1. Section 2.5—Characteristics of Acids and Bases
Objectives:
investigate the characteristics of acids & bases
distinguish between strong & weak acids & bases
distinguish between concentration & strength
explain the pH scale and use of indicators

2. Characteristics of Acids & Bases
Produce H3O+1 (hydronium
ion) in water
Produce OH-1 (hydroxide
ion) in water
Tastes sour
May sting or burn on contact
Tastes Bitter
React with active metals to
form hydrogen gas
Feels slippery
Turn blue litmus paper pink
Turns pink litmus paper blue

3. Acid Strength

4. Review of how acids produce ions-
water
acid
Hydrogen cation with some anion

5. Review of how acids produce ions- +1 H O

6. Review of how acids produce ions- +1 H O
Hydronium ion
Anion

7. Strong versus Weak Acids
How many hydronium ion – anion pairs can you find? - + - 3 +
How many intact (whole) acid molecules can you find? + - 1
Strong acid
Most of the acid molecules have donated their H+1 to water

8. Strong versus Weak Acids+
How many hydronium ion – anion pairs can you find? 1
How many intact acid molecules can you find? - 3
Weak acid
Only a few of the acid molecules have donated their H+1 to water

9. Strong versus Weak Acids
A strong acid is an acid that dissociates (comes apart) and ionizes (forms ions)almost completely in water.
A weak acid is an acid that dissociates and ionizes only slightly in water.

10. Concentrated versus Dilute Acids

11. A Note About Solutions
We saw in previous slides how an acid compound combines with water to form a hydronium ion and an anion. When this occurs, the acid is really an acid solution.
Solutions are homogeneous mixtures. There is a even mixing of the 2 parts throughout the mixture.
The 2 parts are called the solute – the substance that is dissolved – and the solvent – the substance that does the dissolving.

12. Concentrated versus Dilute Solutions
solvent
solute
Dilute
Not as many solute (what’s being dissolved) particles
Concentrated
More solute (what’s being dissolved) particles

13. Concentrated versus Dilute Acids
A concentrated acid will have a lot of the acid compound mixed into the water.
A dilute acid will not have a lot of the acid compound mixed into the water.

14. Concentration vs. Strength

15. Combinations of Concentration & Strength
Concentrated
Dilute
Strong
A lot of acid added & most dissociates
Not much acid added, but most of what’s there dissociates
Weak
A lot of acid added, but most stays together (does not dissociate)
Not much acid added and most of what is there stays together

16. Other notes
All of these same ideas about strength and concentration apply to bases as well
Many people think all acids are dangerous and all bases are more safe but . . .
Vinegar is an acid we eat…some acids are safe!
Sodium hydroxide is a very caustic base…not all bases are less harmful than acids!
The stronger an acid or base is (and the more concentrated it is), the more dangerous it is for you!!

17. pH

18. pH Scale
Is a scale to measure acidity (concentration of hydronium ions) 1 14
Highly acidic
Very basic (not acidic)
neutral 7
Chapter 6 will give more detail about how pH is calculated!

19. pH
Neutral Substances
These are substances that are not considered to be an acid or a base. They have a pH around 7.
Acidic Substances
These substances have a pH LESS THAN 7. In fact, the lower the pH, the greater the concentration of hydronium ions. The lower the pH, the more ACIDIC the substance is considered.

20. pH
Basic Substances
These substances have a pH GREATER THAN 7. In fact, the higher the pH, the lower the concentration of hydronium ions. The higher the pH, the more BASIC the substance is considered.

21. Ways to measure pH Indicators change color based on pH
Liquid indicators – various indicators change colors at different pH’s
Universal indicator – a combination of liquid indicators to produce a “rainbow” changing colors at several pH’s
Paper Indicators
Paper with a liquid indicator on it (Litmus paper or pH paper)
pH meters or pH probes
Electronically determine pH and give a read-out

22. Common pH indicators – pg. 56
This picture © 1998 David Dice

23. pH of common substances
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
Urine
6.6
Bile
6.9
Saliva 7
Blood
7.4
Eggs
7.8
0.1M NH3 (aq)
11.1
0.1M NaOH 13
Which substance is most acidic? least?
Which substance is most basic? least?
Is bread acidic or basic? eggs?
Is any substance is neutral?