Acids and Bases

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Acids and Bases
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pH Scale

• pH scale numbered from 0 to 14, measures
  acidity and alkalinity (how acidic or basic a
  solution is)

Neutral
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Strengths of Acids and Bases

• The lower the pH the STRONGER the acid
• More hydrogen ions (H)in solution
• The higher the pH the STRONGER the base
• More hydroxide ions (OH-) in solution

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I. Acid-Base Models

• A) Arrhenius Acids and Bases
• Acids substances contain hydrogen and form H
  ions in aqueous solution
• Example -
• HCl H (aq) Cl- (aq)

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• 2. Bases substances contain hydroxide (OH)
  ions and form OH ions in aqueous solution
• NaOH Na (aq) OH (aq)

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• Problem with this model some acids and bases
  dont fit Arrhenius definitions
• Example Is NH3 an acid or a base?
• It is not likely that NH3 will lose a H, but it
  will produce OH ions in water, like this
• NH3 H2O NH41 (aq) OH1 (aq)

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• B) Brønsted-Lowry Acids and Bases
• 1. Acids hydrogen ion (proton) donors
• 2. Bases hydrogen ion (proton) acceptors do
  not necessarily contain OH
• NH3 H2O NH41 (aq) OH1 (aq)

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II. Auto-Ionization of Water

• In pure water, 2 out of every billion molecules
  transfer a proton and break apart into ions
  according to this reaction
• HOH ? H OH-

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• B) Ion-product constant for water (Kw)
• Kw H OH- 1.0 x 10-14 M2
• this value is a constant that can be used to
  determine acidity or alkalinity (basic) of a
  solution
• In neutral solutions, H OH-
• in acidic solutions, H gt OH-
• in basic solutions, OH- gt H

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Ion Concentration Examples

• H OH- 1 x 10-14 M2
• 1. What are the ion concentrations of a 0.000453M
  solution of HCl?
• is the solution an acid or base?
• 2. What are the ion concentrations of a 0.00250M
  solution of KOH?
• Acid or base?

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pH CalculationspH stands for power of Hydrogen

• pH logH
• Example What is the pH of a solution with a
  hydrogen ion concentration of 3.5 x 10-9 M?
• pH log H
• pH -log3.5 x 10-9
• pH 8.46

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How do I get back from pH to ion concentrations?

• H antilog (-pH)
• Whats antilog?
• 2nd function of log key (10x)

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• H antilog (pH)
• Example Determine the concentration of
  hydrogen ions in a solution with a pH of 3.5
• H antilog (3.5)
• H 10(3.5)
• H 3.16 x 10-4 M

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What is redox?

• Any chemical process in which elements experience
  a change in charge is an oxidation-reduction
  reaction (redox reaction)
• Redox reactions involve a transfer of electrons.
• Oxidation involves losing electrons
• Reduction involves gaining electrons
• LEO the lion says GER

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Rules for Assigning Charges

• All unbonded elements have a charge of 0
• Oxygen is always a -2 (for this class)
• Fluorine is always a -1
• Hydrogen is always 1 (for this class)
• Alkali metals are always 1
• Alkaline earth metals are always 2
• Aluminum is always 3
• Neutral compounds have a charge of 0
• The sum of the charges of the elements in a
  polyatomic ion equals the charge of the
  polyatomic ion.

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Example

• Identify if the following equations are redox
  reactions or not. For each redox reaction,
  determine which element is oxidized and which
  element is reduced.
• Ca(OH)2 2 HCl ? CaCl2 2 H2O
• CH4(g) 2 O2(g) ? CO2(g) 2 H2O(g)
• 2 Al(s) 3 CuCl2(aq) ? 2 AlCl3(aq) 3 Cu(s)

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Neutralization

• When a strong acid reacts with a strong base to
  form a salt and water.
• Example
• 2 NaOH H2SO4 ? Na2SO4 2 H2O

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Precipitation Reactions

• Precipitate solid that is produced when two
  solutions are mixed together
• These reactions are double-replacement reactions
  (switch dance partners) that form solids
• Example
• 2 KI (aq) Pb(NO3)2 (aq) ? PbI2 (s) 2 KNO3 (aq)

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Titration Problems

• Titration using a solution of known
  concentration to determine the concentration of
  an unknown solution
• Equivalence Point the point when there are
  equal amounts of moles of the acid and base
• Indicator substance that changes color when the
  reaction is complete, end point.