3- + OH- < -- > CO3-2 + H2O (donates

a H+, so acts like an acid)

2. HCO3- + H3O+ < -- > H2CO3 + H2O (accepts a H+, so acts like a base)

Practice:

Finish these questions for homework

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