1. Acids and Bases

2. History of Acids and Bases
In the early days of chemistry chemists were organizing physical and chemical properties of substances. They discovered that many substances could be placed in two different property categories:
Substance A
Sour taste
Reacts with carbonates to make CO2
Reacts with metals to produce H2
Turns blue litmus pink
Reacts with B substances to make salt water
Substance B
Bitter taste
Reacts with fats to make soaps
Do not react with metals
Turns red litmus blue
Reacts with A substances to make salt and water
Arrhenius was the first person to suggest a reason why substances are in A or B due to their ionization in water.

3. Definitions Acids – produce H+ Bases - produce OH- Acids – donate H+
Bases – accept H+
Acids – accept e- pair
Bases – donate e- pair
Arrehenius
only in water
Bronsted-Lowry
any solvent
Lewis
used in organic chemistry,
wider range of substances

4. Arrhenius Theory
The Swedish chemist Svante Arrhenius proposed the first definition of acids and bases.
(Substances A and B became
known as acids and bases)
According to the Arrhenius model:
“acids are substances that dissociate in water to produce H+ ions and bases are substances that dissociate in water to produce OH- ions”
NaOH (aq)  Na+ (aq) OH- (aq) Base
HCl (aq)  H+ (aq) Cl- (aq) Acid

5. General properties ACIDS Taste sour Turn litmus
React with active metals – Fe, Zn
React with bases
BASES
Taste bitter
Turn litmus
Feel soapy or slippery (react with fats to make soap)
React with acids
blue to red
red to blue

6. What is an acid?
An acid is a solution that has an excess of H+ ions. It comes from the Latin word acidus that means "sharp" or "sour".
The more H + ions, the more acidic the solution.

7. Properties of an Acid Tastes Sour Conduct Electricity
Corrosive, which means they break down certain substances. Many acids can corrode fabric, skin,and paper
Some acids react strongly with metals
Turns blue litmus paper red
Picture from BBC Revision Bites

8. Uses of Acids Acetic Acid = Vinegar
Citric Acid = lemons, limes, & oranges. It is in many sour candies such as lemonhead & sour patch.
Ascorbic acid = Vitamin C which your body needs to function.
Sulfuric acid is used in the production of fertilizers, steel, paints, and plastics.
Car batteries

9. What is a base? A base is a solution that has an excess of OH- ions.
Another word for base is alkali.
Bases are substances that can accept hydrogen ions

10. Properties of a Base Feel Slippery Taste Bitter Corrosive
Can conduct electricity. (Think alkaline batteries.)
Do not react with metals.
Turns red litmus paper blue.

11. Uses of Bases
Bases give soaps, ammonia, and many other cleaning products some of their useful properties.
The OH- ions interact strongly with certain substances, such as dirt and grease.
Chalk and oven cleaner are examples of familiar products that contain bases.
Your blood is a basic solution.

12. Conjugate acid- compound formed when a base gains a hydrogen ion.
Conjugate base – compound formed when an acid loses a hydrogen ion.

13. The Bronsted-Lowry Concept
Conjugate pairs
HCl Cl-
CH3COOH CH3COO-
NH NH3
HNO3 NO3-

14. Neutralization HCl + NaOH  NaCl + HOH
In general: Acid Base  Salt + Water
All neutralization reactions are double displacement reactions.
HCl NaOH  NaCl HOH

15. Salts NEUTRALIZATION REACTIONS: acid + base -----> salt + water
Back to objectives
NEUTRALIZATION REACTIONS:
reaction between an acid and a base to form a salt and water
acid + base > salt + water
HCl + Na(OH) -----> NaCl + H(OH)
H(NO3) + Na(OH) -----> Na(NO3) + H(OH)

16. For pure water: (H+) = (OH-) = 10-7M
Does pure water conduct electrical current?
Water is a very, very, very weak electrolyte.
H2O  H OH-
For pure water: (H+) = (OH-) = 10-7M
This is neutrality and at 25oC is a pH = 7.
water

17. Let’s examine the behavior of an acid, HA, in aqueous solution.
CHM 101
Let’s examine the behavior of an acid, HA, in aqueous solution.
Sinex HA

18. 100% dissociation of HA HA H+ Strong Acid A-
Would the solution be conductive?

19. Partial dissociation of HA
Weak Acid A-
Would the solution be conductive?

20. At any one time, only a fraction of the molecules are dissociated.
HA  H A- HA H+
Weak Acid A-
At any one time, only a fraction of the molecules are dissociated.

21. Strong and Weak Acids/Bases
Strong acids/bases – 100% dissociation into ions
HCl NaOH
HNO3 KOH
H2SO4
Weak acids/bases – partial dissociation, both ions and molecules
CH3COOH NH3

22. pH acid rain (NOx, SOx) pH of 4.2 - 4.4 in Washington DC area
1-14 scale for the chemists 2 3 4 5 6 7 8 9 10 11 12
acidic
(H+) > (OH-)
25oC
(H+) = (OH-)
distilled water
basic or alkaline
(H+) < (OH-)
normal rain (CO2)
pH = 5.3 – 5.7
fish populations
drop off pH < 6
natural waters pH =

23. Indicators Show a color change to identify an acid or base Types:
Litmus paper
Red – acid
Blue – base
Phenolphthalein (liquid)
Clear – acid, neutral
Pink – base

24. pH pH SCALE: Range of numbers from 0 to 14
Indicates acid, base, and neutral along with strength

25. pH Scale

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

27. Reactions with indicators
Acid color
Neutral color
Base color
Phenolphthalein
Colorless
Faint pink
Dark pink
Bromthymol blue
Yellow
Green
Blue
Litmus
Red
-----

28. pH paper
pH paper changes color to indicate a specific pH value.

29. What is an oxide?
An oxide is a compound of oxygen and another element.
Most oxides can be grouped into four types:
acidic oxides
basic oxides
amphoteric oxides
neutral oxides

30. Acidic oxides Oxides of non-metal
Acidic oxides are often gases at room temperature.

31. Acidic oxides React with water to produce acids. Example:
sulphur trioxide + water sulphuric acid
SO3 + H2O H2SO4

32. Acidic oxides React with bases and alkalis to produce salts Example:
carbon dioxide + sodium hydroxide sodium carbonate + water
CO2 + 2NaOH Na2CO3 + H2O

33. Examples of acidic oxides
Formula
Acid Produced with Water
sulphur trioxide
SO3
sulphuric acid, H2SO4
sulphur dioxide
SO2
sulphurous acid, H2SO3
carbon dioxide
CO2
carbonic acid, H2CO3
phosphorous(V) oxide
P4O10
phosphoric acid, H3PO4

34. Basic oxides Calcium oxide (quicklime) Oxides of metal
Basic oxides are often solids at room temperature.
Most basic oxides are
insoluble in water.
Calcium oxide (quicklime)

35. This is a neutralisation reaction
Basic oxides
React with acids to produce salts and water only.
Example:
Magnesium oxide + hydrochloric acid magnesium chloride + water
MgO + 2HCl MgCl2 + H2O
This is a neutralisation reaction

36. Examples of basic oxides
Formula
magnesium oxide
MgO
sodium oxide
Na2O
calcium oxide
CaO
copper(II) oxide
CuO

37. Amphoteric oxides Zinc oxide Oxides of metal
Can behave as acidic oxides
or as basic oxides
Zinc oxide

38. Neutral oxides
Non-metals that form oxides that show neither basic nor acidic properties.
Insoluble in water.

39. Examples of neutral oxides
Formula
water
H2O
carbon monoxide CO
nitric oxide NO

40. When life goes either way amphoteric (amphiprotic) substances
Acting like
a base
Acting like an acid
HCO3-
+ H+
- H+
H2CO3
CO3-2
accepts H+
donates H+

41. pH The biological view in the human body acidic basic/alkaline saliva1 2 3 4 5 6 7 8 9 10 11
saliva
blood
urine
gastric juice
vaginal fluid
pancreatic juice
bile
cerebrospinal fluid
Tortora & Grabowski, Prin. of Anatomy & Physiology, 10th ed., Wiley (2003)

42. Show how water can be amphoteric.