Acids, Bases, and Salts

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Acids, Bases, and Salts

• Chapter 18

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Properties of Acids and Bases

• When dissolved in distilled water, they look the
  same
• Taste
• Acid developed from the latin term acidus (sour
  or tart)
• Citric acid, lactic acid, carbonic acid,
  hydrochloric
• Bases taste bitter
• Soap is an example of a base

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Properties of Acids and Bases

• Touch
• Dilute acids do not cause painful burns, but if
  an open wound is exposed, then a sting is felt
• Dilute bases do not sting (except in eyes)
• Typically feel smooth or soothing in low
  concentrations
• The higher the concentration for either acids or
  bases can result in painful burns

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Properties of Acids and Bases

• Reactions with Metals
• Acids react with several metals including Mg, Zn,
  Fe, Al
• See activity series p. 295
• Bases do not react with metals

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Properties of Acids and Bases

• Electrical Conductivity
• Both acids and bases are good electrolytes (good
  conductors of electricity)
• Distilled water is a poor conductor, but if an
  acidic or basic solution is made, then the
  solution is quite conductive
• Electrolyte substance that ionizes when
  dissolved in water

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Properties of Acids and Bases

• Indicator substance that turns 1 color in an
  acidic solution and a different color in a basic
  solution
• Litmus is the most common indicator.
• Acids turn blue litmus paper RED or PINK
• Bases turn red litmus paper BLUE
• Phenolphthalein is another example which changes
  colors at a specific level of acidity or basicity

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Properties of Acids and Bases

• Neutralization Reaction reaction between an
  acid and a base
• If the proper amounts of acid and base are added,
  they will completely neutralize each other.
• Based on MOLES
• Two products are always formed
• H2O and an ionic salt

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Arrhenius Definition

• Swedish chemist Svante Arrhenius
• Developed an operating definition of acids and
  bases according to the ions they produce when
  dissolved in water
• Acids dissociate in water to produce hydrogen
  (H ions)
• HCl, HNO3, H2SO4
• Bases dissociate in water to produce hydroxide
  (OH- ions)
• NaOH, Ca(OH)2

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Dissociation Examples

• Mg(OH)2 (aq) ?
• HBr (aq) ?
• HC2H3O2 (aq) ?
• CuOH (aq) ?

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Neutralization examples

• NaOH (aq) HCl (aq) ?
• Mg(OH)2 (aq) HBr (aq) ?
• HC2H3O2 (aq) CuOH (aq) ?

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Arrhenius Definition Limitations

• Restricts acids and bases to water solutions
• Acid and base reactions can occur in the gas
  phase or can be dissolved in other solvents
• Chemicals such as ammonia (NH3) are bases, yet
  they do not have an OH- in the formula.
• So, a new definition had to be developed

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Bronsted-Lowry Definition

• Acid substance that can donate H ions
• Base substance that can accept H ions
• What is an H ion? How many protons, neutrons,
  and electrons?
• SoH can also be referred to as a ____.
• Acid substance that can donate _____.
• Base substance that can accept ____.

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Polyprotic?

• Protic refers to protons
• How many protons does a monoprotic acid donate?
• How many protons does a diprotic acid donate?
• H3PO4 is an example of a _____ acid.

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Hydronium Ions

• H ions are very attracted to the electrons of
  surrounding water molecules.
• H H2O ? H3O
• H3O hydronium ion

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ID the B-L Acids and Bases

• HCl(g) H2O (l) ? H3O (aq) Cl- (aq)
• NH3 (g) H2O (l) ? NH4 (aq) OH- (aq)

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Amphoterism

• A substance that can act as an acid or a base
  depending on the circumstances.
• See previous slide.

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Conjugate Acid-Base pairs

• Technically, almost all acid-base reactions are
  reversible
• NH3 (g) H2O (l) NH4 (aq) OH- (aq)
• Conjugate means coupled or joined
• Conjugate is used to describe the acid or base
  in the reverse reaction.

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Determining the Strengths of Acids and Bases

• Vinegar contains 1M acetic acid
• Spilling this on your skin has no great effect
• Spilling 1 M HCl on your skin is a cause for
  concern
• Why?
• The strength of an acid or base is dependent upon
  the degree to which they dissociate.

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Strong vs Weak

• HCl is a strong acidso it is assumed that it
  dissociates completely
• HCl(g) H2O (l) ? H3O (aq) Cl- (aq)
  lots lots
• Acetic acid is a weak acidso not very much
  product is producedit is reversible
• HC2H3O2 (aq) H2O (l) H3O (aq)
  C2H3O2- (aq) little little

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Strong and Weak Acids

• Strong Acids
• HCl
• HBr
• HI
• HNO3
• H2SO4

• Weak Acids
• HC2H3O2
• HCN
• HNO2
• HF
• H2CO3

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Strong and Weak Bases

• Strong Bases
• CaO
• NaOH
• KOH
• Ca(OH)2

• Weak Bases
• NH3
• CO32-
• PO43-

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Acid Dissociation Constant

• Generic Weak Acid, formula HA
• HA (aq) H2O (l) H3O (aq) A- (aq)
• How would the Keq be written?
• We also call this Ka, or the acid dissociation
  constant.
• What does a large Ka mean? Small Ka?

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Base Dissociation Constant

• Generic base, formula B
• B (aq) H2O (l) HB (aq) OH-
  (aq)
• How would the Keq be written?
• We also call this the Kb, or the base
  dissociation constant.
• What does a large Kb mean? Small Kb?

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Identifying Acids

• Binary Acids
• Contain hydrogen and one other element (usually
  group 6A or 7A)
• HCl
• HF
• H2Se
• H2S

• Ternary Acids (Oxyacids)
• Contain hydrogen, oxygen, and one other element
• H2SO4
• HNO3
• H3PO4

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Identifying Bases

• Most of the bases we will work with will have the
  OH- ion in the formula.
• NaOH
• Mg(OH)2
• Otherwise you should recognize ammonia (NH3) as a
  base even though it does not have an OH in the
  formula.

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Naming Acids

• Typically, the name of the acid comes from the
  name of the ion it produces when it dissociates.
• Rule 1 If the name of an anion ends in -ide, the
  name of the acid that produces it includes the
  name of the anion, a hydro- prefix, and an ic
  ending.
• Cl- is the chloride ion. The acid which produces
  it is HCl. Hydro- is placed in front, chlor is
  the root, and ic is the ending.
• Hydro chlor ic acid hydrochloric acid

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Naming Acids

• Rule 2 If the name of an anion ends in ate, the
  name of the acid that produces this anion has NO
  prefix (no hydro), but it does have an ic
  ending.
• NO3- is nitrate.
• Nitr is the root and ic is the ending.
• Nitr ic acid nitric acid

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Naming Acids

• Rule 3 If the name of an anion ends in ite, the
  name of the acid that produces this anion has NO
  prefix and has an ous ending.
• SO32- is the sulfite ion.
• Sulf is the root and ous is the ending.
• Sulfur ous Sulfurous acid
• Notesulfurous, not sulfic

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Bases

• Name them just like all ionic compounds
• NaOH sodium hydroxide
• Ca(OH)2 calcium hydroxide
• Mg(OH)2
• Cu(OH)
• Cu(OH)2

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Try these acids

• Name
• Phosphoric acid
• Nitrous acid
• Hydrofluoric acid
• Chloric acid

• Formula
• H2CO3
• H2Se
• HIO4