1. UNIT 6 INTRODUCTION TO CHEMISTRY
Chapter 21 Acids, Bases, and Salts

2. 21A – ACIDS AND BASES

3. IONIZATION OF WATER Most acids and base are dissolved in water
When substances are dissolved in water they become hydrated
The substance is broken down into ions
Can even happen to pure water and produces the hydronium ion and the hydroxide ion
2H2O H3O+ + OH-
H3O+ + OH H2O
Constant but continuous change, reaches a dynamic equilibrium
This equilibrium brings us to the definition of an acid and a base

4. ARRHENIUS DEFINITIONS
Facet – Page 485
Arrhenius was the first to give simple and straightforward definitions for acids and bases – the Arrhenius Model
Acid
Any substance that produces hydrogen ions in a water solution
Bare protons pulled from molecular compounds by the action of water molecules
Highly unstable and instantaneously bond to water molecules to form hydronium ions
Base
Any substance that produces hydroxide ions in a water solution
This model helped advance science during its time; however, it did not explain every kind of acid-base reaction
His model assumed that they only existed in water solutions which is not true

5. BRONSTED-LOWRY DEFINITION
Two chemist Johannes Bronsted and Thomas Lowry came up with the Bronsted-Lowry Model
Acids are any compound that is a proton donor (H+)
Base are compounds that accept protons
Acids and bases do not have to be dissolved in aqueous (water) solutions
Some compounds can behave as either acids or bases depending on the other reactants

6. POLYPROTIC ACIDS
Acids can contribute different amounts of H+ ions depending on their chemical formula
Those that only have one H+ ion are called monoprotic acids
HCl
Those that have two or more H+ ions are called polyprotic acids
It is more difficult to remove H+ each time
Look at table 21-1 on page 488

7. CONJUGATE ACIDS AND BASES
Conjugate base
The ion that remains after a molecular compound has donated a hydrogen ion
Every acid compound therefore becomes its own conjugate base after donating a proton
Conjugate acid
The molecule that accepts the H+ ion
H2O + H2O OH- + H3O+

8. PROPERTIES OF ACIDS & BASES
Sourness of foods, due to the presence of hyronium ions
You should never taste a chemical in the lab to see if it is an acid!
Conducts electricity
Corrodes metals
Reacts with carbonates and bicarbonates to form carbon dioxide gas

9. PROPERTIES OF ACIDS & BASES
Bitter taste
Slippery feel because they react with the oils on your skin
Do not taste or put a chemical on your skin to see if it is a base!
Emulsify, break down, organic materials
Oven cleaners
Unclogging sink drains
Severe burns
Acids and bases cancel each other out
Neutralization reactions

10. 21B - SALTS

11. SALTS
Ionic compounds produced from an acid-base reaction, or neutralization reaction
Double-displacement reaction that produce a salt and water
Example on next slide

12. VARIETY OF SALTS

13. 21C – ACIDITY AND ALKALINITY

14. ACID STRENGTH
Determined by the percentage of its first available hydrogen atoms that ionize

15. BASE STRENGTH
Measured by the number of proton acceptors it produces in an aqueous solution.

16. STRENGTHS

17. THE pH SCALE pH scale 1-14 Less than 7 = acidic
Greater than 7 = basic or alkaline
Equal to 7 = neutral
The lower the pH the more acidic
The higher the pH the more basic

18. MEASURING SOLUTION pH pH indicators
Change color in the presence of an acid or base
Litmus
One of the oldest know indicator compounds
Red will change to blue if basic
Blue will change to red if acidic
Phenolphthalein
Colorless in neutral or acidic
Deep pink in basic
Universal indicators
Manufactured papers or solutions that can read the pH to the nearest tenth

19. pH METERS A more objective technique to measure pH values
Measures voltage with a pH probe