Notes On Acids And Bases

Notes on Acids and Bases

General Definitions |Properties |Water Dissociation |pH |Strength of Acids & Bases |Acid & Base Reactions |Titrations |Models of Acids |

1. General Definitions:
Acid: a substance which when added to water produces hydrogen ions [H+].
Base: a substance which when added to water produces hydroxide ions [OH-].

2. Properties:
Acids:
  · react with zinc, magnesium, or aluminum and form hydrogen (H2(g))
  · react with compounds containing CO32- and form carbon dioxide and water
  · turn litmus red
  · taste sour (lemons contain citric acid, for example) DO NOT TASTE ACIDS IN THE LABORATORY!!
Bases:
  · feel soapy or slippery
  · turn litmus blue
  · they react with most cations to precipitate hydroxides
  · taste bitter (ever get soap in your mouth?) DO NOT TASTE BASES IN THE LABORATORY!!

3. Water dissociation: H2O(l) → H+(aq) + OH-(aq)
equilibrium constant, KW = [H+][OH-] / [H2O]
Note: water is not involved in the equilibrium expression because it is a pure liquid, also, the amount of water not dissociated is so large compared to that dissociated that we consider it a constant
Value for Kw = [H+][OH-] = 1.0 x 10-14
Note: The reverse reaction, H+(aq) + OH-(aq) → H2O(l) is not equal to 1 x 10-14
[H+] for pure water = 1 x 10-7
[OH-] for pure water = 1 x 10-7
Definitions of acidic, basic, and neutral solutions based on [H+]
  · acidic: if [H+] is greater than 1 x 10-7 M
  · basic: if [H+] is less than1 x 10-7 M
  · neutral: if [H+] if equal to 1 x 10-7 M
Example 1: What is the [H+] of a sample of lake water with [OH-] of 4.0 x 10-9 M? Is the lake acidic, basic, or neutral?
Solution: [H+] = 1 x 10-14 / 4 x 10-9 = 2.5 x 10-6 M
Therefore the lake is slightly acidic
Remember: the smaller the negative exponent, the larger the number is.
Therefore:
  · acid solutions should have exponents of [H+] from 0 to -6.
  · basic solutions will have exponents of [H+] from -8 on.
Example 2: What is the [H+] of human saliva if its...