Warm-up 1/9/13

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Warm-up 1/9/13

• What do you know about acids and bases?
• Daily Objectives TSW-
• Begin acid/base concepts.
• Review for final

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Unit 11

• Acids and Bases

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Acid vs Base

• All aqueous solutions contain H and OH- ions.
• Relative amounts determine whether the solution
  is acid, base, or neutral
• Acid soln more H (Hydronium ion)
• Basic soln- more OH-
• Neutral- equal amounts of each

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Which solution is Acidic? Basic? Neutral???
H
OH-
H
OH-
OH-
H
Basic
Acidic
Neutral
Solution
Solution
Solution
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Arrhenius Model

• Acid is a substance that contains hydrogen and
  ionizes to produce hydrogen ions in aqueous solns
• Base is a substance that contains a hydroxide
  group and dissociates to produce a hydroxide ion
  in aqueous solns
• Shortcomings- NH3 (Exception)

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Acids and Bases

• Produce OH- ions in water
• Have a bitter taste and a slippery feel
• Break down fats and oils
• Formula ends with OH
• Poisonous and corrosive to skin
• pH greater than 7

• Produce H ions in water
• Have a sour taste
• Break down metals
• Formula starts with H
• Poisonous and corrosive to skin
• pH less than 7

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Brønsted-Lowry Model

• Acid- hydrogen ion donor
• Base- hydrogen ion acceptor
• HX (aq) H20 (l) ? H30 (aq) X- (aq)

Base
ConjugateAcid
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Conjugates

• Conjugate Acid
• Species produced when a base accepts a hydrogen
  ion from an acid
• Conjugate Base
• Species that results when an acid donates a
  hydrogen ion to a base
• Conjugate acid- base pair
• Consists of 2 substances related to each other by
  donating and accepting of a single H

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Conjugates

• HF H2O ? H3O F- (H3O Conjugate acid)
• (F- Conjugate base)
• NH3 H20 ? NH4 OH- (NH4 Conjugate acid)
• (OH- Conjugate base)
• Amphoteric- substances that can act as both acids
  and bases
• Monoprotic- HCl, HF
• Polyprotic- H2SO4, H3PO4

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Acid Strength

• Strong acids ionize completely
• Weak acids- do not ionize completely
• Ka
• HCN H2O ? H3O CN-
• Ka

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Practice Problems

• Write an ionization equation and acid ionization
  constant expression for Nitrous Acid.
• HNO2
• HNO2 H2O ? H3O NO2-
• Ka

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One More Practice Problem

• Write an ionization equation and acid ionization
  constant expression for Chlorous Acid.
• HClO2
• HClO2 H2O ? H3O ClO2-
• Ka

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Base Strength

• Strong Bases- completely dissociate into metal
  ions and hydroxide ions
• Weak bases- partially dissociate
• Base ionization constant
• Kb

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Practice Problems

• Write ionization equations and base
  ionization constant expressions for the carbonate
  ion.
• CO32-
• CO32- H2O ? HCO3- OH-
• Kb

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One More Practice Problem

• Write ionization equations and base
  ionization constant expressions for the hydrogen
  sulfite ion.
• HSO3-
• HSO3- H2O ? H2SO3 OH-
• Kb

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pH

• Measure of H ions in soln
• pH -logH
• Acidic solutions have a pH below 7
• Basic solutions have a pH above 7
• pH 7 is neutral
• Change of 1 pH unit represents a tenfold change.
  (exponential)

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pOH

• Measures concentration of OH- ion
• pOH - log OH-
• pH pOH 14.00

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Practice Problems

• Calculate the pH and pOH of aqueous solutions
  having the following ion concentrations.
• OH- 6.5 x 10-6
• pOH -logOH- pH 14.00 pOH
• pOH -log6.5 x 10-6 pH 14.00 5.19
• pOH -log 6.5 log 10-6 ph 8.81
• pOH -0.81 (-6)
• pOH 5.19

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One more, one more time!

• Calculate the pH and pOH of aqueous solutions
  having the following ion concentrations.
• H 3.6 x 10-9
• pH -logH pOH14.00 pH
• pH -log3.6 x 10-9 pOH14.00-8.44
• pH -log 3.6 log 10-9 pOH5.56
• pH -0.56 (-9)
• pH 8.44

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Buffers

• A buffer is a mixture of a weak acid and its
  conjugate base OR, a weak base and its conjugate
  acid.
• This mixture resists changes in pH.
• The amount of acid or base a buffer can absorb
  without significant change in pH is called the
  buffer capacity.

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Neutralization Reactions

• When an acid is added to a base, the end products
  are always salt and water. (neutral)
• A salt is defined as the neutral end product of
  an acid/base reaction.
• ACID BASE ? SALT WATER
• H2S Ca(OH)2 ? CaS H2O
• What is wrong with this equation???

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Balance the final equation!
H2S Ca(OH)2 ? CaS
H2O 1 Ca 1 1 S 1 4 H 2 2 O 1
H2S Ca(OH)2 ? CaS 2 H2O
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Neutralization Reactions
Try another example Acid Base ?
Salt Water H2SO4 NaOH ?
Na2SO4 H2O 1 Na 2 1 SO4 1 3
H 2 1 O 1 H2SO4 2 NaOH ? Na2SO4
2 H2O
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Take it one step further
Sulfurous acid and sodium hydroxide yields sodium
sulfite and water. H2SO3 NaOH ?
Na2SO3 H2O 1 Na 2 1 SO3 1 3 H 2
1 O 1 H2SO3 2NaOH ? Na2SO3
2H2O
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One Last Step

• Hydrosulfuric acid and calcium hydroxide yields
  what???
• H2S Ca(OH)2 ?
• One product will always be water.
• H2S Ca(OH)2 ? H2O
• The other product will be the ion of the base
  bonded with the ion of the acid.
• H2S Ca(OH)2 ? 2H2O CaS

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pH Indicators

• A chemical substance that changes color in the
  presence of an acid and/or a base.
• 1) pH paper Dip the paper, match color to scale
  on vial to determine numeric pH.
• pHlt7 acid, pHgt7 base, pH 7 neutral
• 2) Litmus Dip one red and one blue paper.
• Red stays red, blue turns red ? Acid
• Blue stays blue, red turns blue ? Base
• Red stays red, blue stays blue ? Neutral

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pH Indicators
3) Bromthymol Blue Add a few drops of
bromthymol blue to the substance. If the blue
color turns to yellow ? Acid If the blue color
stays blue ? Base 4) Phenolphthalein Add a
few drops of phenolphthalein to the substance. If
the clear liquid turns to pink ? Base If the
clear liquid remains clear ? Acid