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Acids and Bases

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General Properties

  • Acid (Latin) acidus
  • Acids are generally sour
  • Bases – alkaline
  • Bases are generally bitter
  • Bases feel slippery – many household cleaners
    • Slippery because they react with the fats in your skin.

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General Properties

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  • Generally toxic, especially in large quantities of concentrated solutions.
  • Can cause chemical burns. (corrosive)

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Indicators

  • Many acids and bases are colorless and odorless.
  • Indicators – molecular substances that change color when they come into contact with acids and bases.
  • Indicators include – cabbage juice, pH paper, litmus paper, universal indicator, phenolphthalein, etc.

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Indicators

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  • Common color changes:
    • Cabbage juice - acid = pink/red,

base = green/yellow neutral = purple

    • Litmus paper – acid = red, base = blue

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    • What range of numbers does the pH scale cover?

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    • What are the pH numbers for acids and bases?

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Chemical Makeup of Acids and Bases

  • Both are dissolved in water.
  • Acids produce hydrogen ions. H+
  • Bases produce hydroxide ions. OH-

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Acid Base Theories

  • Arrhenius Theory of Acids and Bases
  • Swedish chemist – Svante Arrhenius
  • Acid is a substance that adds H+, to an aqueous solution.
  • Base is a substance that adds OH- to an aqueous solution.
  • Aqueous = dissolved in water

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Acid Base Theories - Bronsted-Lowry

Danish chemist - Johannes Bronsted

English chemist - Thomas Lowry

  • Explains how bases w/o an OH- ion behave.
  • Acid is a substance that can donate a proton to another substance.
  • Base is a substance that can accept a proton from another substance.

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Acid Base Theories (B-L cont’.)

  • Example: Ammonia NH3
  • NH3(g) + H2O(l) →NH4+(aq) + OH- (aq)
  • Dissolved ammonia really consists of ammonium and hydroxide ions. Many times referred to as ammonium hydroxide.

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Strong and Weak Acids/Bases

  • Strong acids - dissociate completely in solution
  • Examples - HCl, nitric acid - HNO3, sulfuric acid - H2SO4, and hydrobromic acid - HBr
  • Good conductors of electricity.
  • Weak acids - only dissociate partially
  • Examples - formic acid - HCOOH, acetic acid -CH3COOH, and phosphoric acid H3PO4

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Strong and Weak Acids/Bases

  • Strong bases - dissociate completely
  • Examples - Sodium Hydroxide NaOH, Barium hydroxide Ba(OH)2
  • Weak bases - dissociate partially
  • Examples - ammonia NH3, and aniline C6H5NH2

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pH and H+ Relationship

  • pH = -log[H+]
  • Each time the H+ concentration changes by a factor of 10, the pH number changes by 1 unit.

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Molarity

[H+]

pH

1.0M HCl

1.0 x 100

0

0.1M HCl

1.0 x 10-1

1

0.01M HCl

1.0 x 10-2

2

0.001M HCl

1.0 x 10-3

3

0.0001M HCl

1.0 x 10-4

4

0.00001M HCl

1.0 x 10-5

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pH and OH- Relationship

  • [H+][OH-] = 1.0 x 10-14
  • The above formula is for any aqueous solution.

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pH and OH- Relationship

Molarity

[OH-]

[H+]

pH

water

1.0 x 10-7

1.0 x 10-7

7

0.00001M NaOH

1.0 x 10-5

1.0 x 10-9

9

0.0001M NaOH

1.0 x 10-4

1.0 x 10-10

10

0.001M NaOH

1.0 x 10-3

1.0 x 10-11

11

0.01M NaOH

1.0 x 10-2

1.0 x 10-12

12

0.1M NaOH

1.0 x 10-1

1.0 x 10-13

13

1.0M NaOH

1.0 x 100

1.0 x 10-14

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