Section 2.5—Characteristics of Acids and Bases

Now that we know what acids are, how do they act?

Characteristics of Acids & Bases

BasesAcids

Produce H3O+1 (hydronium ion) in water

Produce OH-1 (hydroxide ion) in water

Tastes sour Tastes Bitter

React with active metals to form hydrogen gas

Feels slippery

Strength versus Concentration

Review of how acids produce ions

H

OH

H -

water acid

Hydrogen cation with some anion

Review of how acids produce ions

H

OH

H -+1

Review of how acids produce ions

H

OH

H+1 -

Hydronium ion Anion

Strong versus Weak Acids

+

++

-

-

-

Strong acidMost of the acid molecules

have donated the H+1 to water

How many hydronium ion – anion pairs can you find?

How many intact acid molecules can you find?

3

1

Strong versus Weak Acids

+

-

Weak acidOnly a few of the acid

molecules have donated the H+1 to water

How many hydronium ion – anion pairs can you find?

How many intact acid molecules can you find?

1

3

Concentrated versus Dilute

solute solvent

Lower concentration

Not as many solute (what’s being dissolved) particles

Higher concentration

More solute (what’s being dissolved) particles

Combinations of Concentration & Strength

DiluteConcentrated

A lot of acid added & most

dissociates

Not much acid added, but most of

what’s there dissociates

A lot of acid added, but most stays together

Not much acid added and most of what is there stays

together

Strong

Weak

All of the same ideas apply to bases as well (concentration and strength)

Many people think all acids are dangerous and all bases are more safeVinegar is an acid we eat…some of them are

safe!Sodium hydroxide is a very caustic base…not all

of them are less harmful than acids!The stronger and acid or base is (and the more

concentrated it is), the more dangerous it is for you

Other notes

pH

Is a scale to measure the acidity of a sample

pH Scale

1 14

Highly acidic Very basic (not acidic)

neutral

7

Chapter 6 will give more detail about how pH is calculated!

Indicators change color based on pHLiquid indicators – various indicators change colors at

different pH’sUniversal indicator – a combination of liquid indicators to

produce a “rainbow” changing colors at several pH’s

Paper IndicatorsPaper with a liquid indicator on it (Litmus paper or pH

paper)

pH meters or pH probesElectronically determine pH and give a read-out

Ways to measure pH

Common pH indicators

This picture © 1998 David Dice

pH of common substances

SUBSTANCE PH

0.1M HCl 1

Stomach contents

2

Vinegar 2.9

Soda pop 3

Grapes 4

Beer 4.5

Pumpkin pulp 5

Bread 5.5

Intestinal contents

6.5

Milk 6.5

Urine 6.6

Bile 6.9

Saliva 7

Blood 7.4

Eggs 7.8

0.1M NH3 (aq) 11.1

0.1M NaOH 13