Acids and BasesLet’s start with a review of some things you may already know about Acids and Bases!

All about Acids•Acids are types of

organic molecules. We’ll look at their structures them later in the year.

•Characteristics of Acids• Tastes Sour • Conduct Electricity• Some acids react strongly with metals • Turns blue litmus paper red• Corrosive, which means they break down certain substances.

Examples of Acids•Acetic Acid = Vinegar

•Citric Acid = lemons, limes, & oranges. It is in many sour candies.

•Ascorbic acid = Vitamin C which your body needs to function.

•Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics, car batteries

Back to Basics!•Properties of Bases:•Bases have a bitter

taste.•Conduct Electricity•Turns Red litmus paper Blue

•Bases are usually slippery and gives soap, ammonia, other cleaning products some of their properties.

•Your blood is a basic solution.

Examples of Bases

•Magnesium Hydroxide = Milk of Magnesia – Help for upset stomach

•Drain Cleaner = Unclogs pipes

•Sodium Bicarbonate – Baking Soda = Useful for cooking and cleaning

Acid Definitions•Over time the definition of what is an acid or a base has changed with our understanding of molecules and how they interact.

•There are three definitions that we know:

•We will look at each of these in closer detail!

- Arrhenius (1880’s)- Bronsted-Lowry (1920’s)- Lewis (1923)

Arrhenius – Traditional Definition▫Acid: Substance that, when dissolved in water, increases the concentration of hydrogen ions (H+).

▫Base: Substance that, when dissolved in water, increases the concentration of hydroxide ions.

Problems with the Arrhenius Definition

•Arrhenius Model▫Is only applicable in solutions.▫Limited to molecules with Hydrogen and Hydroxide ions.

▫A more realistic representation of hydrochloric acid in water…..

Bronsted-Lowry Definition•Bronsted-Lowry•2 different individuals both proposed the same idea. Based on the idea that PROTONS (H+) are donated and accepted. ▫Acids – a substance that donates a proton.

▫Bases – a substance that accepts a proton.

Bronsted-Lowry Examples

Demo of the reaction:http://www.youtube.com/watch?v=U0M-Q65VQHs

+ +

HCl + NH3 Cl- + NH4+

What is the acid and what is the base?

- Acid is HCl because it donates the proton

- Base is NH3 because it accepts the proton

• An acid and base always work together to transfer a proton. One compound must donate and therefore, another must receive the proton.

•Which is the acid and which is the base in each of these reactions?

Bronsted-Lowry Examples

Water as an Acid and Base• So some molecules can act as an acid or

base like water in the above examples. •When a compound can act as an acid or a

base so it is said to be Amphoteric.

Conjugate Acid-Base Pairs•An acid and base always work in this type

of reaction. These reactions are also reversible.

•In many acid base reactions, the reactants and products change back and forth continuously. They do this in an effort to reach equilibrium!

•Identify the acid and base for the reaction:

Conjugate Acid-Base Pairs• If the reaction were flipped, then then the roles

would reverse!

Base Acid

AcidBase

Conjugate Acid-Base Pairs•A conjugate base is what remains after an acid has donated a proton.

•A conjugate acid is what is formed when a base accepts a proton.

Base

Acid Conjugat

e BaseConjugat

e Acid

Identify the Acid, Base, and their Conjugates:

Conjugate Acid/Base Practice:1) Identify the Acid, Base, and their

Conjugates:

NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

2)What is the Conj. Base of: 3)What is the Conj. Acid of:

A) HClO4 D) CN-

B) PH4+ E) SO4

2-

C) HCO3- F) HCO3

-

ClO4-

PH3

CO32-

HCN

HSO4-

H2CO3

Lewis Acids and Bases•G.N. Lewis noted that when a proton reacted with

a base, a pair of electrons were “donated” so the base could bond to the accepted proton. Hence, the base lost a pair of electrons.

Lewis Acid: Substances that accept a pair of electrons

Lewis Base: Substances that donate a pair of electrons

Strengths of Acids and Bases