1. Introduction to Acids and Bases

2. Introduction
Organisms are often very sensitive to the effect of acids and bases in their environment.
They need to maintain a stable internal pH in order to survive—even in the event of environmental changes.
Many naturally occurring biological, geological, and man-made chemicals are capable of stabilizing the environment’s pH.
This may allow organisms to better survive in diverse environments found throughout the earth.

3. Introduction Cont.
Acids and bases are a way of classifying compounds based upon what happens to them when you place them in water.
An acid is a substance that yields an excess of hydrogen ions when dissolved in water.
A base is a substance that yields an excess of hydroxide ions when dissolved in water.

5. Definitions of Acids and Bases
An acid is a substance that breaks into ions in an aqueous solution.
A Base (is a substance that breaks into ions in an aqueous solution.
Note: aqueous solution is any solution where is the solvent.

6. Common Acids
Vinegar (acetic or ethanoic acid)
Citric Acid

7. Characteristics of Acids
Sour taste (for edible acids)
May burn your skin
Turn litmus paper from blue to red.

8. Other Examples of Acids
HCl Hydrochloric Acid
H2SO4 Sulfuric Acid
CH3COOH Acetic Acid (Vinegar)

9. Common Bases
Ammonia

10. Characteristics of Bases
Bitter taste (for edible bases only)
Can be poisonous and corrosive.
Feels slippery
Turn litmus from red to blue.

11. Other examples of Bases
Sodium Hydroxide NaOH
Potassium Hydroxide KOH
Ammonia NH3

12. Three Definitions of Acids and Bases
Svante Arrhenius (Swedish 1887)
Bronsted- Lowry (Danish and English 1923 independently proposed definition)
Gilbert Lewis (American 1920’s)

13. Arrhenius Definition of Acids and Bases
Acids produce hydrogen ions (H+) in an aqueous solution, while bases produce hydroxide ion (OH-).
Acid: HCl (aq) H+ (aq) + Cl- (aq)
Base: NaOH(aq) Na+(aq) + OH-(aq)

14. Bronsted- Lowry Definition of Acids and Bases
An acid is a proton (H+) donor.
A base is a proton (H+) acceptor.
Example:
HF + H2O H3O+ + F-
Acid Base
H3O+ : hydronium ion

15. Lewis Definition of Acids and Bases
An acid accepts a pair of electrons.
A base donates a pair of electrons.
This is a more general definition than the previous two.
Example:
:NH3 + H+  NH4+

16. Three Models of Acids and Bases
Definition of Acid
Definition of Base
Arrhenius
H+ producer
OH- producer
Bronsted-Lowry
H+ donor
H+ acceptor
Lewis
Electron-pair acceptor
Electron-pair donor

17. Importance of WATER
Water acts as an acid and as a base. It is amphoteric

18. Acids A dilute acid has lots of water and a small amount of acid
A concentrated acid has lots of acid and not much water so must be handled carefully
A strong acid releases lots of H+
A weak acid releases fewer H+

19. The extent to which a compound is acidic or basic is measured by the pH scale.

20. Measuring acid strength?
To decide if something is an acid or a base we can use an indicator.
Litmus and Universal Indicator are examples of indicators.
They change colour depending on if they are in an acid or a base.

21. What is the pH scale?
The pH scale measures how acidic or basic a solution is.

22. Identifying Acids and Bases
Acids have a ph from 0-7
Lower pH value indicates a stronger acid.
Bases have a pH from 7-14
Higher pH value indicates a stronger base.

23. Did we Miss something?? What happens when the pH of a substance is 7?
Ans: A pH level of 7 indicates a Neutral Substance i.e: Water!

24. Why Learn about Acids & Bases?
What do you think is the pH level of NYC tap water?
The pH of a swimming pool must be checked periodically. Why?
Is it important for Lakes & Rivers to maintain a certain pH?

25. Situations in which pH is controlled
“Heartburn”
Planting vegetables and flowers
Fish Tanks and Ponds
Blood
Swimming pools

26. Acid Rain
Pollution in the air (sulfur dioxide, carbon dioxide, nitrogen dioxide) combines with water to form various acids. .

27. pH in the Digestive System
Mouth-pH around 7. Saliva contains amylase, an enzyme which begins to break carbohydrates into sugars.
Stomach- pH around 2. Proteins are broken down into amino acids by the enzyme pepsin.
Small intestine-pH around 8. Most digestion ends. Small molecules move to bloodstream toward cells that use them

30. Review

31. Acids Produce H+ (as H3O+) ions in water
Produce a negative ion (-) too
Taste sour
Corrode metals
React with bases to form salts and water

32. Bases Produce OH- ions in water Taste bitter, chalky Are electrolytes
Feel soapy, slippery
React with acids to form salts and water

33. pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335