Chapter 15
Acids and Bases

  1. Properties of Acids and Bases
    Foods with a sour taste - may be due to the presence of acids

    lactic acid

    acetic acid

    phosphoric acid

    citric acid

    malic acid

    tartaric acid

    bitter tasting --
    be careful about tasting any unknown substance

    household ammonia

    sodium hydroxide - lye

    milk of magnesia - magnesium hydroxide

    1. Acids
      common properties based on their aqueous solutions

      a) aqueous solution of acids have a sour taste -
      be careful about tasting any unknown substance

      b) acids change the color of acid-base indicators
      pH paper, blue litmus to red

      c) some acids react with active metals to release hydrogen gas
      e.g. Ba
      (s) + H 2 SO 4 ---> BaSO 4 + H 2

      d) acids react with bases to produce salts and water

      e) some acids conduct electric current

      1. Acid Nomenclature
        binary acid - definition

        hydrogen halides in water

        table 15-1 page 454

        hydro + root of halogen + ic + word acid

        oxyacid - definition

        Table 15-2 page 455

        know formulae of all of the -ic acids in table 15-2

        one more oxygen, add prefix per to name of ic acid

        one less oxygen, change suffix ic to ous

        two less oxygen, change suffix ic to ous and add prefix hypo

    2. Some Common Industrial Acids
      1. Sulfuric Acid
        Most commonly produced industrial chemical in the world

        Used in petroleum refinery and metallurgy and the manufacture of fertilizers

        The acid used in auto batteries

        Attracts water and used as a dehydration agent
      2. Nitric Acid
        Volatile, unstable liquid

        Stains proteins yellow

        Used in making explosives, many of which are nitrogen containing compounds

        Also used in making rubber, plastics, dyes and pharmaceuticals.

        Solution turns from colorless to yellow when left standing for long periods -- due to the decomposition to brown nitrogen dioxide gas.

      3. Phosphoric Acid
        phosphorus + nitrogen + potassium found in fertilizers

        most of this acid that is produced is used in fertilizers and animal feed

        has a pleasant but sour taste and is not toxic

        used as a flavoring agent in beverages and as a cleaning agent for dairy equipment

        also used in the manufacture of detergents and ceramics
      4. Hydrochloric Acid

        produced in the stomach as a digestive juice

        used to pickle iron and steel

        general cleaning agent in industry

        also used as muriatic acid
      5. Acetic Acid

        clear, colorless, pungent smelling liquid - glacial acetic acid

        pure acetic acid freezes at 17
        o C

        forms crystals in a cold room

        white vinegar - 4 to 8% acetic acid

        used in synthesizing chemicals used in the manufacture of plastics
        also used as a fungicide
    3. Bases

      a) bitter taste

      b) change the color of acid base indicators e.g. pH paper, red litmus to blue

      c) slippery feeling

      d) react with acids to produce salt + water (neutralization rxn)

      e) conduct electric current - ions in solution

    4. Arrhenius Acids and Bases

      Arrhenius acid - definition

      Arrhenius base - definition

      acids due to ionization

      bases usually due to dissociation, exception is ammonia

      1. Aqueous Solutions of Acids

        Arrhenius acids are molecular compounds with one or more ionizable hydrogens

        Water solutions are called aqueous acids

        Pure aqueous acids are electrolytes.

        3 + H 2 O ---> H 3 O 1+ + NO 3 1-

        HCl + H
        2 O ---> H 3 O 1+ + Cl 1-

        Figure 15-6 page 459

      2. Strength of Acids
        strong acid - definition

        examples: perchloric acid, nitric acid

        depends on polarity of bond between hydrogen and the anion to which is is bonded

        more polar and less bond energy means greater acid strength

        weak acid - definition

        examples: hydrocyanic acid

        HCN + H
        2 O = H 3 O 1+ + CN 1-

        where the equilibrium is far to the left i.e. many molecules, few ions

        table 15-3 page 460

        strong acids are assumed to ionize completely to produce at least one hydrogen (hydronium) ion

        in table 15-3 note that the strength does not depend on the number of hydrogens in the formula

        e.g. H
        3 PO 4 is a weak acid while HCl is a strong acid

        Organic Acids contain the carboxyl group -COOH

        They are generally weak acids.

        example: acetic acid

        3 COOH + H 2 O = H 3 O 1+ + CH 3 COO 1-

        where the equilibrium is far to the left i.e. many molecules, few ions

        only the hydrogen in the carboxyl group is ionizable

        figure 15-7 page 461
      3. Aqueous Solutions of Bases

        usual bases are metal cations and OH
        1- anions - ionic compounds, therefore, dissociation

        alkaline - definition

        one common base that is not ionic is ammonia, NH
        3, which undergoes ionization

        3 + H 2 O = NH 4 1+ + OH 1-

      4. Strength of Bases

        strength depends on the extent of ionization - how many hydroxides it creates in solution

        a strong base would be KOH

        strong bases are strong electrolytes

        table 15-4 page 461

        bases that are slightly soluble produce few hydroxide ions and are weak bases
        e.g. copper (II) hydroxide

        figure 15-8 page 462

        the higher the concentration of hydroxide ions in solution the stronger the base
        ammonia is highly soluble but a weak base because it produces few hydroxide ions in solution

        organic compounds with nitrogen are also weak bases

        e.g. aniline C
        6 H 5 NH 2 where it picks up a hydrogen ion from water to produce hydroxide ions

        Homework: 15.1
  2. Acid and Base Theories

    Arrhenius' theory required aqueous solutions

    Some substances behaved like acids or bases without water

    Other theories arose to account for these

    1. Bronsted-Lowry Acids and Bases

      Bronsted-Lowry acid - definition

      a hydrogen ion is a proton

      e.g. HCl + NH
      3 ---> NH 4 1+ + Cl 1-

      The hydrogen chloride donates a proton to the ammonia and so behaves like a Bronsted acid.

      The same happens with the reaction of hydrogen chloride and water.

      Water behaves like a Bronsted acid when it reacts with ammonia.

      Bronsted Lowry base - definition

      Bronsted-Lowry acid base reaction - definition

      e.g. reaction of hydrogen chloride and ammonia

      HCl + NH
      3 ---> NH 4 1+ + Cl 1-

      1. Monoprotic and Polyprotic Acids

        monoprotic acid - definition

        perchloric acid, HClO

        nitric acid, HNO

        hydrochloric acid, HCl

        polyprotic acid - definition

        sulfuric acid, H
        2 SO 4

        phosphoric acid, H
        3 PO 4

        Polyprotic acids lose their hydrogen one at a time, in stages

        diprotic acid - definition

        triprotic acid - definition

        Most polyprotic acids have the greatest concentration of ions in the first ionization and each subsequent ionization in the process produces fewer ions

    2. Lewis Acids and Bases

      Both previous theories assume the presence of hydrogen ions.

      Lewis based his theory on bonding and structure, whether the substance contains hydrogen ions or not.

      This is the same person whose name is associated with Lews Dot Structures.

      Lewis Acid - definition

      Broadest of the definitions.

      A hydrogen ion can be a Lewis acid by accepting an electron pair to form a covalent bond.

      e.g. page 467 silver ion

      Can include any atom with three valence electrons that can form three covalent bonds

      Table 15-5 page 468

      Lewis Base - definition

      An anion with an electron pair it can donate can be a Lewis base.
      page 468 fluoride ion

  3. Acid Base Reactions

    Use Bronsted-Lowry defintion to describe reactions in this section

    1. Conjugate Acids and Bases

      A substance that gives up a proton and subsequently accept a proton if there is a reverse reaction or something similar.

      Conjugate Base - definition

      page 469

      Conjugate acid-base pairs are the acid and its conjugate base and the base and its conjugate acid.

      1. Strength of Conjugate Acids and Bases

        The extent of the reaction between a Bronsted-Lowry acid and base depends on the relative stengths of the acids and bases involved. i.e. How far the forward reaction goes before equilibrium depends on the strength of the acid and base.

        page 470 HCl + water

        HCl gives up its proton readily -- strong acid -- so the chloride ion will not accept a proton readily; the stronger the acid the weaker its conjugate base; the strong the base, the weaker its conjugate acid.

        page 470 perchloric acid + water

        comparing the ability of perchloric acid v hydronium ion is ability to donate a proton; evidence of concentrations done by experimentation.

        page 470 acetic acid + water

        The stronger acid and base reaction will be the favored reaction i.e. you will have more of the weaker acid and base in solution than the stronger.

        Table 15-6 page 471

        Mixing a very strong acid with a very strong conjugate base could be dangerous.

    2. Amphoteric Compounds

      Amphoteric - definition

      page 472 sulfuric acid + water

      page 472 ammonia + water

      The strength of the substance it is reacting with determines if the amphoteric substance will act as either an acid or a base.

      1. -OH in a Molecule
        Molecular compounds containing an -OH group can be acidic or amphoteric.

        The hydroxyl group is -OH

        A compound with a hydroxyl group must be able to donate the hydrogen of that group to a water molecule to be an acid. The more polar the bond between the O--H the more likely this will happen. When the -OH is attached to a nonmetal from the upper right of the periodic table it has a polar bond that allow the hydrogen from the hydroxyl group to be donated to water.

        This includes all oxyacids such as sulfuric, phosphoric, etc.

        Figure 15-12 page 472 oxyacids of chlorine

        More oxygen atoms attached to the chlorine, the more polar the bond between the O-H will be and the more likely the compound will donate the hydrogen of the hydroxyl group.

        page 473 Compounds containing chromium and -OH group

        Figure 15-13 page 473

    3. Neutralization Reactions

      Acid + base ---> salt + water

      Acid properties usually cancel basic properties to yield neutral substance (salt) in water.

      sodium bicarbonate + tartaric acid in baking powder


      1. Strong Acid-Strong Base Neutralization

        HCl is a strong acid

        NaOH is a strong base

        HCl + H
        2 O ---> H 3 O 1+ + Cl 1-

        (aq) ---> Na + (aq) + OH 1- (aq)

        Mixing the two solutions produces an ionic equation that can be reduced to the reaction between the hydronium ion and the hydroxide ion to produce water.

        Neutralization - definition

        Salt - definition

      2. Acid Rain

        Nonmetal oxides that are the result of industrial processes can react with moisture in the air to produce acids. These acids can mix with rain/snow and produce acid rain.

        e.g. SO
        3(g) + H 2 O (l) ---> H 2 SO 4(aq)

        which when it comes in contact with marble gives the reaction

        3(s) + 2 H 3 O (1) + ---> Ca 2+ (aq) + CO 2(g) + 3 H 2 O (l)

        Figure 15-15 page 475

        Homework: 15.3

        end of notes
  4. Definitions

    Binary acid is an acid that contains only two different elements: hydrogen and one of the more electronegative elements.

    An oxyacid is an acid that is a compound of hydrogen, oxygen, and a thir element, usually a nonmetal.

    An Arrhenius acid is a chemical compund that increases the concentration of hydrogen ions, in aqueous solution.

    An Arrhenius base is a susbtance that increases the concentration of hydroxide ions in aqueous solution.

    A strong acid is one that ionizes completely in aqueous solution.

    A weak acid is an acid that is a weak electrolyte.

    Alkaline is used to describe a solution of a base that completely dissociates in water to yield aqueous hydroxide ions.

    A Bronsted-Lowry acid is a molecule or ion that is a proton donor.

    A Bronsted-Lowry base is a molecule or ion that is a proton acceptor.

    In a Bronsted-Lowry acid base reaction protons are transferred from one reactant (the acid) to another (the base).

    A monoprotic acid is an acid that can donate only one proton (hydrogen ion) permolecule.

    A polyprotic acid is an acid that can donate more than one proton per molecule.

    A diprotic acid is an acid that can donate two protons per molecule.

    A triprotic acid is an acid that can donate three protons per molecule.

    A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond.

    A Lewis base is an atom, ion, or molecule that donates an electron pair to form a covalent bond.

    A Lewis acid base reaction is the formation of one or more covalent bonds between an electron pair donor and an electron pair acceptor.

    A conjugate base is the species that remains after a Bronted-Lowry acid has given up a proton. back

    A conjugate acid is the species that is formed when a Bronsted-Lowry base gains a proton.

    Amphoteric describes any species that can react as either an acid or a base.

    Neutralization is the reaction of hydronium ions and hydroxide ions to form water molecules.

    A salt is an ionic compound composed of a cation from a base and an anion from an acid.
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