Chapter 2.2 - Acids and Bases

p. 42-43 in Prentice Hall Biology, Miller and Levine

Double, double toil and trouble; Fire burn, and cauldron bubble…

What just happened with the witches and their pink potion?

Indicators

Chemicals that respond to a change in H ion concentration

Change color depending on whether substance is an acid or a base

Examples: litmus paper phenolphthalein

Ions

What is an ion?

Answer: positively or negatively charged atom

What is an Acid?

A compound that forms H+ ions in a solution

Example: Hydrochloric acid produced by stomach to digest food (HCl), carbonic acid in carbonated pop (HCO3), sulfuric acid in car batteries (H2SO4)

Characteristics of Acids

Contains Hydrogen (H+)

Turns litmus paper red

Tastes sour

Dissolves metal

What is a Base?

A compound that forms hydroxide ions (OH-) in a solution

Example: Lye

Characteristics of Bases

Contains Hydroxide

Turns litmus paper blue

Tastes bitter

Feels slippery

How Do We Measure Acids and Bases?

The pH scale

What does pH stand for

Power of Hydrogen

Scale ranges from 0 to 14

pH Scale: Acids

Acids have a pH below 7

Strong acids range from 1 to 3

Strong acid example: HCl

pH Scale: Bases

Bases have a pH above 7

Strong bases range from 11 to 14

Strong base example: lye, bleach, drano, Sodium hydroxide (NaOH)

pH Scale

pH increases tenfold

Water, Acids and Bases

A water molecule can react to form ions

Water is Neutral

Why is pure water considered “neutral”?

Pure water pH = 7

Number of positive hydrogen ions equal to negative hydroxide ions produced