1. The Chemistry of Acids and Bases

2. Objectives Define the following:
Acids
Bases
The pH scale
compare/ contrast properties of acids and bases
Describe common uses of acids and bases
Explain and write equations for the chemical reactions that occur between acids and bases

3. Acids
Acid – a chemical which easily “donates” (loses) a hydrogen ion (H+) when placed in an aqueous solution
Examples:
Carbonic Acid
Hydrochloric Acid
Stomach Acid
Battery Acid

4. Properties of Acids
Cause foods to taste tart or sour (vinegar – contains acetic acid)
React with metals to produce hydrogen gas
React with a base to produce an ionic salt and water
Found in many citrus foods
Form electrolytes when placed into water

5. Dissociation of an acid in water
An acid will dissociate (break apart) into H+ ions and negative ions when placed into water
Example: HCl (g) H+ (aq) + Cl- (aq)
H2O

6. When the acid dissociates into H+ ions and negative ions, some of the water molecules will bond with the H+ ions and form a Hydronium ion (H3O+)
The strength of Acids are actually measured by the amount of Hydronium ions they form when placed in water

7. Bases
Base – a chemical which easily “accepts” (gains) a hydrogen ion (H+) when placed in an aqueous solution
Examples:
Potassium Hydroxide
Magnesium Hydroxide
Ammonia

8. Properties of Bases Taste bitter Feel slippery
Will form electrolytes when placed in aqueous solutions
Found in many soaps and household cleaners

9. Dissociation of a base in water
A base will dissociate (break apart) into OH- ions and positive ions when placed into water
The OH- ions will then “accept” Hydrogen ions
Example: NaOH (s) Na+ (aq) + OH- (aq)
H2O

10. Acid – Base Chemical Reactions
A neutralization reaction will occur when an acid and a base are mixed in an aqueous solution:
Acid Base Salt Water
HCl (aq) NaOH (aq) NaCl (s) H2O
HNO3 (aq) + Mg(OH)2 (aq) Mg(NO3)2 (s) + H2O

11. The pH Scale Measures the relative strength of acids and bases
Range is from 0 – 14
0 = strongest acids
7 = neutral
14 = strongest bases

12. The pH scale is logarithmic
A solution with a pH value of 4 has 10 times as many H+ ions as a solution with a pH value of 5
A solution with a pH value of 3 has 100 times as many H+ ions as a solution with a pH value of 5

13. What is a buffer?
A buffer solution is a solution that will resist extreme changes in pH when mixed with a strong acid or a strong base
A buffer is usually a mixture of a weak acid and a weak base

14. Societal Issue: Acid Rain
Acid rain is rain that is acidic (has a pH between 5 and 6.5)
Is caused by air pollutants such as Sulfur dioxide and Nitrogen oxides
These pollutants react with the atmosphere, causing precipitation to be acidic
Societal Issue: Acid Rain

15. Effects of Acid Rain
Run- off from acid precipitation causes lakes and streams to become acidic
kills fish, plants, and other aquatic organisms
pollutes ground water
Destroys trees (forests)
Damages statues, buildings, etc.

16. Summary Acids = donate H+ ions Bases = accept H+ ions
Taste tart/ sour, found in many foods
Bases = accept H+ ions
Found in soaps/ cleaning products
Acid + Base = salt + water
The pH scale measures the strength of acids and bases