The Chemistry of Acids and Bases

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The Chemistry of Acids and Bases
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Acid and Bases
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Acid and Bases
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Acid and Bases
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Some Properties of Acids

• Produce H (as H3O) ions in water (the
  hydronium ion is a hydrogen ion attached to a
  water molecule)
• Taste sour
• Corrode metals
• Electrolytes
• React with bases to form a salt and water
• pH is less than 7
• Turns blue litmus paper to red Blue to Red
  A-CID

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Some Properties of Bases

• Produce OH- ions in water
• Taste bitter, chalky
• Are electrolytes
• Feel soapy, slippery
• React with acids to form salts and water
• pH greater than 7
• Turns red litmus paper to blue Basic Blue

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Some Common Bases
Formula Name Common Name

• NaOH
• KOH
• Ba(OH)2
• Mg(OH)2
• Al(OH)3

sodium hydroxide lye
potassium hydroxide liquid soap
barium hydroxide stabilizer for plastics
magnesium hydroxide MOM Milk of magnesia
aluminum hydroxide Maalox (antacid)
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Acid Nomenclature
Binary ?
Ternary
An easy way to remember which goes with
which In the cafeteria, you ATE something ICky
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Acid Nomenclature Flowchart
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Acid Nomenclature Review

• HBr (aq)
• H2CO3
• H2SO3

? hydrobromic acid
? carbonic acid
? sulfurous acid
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Try these

• Hydroiodic Acid

• HI (aq)
• HCl (aq)
• H2SO4
• HNO3
• H2CO3

• Hydrochloric Acid

• Sulfuric Acid

• Nitric Acid

• Carbonic Acid

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Try these

• Hydrobromic Acid

• HBr (aq)
• HCN (aq)
• H2SO3
• HClO4
• CH3OOH

• Cyanic Acid

• Sulfurous Acid

• Perchloric Acid

• Acetic Acid

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Acid/Base definitions

• Definition 1 Arrhenius (traditional)
• Acids produce H ions (or hydronium ions H3O)
• Bases produce OH- ions
• (problem some bases dont have hydroxide ions!)

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Arrhenius acid is a substance that produces H
(H3O) in water
Arrhenius base is a substance that produces OH-
in water
NaOH H2O ? OH- Na H2O
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Acid Base Definitions

• Definition 2 BrønstedLowry
• Acids proton donor
• Bases proton acceptor
• A proton is really just a hydrogen atom that
  has lost its electron!

PDA (proton donated acid)
BAD (BrønstedLowry acid donates)
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ACID-BASE THEORIES
A Brønsted-Lowry Acid is a proton donor A
Brønsted-Lowry Base is a proton acceptor
The Brønsted definition means NH3 is a Base in
water and water is itself an Acid
Conjugate Base
Conjugate Acid
Acid
Base
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Conjugate Pairs
Conjugate Acid the remaining ion or molecule
that can re-accept the proton and act as a
base
Conjugate Base the species that is formed when
a Brønsted-Lowry base gains a proton.
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Acids Base Definitions
Definition 3 Lewis

• Lewis acid - a substance that accepts an electron
  pair

Lewis base - a substance that donates an electron
pair
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Lewis Acids Bases

• Formation of hydronium ion is an excellent
  example.

• Electron pair of the new O-H bond originates on
  the Lewis base.

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Acids Base Definitions Summary
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SOME DEFINITIONS

• Amphoteric - A substance that can act as either
  an acid or a base, e.g., H2O, HCO3-
• Polyprotic acid or base - An acid or base that
  can donate or accept more than one proton or
  hydroxide, e.g., H3PO4, H2CO3, H4EDTABa(OH)2,
  Al(OH)3

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Strong and Weak Acids/Bases
The strength of an acid (or base) is determined
by the amount of IONIZATION.

• Generally divide acids and bases into STRONG or
  WEAK

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Strong and Weak Acids/Bases
STRONG ACID

• HNO3 (aq) H2O(l) --gt H3O(aq) NO3-(aq)
• HNO3 is about 100 dissociated in water.

HNO3, HCl, HBr, HI, H2SO4 and HClO4 are among the
only known strong acids.
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Strong and Weak Acids/Bases

• Weak acids are much less than 100 ionized in
  water.
• One of the best known is acetic acid CH3COOH

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Strong and Weak Acids/Bases

• Strong Base 100 dissociated in water.
• NaOH (aq) ---gt Na (aq) OH- (aq)

Other common strong bases include KOH and
Ca(OH)2. CaO (lime) H2O --gt Ca(OH)2
(slaked lime)
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Strong and Weak Acids/Bases

• Weak base less than 100 ionized in water
• One of the best known weak bases is ammonia
• NH3(aq) H2O(l) ? NH4(aq) OH-(aq)

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Other Weak Bases
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The pH scale is a way of expressing the strength
of acids and bases. Instead of using very small
numbers, we just use the NEGATIVE power of 10 on
the Molarity of the H (or OH-) ion.Under 7
acid 7 neutralOver 7 base
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pH of Common Substances
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1) Solution A H3O 5.89 x 10-7 pH
?  2) Solution B H3O 4.365 x 10-12 pH
?  3) Solution C H3O 1.05 x 10-4 pH
?  4) Solution D H3O 1.00 x 10-6 pH ?
Determine the pH of the following H3O
concentrations
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1) Solution A H3O 5.89 x 10-7 pH
6.23  2) Solution B H3O 4.365 x 10-12 pH
11.36  3) Solution C H3O 1.05 x
10-4 pH 3.98  4) Solution D H3O 1.00 x
10-6 pH 6.00
Determine the pH of the following H3O
concentrations
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pH meter

• Tests the voltage of the electrolyte
• Converts the voltage to pH
• Very cheap, accurate
• Must be calibrated with a buffer solution

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Calculating the pH

• pH - log H
• (Remember that the mean Molarity)
• Example If H 1 X 10-10pH - log 1 X
  10-10
• pH - (- 10)
• pH 10
• Example If H 1.8 X 10-5pH - log 1.8 X
  10-5
• pH - (- 4.74)
• pH 4.74

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pH calculations Solving for H

• If the pH of Coke is 3.12, H3O ???
• Because pH - log H3O then
• - pH log H3O
• Take antilog (10x) of both sides and get
• 10-pH H3O
• H3O 10-3.12 7.59 x 10-4 M
• to find antilog on your calculator, look
  for Shift or 2nd function and then the log
  button

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pOH

• Since acids and bases are opposites, pH and pOH
  are opposites!
• pOH is useful for changing bases to pH.
• pOH looks at the perspective of a base
• pOH - log OH-
• Since pH and pOH are on opposite ends,
• pH pOH 14

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pH
H
OH-
pOH
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The pH of rainwater collected in a certain region
of the northeastern United States on a particular
day was 4.82. What is the H ion concentration
of the rainwater?
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pH testing

• There are several ways to test pH
• Blue litmus paper (red acid)
• Red litmus paper (blue basic)
• pH paper (multi-colored)
• pH meter (7 is neutral, lt7 acid, gt7 base)
• Universal indicator (multi-colored)
• Indicators like phenolphthalein
• Natural indicators like red cabbage, radishes

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pH indicators

• Indicators are dyes that can be added that will
  change color in the presence of an acid or base.
• Some indicators only work in a specific range of
  pH
• Once the drops are added, the sample is ruined
• Some dyes are natural, like radish skin or red
  cabbage

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The pigment in red cabbage juice is anthocyanin,
which changes color from red in acid solution to
purplish to green in mildly alkaline solution to
yellow in very alkaline solution.
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Other pH Indicators
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• Determine the pH to the tenth and ion
  concentration of the following unknown solution
  given the color of each indicator
• q       Phenolphthalein - colorless
• q       Universal indicator red-orange
• q       Bromcresol Green yellowish green

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• Determine the pH to the tenth and ion
  concentration of the following unknown solution
  given the color of each indicator
• q       Alzarin Yellow R yellow
• q       Phenolphthalein - pink
• q       Thymolphthalein blue

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• Determine the pH to the tenth and ion
  concentration of the following unknown solution
  given the color of each indicator
• q      Methyl Orange yellowish orange
• q       Chlorphenol Red yellow
• q       Bromthymol Blue yellow
• q       Bromcresol Green blue

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ACID-BASE REACTIONSTitrations

• H2C2O4(aq) 2 NaOH(aq) ---gt
• acid base
• Na2C2O4(aq) 2 H2O(liq)
• Carry out this reaction using a TITRATION.

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Setup for titrating an acid with a base
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Titration

• 1. Add solution from the buret.
• 2. Reagent (base) reacts with compound (acid) in
  solution in the flask.
• Indicator shows when exact stoichiometric
  reaction has occurred. (Acid Base)
• This is called NEUTRALIZATION.