Acids, Bases, and pHChapter 9Section 1

D12 - Explain the chemical composition of acids and bases, and explain the change of pH in neutralization reactions.

D12

What do you know about acids? Can you name some acids? Have you ever had lemonade? The juice of

a lemon is an acid. So, this means that not all acids are alike, since you can safely drink lemonade, but not some other acids.

Acids

Acids are compounds, which means that they are made of more than one type of element.

One of the elements is always HYDROGEN.

Properties:◦Taste sour◦They will turn blue litmus paper red◦They will conduct electric current◦They are corrosive◦They can sting in an open cut (weaker acids),

or can damage your skin (stronger acids)

So, what are acids?

When dissolved in water, they ionize.

This means that they split apart into the ions that make up the acid. H+ is ALWAYS formed.

HCl H+ + Cl-

One of the ions formed is the Hydrogen or H+ ion

This can attach to the water molecules to form hydronium ions, H3O+

H20 + H+ H3O+

How do acids work?

Strong acids ionize completely

Each molecule splits into its ionsThis makes a high concentration of hydrogen and hydronium ions in the liquid.

Weak acids do not ionize completely.This makes a lower concentration of hydronium ions in the liquid.

Strong vs. Weak Acids

Which of the following "molecular" pictures best represents a concentrated solution of

the weak acid HA?

You try …

A B

Since there is complete ionization in water, this is a strong acid

An electrolyte is a liquid which can conduct electricity

Nitric Acid conducts electricity well, which means it is a strong electrolyte

HNO3 + H2O H3O+ NO3-

Nitric Acid

This is an example of a weak acid

Weak acids do not conduct electricity well

This means that they are weak electrolytes

CH3COOH + H2O H3O + CH3COO-

Acetic Acid

Acids are corrosive They can damage living tissues Acidic vapors can be harmful to eyes,

mouth and lungs Wear safety goggles, gloves, lab apron Overall, be careful!

Acid Safety

Bases!

What’s next?

What do you know about bases? Can you name some bases? Do you use soaps or detergents? These are

bases. Like acids, not all bases are alike.

Bases

A base is a compound that increases the number of hydroxide ions (OH-) when mixed with water.

Properties: A basic solution tastes bitter. A basic solution feels slippery. They will turn red litmus paper blue. Strong bases can also damage the skin.

So, what are bases?

Like acids, when bases dissolve in water, they ionize.

This means that they split apart into the ions that make up the base.

NaOH Na+ + OH-

Note: Not all bases contain OH-. Some will react with water to form the hydroxide ion

NH3 + H20 NH4+ + OH-

How do bases work?

These work in a way that is similar to acids.

Strong bases cause a high concentration of OH- ions in the solution.

Weak bases cause a low concentration of OH- ions in the solution.

Strong and Weak Bases

Like acids, bases are corrosive and can damage living tissues

Wear safety goggles, gloves, and a lab apron!

Base Safety

How do determine if something is an acid or a base?

How do we measure acid and base concentration or strength?

What’s next?

Read pages 293-297.

Homework

Using Indicators with Acids and Bases

You can determine if a substance is an acid or base by using an indicator.

INDICATOR - A substance that changes color in the presence of an acid or a base.

Indicators measure the level of hydronium ions. This level determines if a substance is acidic or basic.

Detecting Acids and Bases

Cabbage juice can be used as an indicator.

Litmus paper is a common indicator. Litmus strips are small pieces of paper that are treated with a substance that changes color when exposed to acids and bases

An acid turns blue litmus paper red A base turns red litmus paper blue

Indicators

Litmus papers only function to let you know if a substance is acidic or basic.

They do not indicate strength or weakness of the solution.

To determine how acidic or basic a solution is, we use pH values.

pH is the measure of the concentration of hydronium ions in a solution.

More specific indicators

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

ACIDIC BASIC

NEUTRAL

The pH Scale

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

ACID BASE

NEUTRAL

The pH Scale

Ion

Con

cen

trati

on

Ion

Con

cen

trati

on

pH Scale

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neu

tral

P

ure

H2O

[H+] [OH-]

Acids Bases

Stronger Weaker Weaker Stronger

Acid – substance that produces H+ ions in aqueous

solution

Base – substance that produces OH-

ions in aqueous solution

Question #1Lemon juice has a pH of 2.2. Is it an acid or a base?

Which does it contain, hydronium ions or hydroxide ions?

Question #2Detergents such as Tide have a pH of about 10. Is Tide an acid or a base?

Which does it contain, hydronium ions or hydroxide ions?

Question #3 Seawater has a pH of 8.2. Is seawater an acid or a base?

Which does it contain, hydronium ions or hydroxide ions?

Question #4The inside of your mouth has a pH of 7. Is it an acid or a base?

Question #5How do you think we came up with the term “acid rain”?

Read pages 297-300

Homework