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Acids and Bases pH and Titrations

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Chances are, almost all of the foods that you associate with ... Grapefruit citric acid. Apples malic acid. Sour milk lactic acid. Vinegar acetic acid ... – PowerPoint PPT presentation

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Title: Acids and Bases pH and Titrations


1
Acids and BasespH and Titrations
  • 16-2

2
How many foods can you think of that are sour?
  • Chances are, almost all of the foods that you
    associate with being sour, owe their sour taste
    to an acid
  • Lemons citric acid
  • Grapefruit citric acid
  • Apples malic acid
  • Sour milk lactic acid
  • Vinegar acetic acid
  • Grapes tartaric acid

3
How many bases can you think of?
  • Ammonia
  • Sodium hydroxide lye drain cleaner
  • Milk of magnesia Mg(OH)2 antacid
  • Aluminum hydroxide antacid
  • Baking soda sodium hydrogen carbonate

4
Properties of Acids
  • Aqueous solutions of acids have a sour taste.
  • Acids change the color of acid-base indicators.
  • Some acids react with active metals to release
    hydrogen gas.
  • Acids react with bases to produce salts and
    water.
  • Some acids conduct electric current.

5
Bases
  • Aqueous solutions of bases taste bitter.
  • Bases change the color of acid-base indicators.
  • Dilute aqueous solutions of bases feel slippery.
  • Bases react with acids to produce salts and
    water.
  • Bases conduct electric current.

6
Strength of acids
  • A strong acid is one that ionizes completely in
    aqueous solutions.
  • The strength of an acid depends on the polarity
    of the bond between hydrogen and the element to
    which it is bonded and the ease with which that
    bond can be broken.
  • Acid strength increases with increasing polarity
    and decreasing bond energy.
  • Acids that are weak electrolytes are weak acids.

7
Strength of Bases
  • The strength of a base depends on the extent to
    which the base dissociates.
  • Strong bases are strong electrolytes.
  • Strong bases calcium hydroxide, barium
    hydroxide, sodium hydroxide, etc
  • Weak bases ammonia, aniline
  • Table 15-4 page 461

8
Indicators and pH meters
  • Acid-Base indicators are compounds whose color is
    sensitive to pH.
  • The color of an indicator changes as the pH of a
    solution changes.
  • Indicators come in many colors.
  • The pH range over which an indicator changes
    color also varies. This pH range is also called
    the transition interval.

9
Indicators and pH meters cont
  • A universal indicator is made by mixing several
    different indicators.
  • If an exact value for the pH of a solution is
    needed, a pH meter should be used.
  • A pH meter determines the pH of a solution be
    measuring the voltage between the two electrodes
    that are placed in the solution.

10
Titration
  • A neutralization reaction occurs between an acid
    and a base.
  • Because acids and bases react, the progressive
    addition of an acid to a base or vice versa can
    be used to compare the concentrations of the acid
    and the base.

11
Titrations cont
  • Titration is the controlled addition and
    measurement of the amount of a solution of known
    concentration required to react completely with a
    measure amount of a solution of unknown
    concentration
  • Titration provides a sensitive means of
    determining the chemically equivalent volumes of
    acidic and basic solutions.

12
Equivalence Point (E.P.)
  • The point at which the two solutions used in a
    titrations are present in chemically equivalent
    amounts is the equivalence point (e.p.).
  • Indicators and pH meters cane be used to
    determine the e.p.
  • A pH meter will show a large voltage change
    occurring at the e.p.
  • An indicator changes color over a range that
    includes the pH of the e.p.

13
End point
  • The point in a titration at which an indicator
    changes color is called the end point.

14
Which indicator should you use?
  • Indicators that undergo transition at about pH 7
    are used to determine the equivalence point of
    strong acid/ strong base titrations because the
    neutralization of strong acids with strong bases
    produces a salt solution with a pH of
    approximately 7.

15
Which indicator should you use?
  • Indicators that change color at pH lower that 7
    are useful in determining the equivalence point
    of strong acid/ weak base titrations. The
    equivalence point of this titration is acidic
    because the salt formed is a weak acid. Thus the
    salt solution has a pH lower than 7.

16
Which indicator should you use?
  • Indicators that change color at pH higher than 7
    are useful in determining the equivalence point
    of weak acid/ strong base titrations. These
    reactions produce salt solutions whose pH is
    greater than 7. This occurs because the salt
    solution formed is a weak base.

17
Which indicator should you use?
  • To determine the equivalence point for a weak
    acid/ weak base, we use no indicator. The pH of
    the equivalence point of weak acids and weak
    bases may be almost any value, depending on the
    relative strengths of the reactants. The color
    transition of an indicator helps very little in
    determining whether reactions between weak acids
    and bases are complete.

18
Molarity and titration
  • To calculate the molarity of a substance using
    titration
  • Start with the balanced equation and determine
    the chemically equivalent amounts of the acid and
    base.
  • Determine the moles of acid or base from the
    known solution used in the titration.

19
Molarity and titration
  • Determine the moles of solute of the unknown
    solution used during the titration.
  • Determine the molarity of the unknown solution.
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