1. Acids and Bases
Chapter 10

2. Acids
The term acid comes from the Latin word acidus, which means “sour”
Acids taste sour, conduct electric current, and are corrosive
Vinegar, citrus fruits, toilet bowl cleaners, and carbonated beverages

3. Acids
Acids are essential to digestion and they play an important role in the chemical industry
85 billion pounds of sulfuric acid is produced annually in the U.S.—sulfuric acid is used to produce fertilizers, detergents, paint dyes, plastics, pharmaceuticals, storage batteries, iron, and steel

4. Bases Bases are characterized by their bitter taste and slippery feel
They are not slippery themselves; rather, they cause skin oils to transform into slippery solutions of soap
Reactions involving baking soda, ashes containing potassium carbonate, soap, drain cleaners

5. Bases
Most commercial preparations for unclogging drains are composed of sodium hydroxide, NaOH, a strong base
The U.S. manufactures about 25 billion pounds of NaOH for use in the production of chemicals in the pulp and paper industry
Solutions containing bases are called alkaline, derived from the Arabic word for ashes, al- qali

6. Brønsted-Lowry Definition
When acids and bases react with water, they ionize, or form ions
An acid is any chemical that donates a hydrogen ion, H+ (proton donor)
A base is any chemical that accepts a hydrogen ion (proton acceptor)

7. The Hydronium Ion
When acids react with water, the H+ attaches to water (a base in this reaction)
This results in 3 hydrogen atoms bound to 1 oxygen atom = hydronium ion, H3O+
Hydronium atoms give acids their properties

8. The Hydroxide Ion When bases react with water, water is the acid
Water donates a hydrogen to the base forming a hydroxide ion, OH-

9. The Lewis Definition
A more general and inclusive definition of acids and bases that relates acid/base behavior to molecular structure
Defines an acid as an electron pair acceptor, and a base as an electron pair donor
Does not involve H+

10. Neutralization
Reactions between an acid and a base are called neutralization reactions
If equal concentrations and volumes of the acid and base are mixed, all of the hydronium and hydroxide will react to form water
If the concentrations or volumes are not equal, the resulting product may be slightly acidic or basic, and water will not be formed

11. Formation of Salts
The remaining ions (positive from the base, negative from the acid) in the reaction will form a salt
Salt: any ionic compound formed from the reaction between an acid and a base
Generally, salts are far less corrosive than the acids and bases from which they are formed
Corrosive chemicals have the ability to disintegrate a material or wear away its surface

12. Formation of Salts Examples of salts include:
NaCN: Sodium cyanide—deadly poison
KNO3: Potassium nitrate—used as a fertilizer and formulation of gunpowder
CaCl2: Calcium chloride—used to de-ice roads
NaF: Sodium fluoride—used in toothpaste to prevent tooth decay

14. Strong Acids
In general, the stronger the acid, the more readily it donates a positive charge, usually a hydrogen ion
If water is added to an acid and almost all of the acid is converted to the hydronium ion, H3O+, then it is a strong acid
There are 7 strong acids
Hydrochloric acid (HCl), Hydrobromic acid (HBr), Hydroiodic acid (HI), Nitric acid (HNO3) Chloric acid (HClO3) Sulfuric acid (H2SO4) Perchloric acid (HClO4)

15. Weak Acids
Weaker acids have a lesser tendency to donate hydrogens to water, therefore the acid remains and hydronium ions are not formed
This means there are only a very few ions, so there is not much of an electrical current
In contrast, when a strong acid is dissolved in water, there are many ions formed, so there is a large electrical current

16. Strong Bases
A stronger base will more readily accept a positive charge, usually a hydrogen ion
Strong bases allow the flow of a large electrical current
There are 8 strong bases:
Lithium hydroxide (LiOH), Sodium hydroxide (NaOH), Potassium hydroxide (KOH), Rubidium hydroxide (RbOH), Cesium hydroxide (CsOH), Calcium hydroxide (Ca(OH)2), Strontium hydroxide (Sr(OH)2), Barium hydroxide, (Ba(OH)2)

17. Weak Bases Do not readily accept a hydrogen ion
Do not allow a large flow of electrical current
Ammonia, NH3, and water are common weak bases
Concentration is the most important factor in determining if strong/weak acids/bases are dangerous
Very concentrated ammonia can burn you even though it is a weak base
Very dilute hydrochloric acid won’t be as threatening as if it were a concentrated solution

18. Amphoteric Solutions
Amphoteric: A substance that is as likely to behave as an acid as it is a base
Water is amphoteric – it the ability to react with itself
Acid – water molecules donate hydrogens to neighboring water molecules
Base – water accepts the hydrogen ion
The reaction forms hydronium and a hydroxide ions, which react together to re-form water

19. Neutral Solutions
In a neutral solution, the amount of hydronium ions equals the amount of hydroxide ions
Pure water is an example of a neutral solution
In pure water, the concentration of both hydronium ions and hydroxide ions equals 1x10-7
“concentration of hydronium ions” can be written as: [H3O+]
“concentration of hydroxide ions” can be written as: [OH-]

20. Acidic Solutions
In an acidic solution, the hydronium ion concentration is greater than the hydroxide ion concentration
[H3O+] > [OH-]
Acidic solutions are made by adding acid to water—always add acid to water, never add water to acid, doing so will cause the water to boil very quickly and will spray hot acid

21. Basic Solutions
In a basic solution, the hydroxide ion concentration is greater than the hydronium ion concentration
[OH-] > [H3O+]
A basic solution is made by adding a base to water

22. pH Scale
The pH scale is a numeric scale used to express the acidity of a solution
Mathematically, the pH is equal to the negative of the base-10 logarithm of the hydronium ion concentration
pH = -log[H3O+]
Since the hydronium concentration of water is 1x10-7, the pH of water is equal to –log 1x10-7 = 7

23. pH Scale Acidic solutions have a pH of less than 7
The more acidic a solution is, the greater its concentration of hydronium ions and the lower its pH
Basic solutions have a pH that is greater than 7
The more basic a solution is, the smaller its concentration of hydronium ions is and the higher its pH

24. Calculating pH What is the pH of a 2.4 x 10-3 M H3O+?
pH = -log 2.4 x 10-3
pH = 2.6
What is the pH of a 5.92 x 10-5 M H3O+?
pH = -log 5.92 x 10-5
pH = 4.23
Which is more acidic?

25. Rainwater
Rainwater is naturally acidic—one source of its acidity is from carbon dioxide
There are about 810 billion tons of CO2 in the atmosphere from natural resources, like volcanoes and decaying organic matter, and human activities
Water in the atmosphere reacts with carbon dioxide to form carbonic acid
CO2 + H2O  H2CO3
Carbonic acid lowers the pH of water—CO2 in the atmosphere makes rain water have a pH of about 5.6

26. Acid Rain
Acid rain is the term used for rain that has a pH lower than 5
Created when airborne pollutants, such as sulfur dioxide, are absorbed by atmospheric moisture

27. Acid Rain
SO2 is converted to SO3, which reacts with water to form sulfuric acid
2 SO2 + O2  2 SO3
SO3 + H2O  H2SO4
Sulfuric acid is much stronger than carbonic acid
Rain with carbonic acid erodes land
Rain with sulfuric acid can erode metal, paint, and other exposed surfaces

28. Acid Rain
In the Midwestern U.S., the ground contains large amount of calcium carbonate (limestone), which is a basic compound and will neutralize the acid rain before damage is done
Long-term solution is to prevent sulfur dioxide from entering the atmosphere

29. Acid Rain
In northeastern U.S. and other regions, the effects of acid rain are greater because the ground does not contain a lot of limestone
A solution to the damaging effects of acid rain is called liming—the pH of lakes and rivers is increased by adding calcium carbonate

30. Indicators
Indicators are substances that change color in the presence of whatever they are testing for (there are many different indicators that can check for many different substances)
Indicators change color because of Le Chatelier’s Principles

31. Acid/Base Indicators
Acid/base indicators will change color when there is a change in pH
The universal indicator solution (phenolphthalein, bromothymol blue, and methyl red dissolved in ethanol and water) will change colors at each integral pH value (1, 2, 3, … 14)

32. Other pH indicators
Litmus and phenolphthalein are indicators

33. Buffer Solution
A buffer solution is any solution that resists large changes in pH
They work by containing two components: one component neutralizes any added base and the other component neutralizes any added acid
Effective buffer solutions are made by mixing a weak acid with a salt of the weak acid
Example: mixing acetic acid, C2H4O2, with sodium acetate, NaC2H4O2

34. Connections to our Lives
Our blood is a buffered solution—the pH needs to stay between 7.35 and 7.45
If the pH of our blood goes above or below this range, it can kill us
A blood pH above 7.45 is called alkalosis
A blood pH below 7.35 is called acidosis