Acids and Equilibrum

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Acids and Equilibrum
Chapters 16-17
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• Acids

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A. Properties
ACIDS
BASES

• electrolytes ? electrolytes

• sour taste

• bitter taste

• turn litmus red

• turn litmus blue

• react with metals to form H2 gas

• slippery feel

• vinegar, milk, soda, apples, citrus fruits

• ammonia, lye, antacid, baking soda

ChemASAP
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The Arrhenius Model

• Acid produces hydrogen ions in aqueous solution
  
• Base produces hydroxide ions in aqueous
  solution

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Acids

• Acids have Hydrogen atom in them
• Give off H
• Examples
• HCl
• H2SO4
• Even H2O

HCl ? H Cl-
H2SO4 ? 2H SO4-2
H2O ? H OH-
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Bases

• Have OH (Called hydroxide) in them
• Examples
• NaOH
• Ca(OH)2
• Even H2O

NaOH ? Na OH-
Ca(OH)3 ? Ca 2OH-
H2O ? H OH-
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The Bronsted-Lowry Model

• Acid proton donor
• Base proton acceptor
• The general reaction for an acid dissolving in
  water is

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The Bronsted-Lowry Model

• Conjugate acid-base pair

Always in pairs acids need a base to accept
proton.
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The Bronsted-Lowry Model

• Water acts as a base accepting a proton from the
  acid.
• Forms hydronium ion (H3O)

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Water is amphoteric

• Can act as both acid and base
• Can produce both H
• And also OH-

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Monoprotic and Polyprotic

• Monoprotic - Give off only one H
• HCl
• HNO3
• even HC2H3O2
• Polyprotic - Give off more than one H
• H2SO3

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Acid Strength

• Strong acid completely ionized or completely
  dissociated

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Strong Acid

• HCl ? H Cl-
• Mostly H Cl- ions
• Very little HCl molecule in solution.

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Strength

• Strong Acid/Base
• 100 ionized in water
• strong electrolyte

HCl HNO3 H2SO4 HBr HI HClO4
NaOH KOH Ca(OH)2 Ba(OH)2
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B. Acid Strength

• Weak acid most of the acid molecules remain
  intact

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Acid Strength

• Common strong acids are

• Sulfuric acid, H2SO4
• Hydrochloric acid, HCl
• Nitric acid, HNO3
• Perchloric acid, HClO4

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Strength

• Weak Acid/Base
• does not ionize completely
• weak electrolyte

HF CH3COOH H3PO4 H2CO3 HCN
NH3
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Strong and Weak

• Strong and weak are not the same as Concentrated
  and dilute
• Strong means
• Concentrated means

Can a concentrated acid solution be weak?
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Water as an Acid and a Base

• Water is amphoteric it can behave as either an
  acid or as a base
• Ionization of water

• Concentration of hydronium and hydroxide are
  equal

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Acids and Bases
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PH

• Used to measure strength of an Acid or Base

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The pH Scale

• The p scale is used to express small numbers.
• pH ?log H

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The pH Scale
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The pH Scale

• Because the pH scale is a log scale based on 10,
  the pH changes by 1 for every power of 10 change
  in the H.

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B. pH Scale

0
14
7
INCREASING ACIDITY
INCREASING BASICITY
NEUTRAL
pH -logH3O
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pH Scale

• pH of Common Substances

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pH Scale
pH -logH3O pOH -logOH- pH pOH 14
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pH Scale

• Lower the pH means STRONGER the acid
• This means more H ions in solution
• This is the ion that makes acid act like an acid
• Each one unit change is 10 times stronger

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A. The pH Scale
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B. pH Scale

• What is the molarity of HBr in a solution that
  has a pH of 4.4?

Acidic
pH -logH 4.4 -logH -4.4
logH H3O 4.0 ? 10-5 M HBr
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Measuring pH

• Indicators substances that exhibit different
  colors in acidic and basic solutions

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Universal Indicator
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Measuring pH

• Other methods

• Indicator paper
• pH meter

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Mixing an acid and a base

• Neutralization Reaction

Acid Base ? Water and salt HCl NaOH
? H2O NaCl
neutral
Strong Acid Strong Base Strong Acid Weak
Base Weak Acid Strong Base Weak acid
weak base
slightly acidic
slightly basic
neutral
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Acid-Base Titrations

• Titration delivering a measured volume of a
  solution of known concentration into the solution
  being analyzed
• Titrant a standard solution
• Buret device used for accurate measurement of
  the delivery of a liquid
• Stoichiometric point (equivalence point) when
  just enough titrant has been added to react with
  all of the solution being analyzed

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Acid-Base Titrations

• Titration curve (pH curve) plot of the data (pH
  vs volume) for a titration

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Buffered Solutions

• Buffered solution resists a change in its pH
  when either and acid or a base has been added
• Presence of a weak acid and its conjugate base
  buffers the solution