Intro to acids and bases

1
Intro to acids and bases

• Chapter 16 sections 16.1-16.3

2
Review

• What makes something an acid?
• What makes something a base?
• Give examples of acids and bases?
• What is the way we measure the strength of an
  acid or a base?

3
Properties of Acids and Bases

• Acids have very distinct properties
• They taste sour
• Lemon, vinegar
• They are corrosive to metal
• Bases also have distinct properties
• They are bitter
• Feel slippery
• Hand soap

4
Properties of Acids and Bases cont

• 1st discoveries of Acids Bases made by Svante
  Arrhenius.
• Arrhenius Model
• Acids produce H ions
• HCl ? H Cl-
• Bases produce OH- ions
• NaOH ? Na OH-

5
Properties of Acids and Bases cont

• Bronsted Lowry Model improved upon Arrhenius
  model
• Before only OH ions could be base
• In this model, the acid is a PROTON (H) DONOR,
  and the base is a PROTON ACCEPTOR
• HA H2O ? H3O A-
• Acid Base Conjugate
  acid Conjugate base
• Acid is proton donor (H)
• Base is proton acceptor (H)
• Conjugate Acid (H3O)
• Conjugate Base (A-)

6
Properties of Acids and Bases cont

• Wait! How can water act as a base?
• Remember that when you draw the Lewis dot
  structure of water that the oxygen has 2 lone
  pairs of electrons?
• When an acid (something that has a H ion) is
  reacted with it, then that extra H can attach to
  one of the lone pairs.
• This is called a hydronium ion

7
Properties of Acids and Bases cont

• Lets try to name the parts of a Bronsted-Lowry
  acid base reaction!
• HCl H2O ? H3O Cl-
• Name the acid, base, conjugate acid, conjugate
  base
• Answer
• Acid is proton donor (HCl)
• Base is proton acceptor (H2O)
• Conjugate Acid (H3O)
• Conjugate Base (Cl-)

8
Properties of Acids and Bases cont

• A conjugate acid-base pair consists of the two
  substances that are related to each other by
  donating and accepting a single proton

9
Properties of Acids and Bases cont

• HClO4 H2O ?
• What would be the conjugate acid pair?
• What would be the conjugate base pair?
• HClO4 H2O ? H3O ClO4-
• Acid- Conjugate base pair HClO4 ? ClO4-
• Base- Conjugate acid pair H2O ? H3O

10
Acid Strength

• Can the reaction go backwards?
• H3O A- ? HA H2O
• Yes, it depends on the strength of the acid
  base
• If the reaction goes in both directions it is
  represented with double arrows
• HA H2O ? H3O A-
• Acid Base Conjugate acid
  Conjugate base
• A strong acid is one in which the forward
  reaction predominates
• A weak acid is one in which the reverse reaction
  predominates

11
Acid Strength Cont
12
Relationship of acid strength and conjugate
base strength for the dissociation reaction.
13
Acid Strength

• There are various ways to describe the strength
  of an acid
• Sulfuric acid can actually supply 2 protons, this
  is called a diprotic acid
• Most acids are called oxyacids which means the
  acidic hydrogen is attached to an oxygen atom
• Organic acids contain a carbon backbone

14
Water can act as an acid or a base

• Amphoteric substance can behave as either acid
  or base
• Ionization of water
• H2O H2O ? H3O OH-
• Actually, its not at a perfect equilibrium. It
  prefers to be H2O
• Thus the arrow is both directions, but the sizes
  of the arrow would be more like this
• ? and ?
• In pure water only tiny amounts of OH and H3O
  exist
• Sometimes H3O is written as H

15
Flashback to last unit

• If we know that.
• NaCl ? Cl- Na
• And that 1M NaCl means 1M Cl- and 1M Na
• Then when applying this to the dissociation of
  water the same rule applies
• H2O H2O ? H3O OH-
• If the concentration of H3O is 1.0 x 10-7 M,
  what is the concentration of OH-?
• Answer 1.0 x 10-7 M

16
What you need to know

• Anytime you see
• H2O H2O ? H3O OH-
• You know that water is amphoteric (acting as acid
  and base)
• Concentration of H30 OH- 1.0x 10-7 M
• Multiplying the concentration of H3O x OH- will
  always equal 1.0 x 10-14 M

17
What you need to know cont.

• A neutral solution, where H30 OH-
• An acidic solution, where H3O gt OH-
• A basic solution, where H3O lt OH-
• But
• Try one
• If H3O concentration is 1.0 x 10-8 M what is the
  solution?
• H x OH- 1.0 x 10 -14
• 1.0 x 10-8 x OH-1.0 x 10 -14
• OH 1.0 x10-6

18
Homework

• Read Pages 502-513. Problems 1-5 on page 513
  problems 9 and 22 on page 532-533