Acids and Bases

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Acids and Bases

• Text Chapter 8
• Previous knowledge Naming Acids and Bases (Gr.
  11)

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Acid and Bases

• Acid

• Base

• Sour
• Electrolytes
• Gritty feel
• pH 0 - 6.9
• Blue litmus red
• React with bases to form a salt and water
• Put H into solution
• Made by reaction of oxides and water and binary
  covalent molecules and water

• Bitter
• Electrolytes
• Slippery feel
• pH 7.1 14
• Red litmus blue
• React with acids to form a salt and water
• Put OH- into solution
• Made by metallic oxides and water

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Acid and Base Names

• Acids
• Contains one or more hydrogen atoms
• General formula
• HnX
• H hydrogen atom
• n number of hydrogen atoms (subscript)
• X monoatomic or polyatomic anion

HCl H2SO4
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Acid and Base Names

• When the name of the anion ends in ide (X), the
  acid is a binary acid, and the prefix is hydro
  and the ending is ic
• When there is a polyatomic ion, that makes up
  (X), the acid is a ternary acid. If the ion ends
  in ite, the ending for the acid is ous
• When the polyatomic ion ends in ate, the ending
  for the acid is ic

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Acid and Base Names

• Hint If the name of the anion is ate, and the
  acid is ic, one less oxygen, the acid is ous,
  one more less oxygen, the acid is prefix hypo
  and ending is ous
• If there is one more oxygen than the ate
  polyatomic ion, the name is, prefix per and
  ending ic
• Some organic acids, you just have to memorize the
  name. Ex. Ethanoic Acid CH3COOH

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Acid and Base Names

• HCl
• H2SO4
• H2SO3
• HCN
• HClO3
• HClO4
• HClO
• H3PO4

Cl- - chloride
Binary hydro stem - ic
Hydrochloric acid
SO4 -2 - Sulfate
Ternary stem - ic
Sulfuric Acid
Sulfurous Acid
SO3-2 - sulfite
Ternary stem - ous
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Acid and Base Names

• Bases
• Named the same as ionic compounds
• Some you just have to memorize (ie. Ammonia)

Positive ion cation ()
Negative ion anion (-)
NaOH
Sodium hydroxide
Magnesium hydroxide Aluminum hydroxide
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Acid Base Theories

• Arrhenius Acids and Bases
• Hydrogen containing compounds that ionize (ions
  wanderers to produce H are acids
• Hydroxide containing compounds that produce OH-
  ions in solution are called bases
• Not all substances that contain hydrogen atoms
  or hydroxide will be acidic or basic. It depends
  on electronegativity and polarity between the
  acidic / basic unit and the bonded atoms.

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Acid Base Theories

• Bronsted Lowry Acid and Bases
• Acid hydrogen ion donor
• Base hydrogen ion acceptor
• Substance that accepts the hydrogen is the
  conjugate acid
• Substance that donates the hydrogen is the
  conjugate base
• Used for those exceptions that cannot be
  explained by Arrhenius
• Truer theory as a naked hydrogen ion is very
  unlikely and unstable. Hydronium ion is most
  likely

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Acid Base Theories

• Water can behave as both a conjugate base and
  acid (can accept and donate)
• Called Amphoteric substance (behave as an acid
  and a base)

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Strengths of Acids and Bases

• Based upon structure
• Greater the EN difference, the greater the
  ionization and dissociation, means the more
  product is formed, and more H or OH- goes into
  solution
• Therefore, stronger acid and base (Keq greater
  than 1)
• First ionization is the strongest
• Second and subsequent ionizations are weaker.
  (p.607)

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Acid Base Theories

• The number of hydrogens will determine whether it
  is monoprotic, diprotic or triprotic acids.
• Structure will determine the strength of the
  acid.
• Rule the greater the EN difference, the greater
  the polarity, the greater the dissociation
  (ionization) and strength of the acid or base.
• Rule For ternary acids, if the Oxygens out
  number the hydrogens by more than 2, the acid
  will be strong
• Greater net pull, according to the first rule.

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Strengths of Acids and Bases

• Keq for an acid is called Ka, and is the measure
  of how much of the acid ionizes (H or H3O and
  X) and how much stays together (HnX)
• Keq for a base is called Kb, and is the measure
  of how much OH- and ion is in solution and how
  much stays together.

HX H X- H2XOy H H XOy-
M(OH)z M Z( OH-)
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Strengths of Acids and Bases

• The amount that dissociates, or ionizes, is in
  equilibrium with the acid that stays as a whole
• If the Keq is greater than 1, it favours
  product
• For Acids and Bases, the Keq greater than 1,
  means it dissociates 100, and all of the
  reactant (acid or the base) goes to ions.

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Strengths of Acids and Bases
H2SO4 H HSO4 -2
I 2.0 0 0
C 2.0 -2.0 0 2.0 02.0
E 0 2.0 2.0

• For example
• H2SO4 Ka 1.00 x 103
• H2SO4 H H SO4-
• Therefore, if the concentration of the acid is
  2.0 M, the concentrations of ions will be

Therefore, the concentration of the hydronium ion
is 2.0 M.
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Strengths of Acids and Bases

• Therefore, when a strong acid or base
  dissociates, 100 turns into ions.
• What would be the OH- for a sodium hydroxide
  solution with a molarity of 0.5 M?

Solution sodium hydroxide is a strong base,
therefore, it dissociates 100 NaOH Na
OH- 0.5 M O.5 M 0.5 M
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Strengths of Acids and Bases
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Strengths of Acids and Bases

• What about weak acids and bases?
• We need to solve for the concentrations of ions,
  using Ka or Kb values because they do not
  dissociate 100
• Ka or Kb values are less than 1, favouring the
  acid or base to stay together and little ionize.
• They may only dissociate 50 or 10, leaving the
  majority of the acid or base as a whole and
  very little in ion form

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Strengths of Acids and Bases

• Example
• What is the H concentration in a 1.0 M
  solution of carbonic acid? (Ka 4.3 x 10-7)

Hint Look at the Ka value. It is less than 1.
Therefore, it will not dissociate 100 and is a
weak acid. We need to use equilibrium to
determine the concentration of the H.
Note In your text, the Keq expression is
written using Bronsted /Lowry. You can use
either, as long as you remember that there are
some exceptions in which the ionization cannot be
shown using Arrhenius. Also, the Keq expression
uses water, then omits it. Keep in mind, water
always has a concentration of 1 M. Concentration
of water?!!!!
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Strengths of Acids and Bases

• Why are we finding the H or OH-?

pH power of hydrogen or potential of hydrogen
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Hydrogen Ions and pH

• Based upon water
• Highly polar
• Made up of hydronium ion and hydroxide ion
• Self Ionization of water (Kw)

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Hydrogen Ions and pH

• Each ion has a value of 1 x 10 -7 M, which, when
  multiplied together forms the Keq or Kw, which is
  1 x 10 -14
• Both are equal to each other in terms of their
  concentrations, and therefore form a neutral
  substance (pH 7)
• If the concentration of H is greater than 1 x 10
  -7 M, the solution is acidic (ie. More H and
  less OH-), since all solutions are in water.
• If the concentration of H is less than 1 x 10 -7
  M, the solution is basic (ie. Less H and more
  OH-), since all solutions are in water.

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Hydrogen Ions and pH

• pH potential hydrogen
• pH scale is based upon the H found in a
  solution.
• If the H is greater than 1 x 10 -7 M, the
  solution will be acidic and the pH will be less
  than 7.
• If the H is less than 1 x 10 -7 M, the
  solution will be basic and the pH will be greater
  than 7.
• pH is the negative log of the hydrogen ion
  concentration.

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pH Scale
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Measuring pH Acid Base Indicators

• Indicator usually a weak acid that accepts
  hydrogen ions, and in doing so, changes its
  chemical structure, which facilitates a colour
  change.
• Litmus changes from red to blue at pH of 7, or
  1 x 10 -7 M
• Bromothymol Blue is yellow below 1 x 10 -7 M,
  green at 1 x 10 -7 M, and blue over 1 x 10 -7 M
• Phenopthlalein changes color at a pH of 7-9 (the
  hydrogen ion concentration of 1 x 10 -7 M to 1 x
  10 -9 M)

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Measuring pH Acid Base Indicators

• HIn (aq) H(aq) In-(aq)
• Acid Form Base Form
• Color 1 Color 2

OH-
H
The change is caused by the removal of a
hydronium ion to form the Base form and the
addition of a hydronium ion for the acid form.
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Measuring pH Acid Base Indicators

• Indicator papers are impregnated with the
  indicator solution and when exposed to the
  hydrogen ion, change color, depending on the
  concentration
• Universal Indicators show all pH levels. What do
  you think they are made up of?

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Neutralization Reactions and Titration

• If we have high levels of acid in our stomach, we
  take an antacid (base) to control it.
• In our small intestine, the acidic chyme, is
  neutralized by the bile (basic) to make sure we
  do not ulcerate our intestine
• Why does it neutralize?
• We make a salt and water, that does not
  necessarily work out to a pH of 7 (more later)
• We could bring the solution to a pH of 7.

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Neutralization Reactions and Titration

• H OH-
• 1 x 10-7 M 1 x 10-7 M
• Ex. If you react a strong acid and a strong
  base, the ions in solution will cancel each other
  out, producing a neutral solution. The products
  are always, regardless of the product pH, a salt
  and water.
• HCl(aq) NaOH(aq) NaCl(aq) H2O(l)

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Neutralization Reactions and Titration

• The point where the number of moles of hydronium
  ion equals the number of moles of hydroxide ion,
  is called the equivalence point. (not necessarily
  pH 7)
• Salt
• The compound formed by the cation of the base
  bonding with the anion of the acid.

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Neutralization Reactions and Titration

• Titration
• The process of adding a known amount of solution
  of known concentration to determine the
  concentration of another solution
• When the color changes, this is called the end
  point, which is the point of neutralization
• There is only salt and water at this point, if
  both were strong acids and bases.

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Neutralization Reactions and Titration

• Animation of Titration
• Lab Primer
• The idea is to calculate the concentration or
  number of moles for an unknown solution, using
  the equivalence point to determine neutralization

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Neutralization Reactions and Titration

• Titration Curves

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Salts

• Salts are the combination of the cation from the
  base and the anion from the acid and are the
  products of neutralization reactions
• Salts can be acidic, basic or neutral, depending
  on the strength of the acid and base that formed
  it.
• Buffers are an equilibrium condition which
  consists of the weak acid and conjugate base
  (salt) in solution, or a weak base and its
  conjugate acid (salt) keeping pH stable

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Salts

• Generally, if a strong acid reacts with a strong
  base, the resulting salt will be neutral (pH7)
  (ie. The equivalence point is 7)
• For salts formed from weak acids with a strong
  base, or weak bases with a strong acid, the salt
  will not be neutral
• This is called by salt hydrolysis, as the cations
  or anions from a dissociated salt remove or add
  hydrogen ions to water, creating either H, or
  OH- in solution

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Salts

• Another way to determine the acidity or basicity
  of a salt is to look at the net ionic equation
  and remembering that strong bases and acids
  dissociate 100, while weak acids and bases do
  not.
• In general
• Acidic salts produce positive ions that release
  protons into water
• Basic solutions produce negative ions that
  attract protons from water

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Salts
Strong Acid Strong Base Neutral solution
Strong Acid Weak Base Acidic Solution
Weak Acid Strong Base Basic Solution
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Buffers

• Buffer
• A substance in which the pH remains constant,
  when small amounts of acid or base is added.
• It contains the weak acid and one of its salts
  (anion conjugate base) or the weak base and one
  of its salts (cation conjugate acid)
• Pure water is not a buffer, as when you add acid
  (H) or base (OH-), the concentrations increase,
  changing the pH

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Buffers

• A buffer is like a sponge
• When hydrogen ions are added, they are absorbed
  by the negative ion, forming the whole weak
  acid, that does not dissociate 100, lowering the
  acidity, and raising the pH to neutral
• When hydroxide is added, they react with the
  acid to form the negative ion and water, lowering
  the basicity, and lowering the pH to neutral

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Buffers

• Animation of Buffering
• Common buffers, keep the pH at a stable level
• Ethanoic acid maintain pH 4.76
• Carbonic acid maintain pH 6.5 (blood)
• Ammonia maintain pH 9