ACIDS AND BASES

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ACIDS AND BASES

• http//www.visionlearning.com/library/module_viewe
  r.php?mid58

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ACIDS

• The term acid comes from the Latin terms acere,
  which means "sour and acidus, which means
  sharp.
• Acids taste sour, are corrosive to metals, change
  litmus (a dye extracted from lichens) red, and
  become less acidic when mixed with bases.
• Acids are compounds that contain hydrogen and can
  dissolve in water to release hydrogen ions into
  solution.
• HCl H20? H(aq)  Cl-(aq)

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BASES

• Bases feel slippery, change litmus blue, and
  become less basic when mixed with acids.
• Another word for base is ALKALI. Where have we
  heard that before???
• Bases are substances that dissolve in water to
  release hydroxide ions (OH-) into solution.
• NaOH H20?  Na(aq)  OH-(aq)

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NEUTRALIZATION

• As you can see from the equations, acids release
  H into solution and bases release OH-. If we
  were to mix an acid and base together, the H ion
  would combine with the OH- ion to make the
  molecule H2O, or plain water (neutral substance)
• H(aq)  OH-(aq)  ? H2O

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• The neutralization reaction of an acid with a
  base will always produce water and a salt, as
  shown below
• Acid Base ? Water Salt
• HCl   NaOH ? H2O    NaCl
• HBr    KOH  ? H2O   KBr

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PREDICT ACID OR BASE?

• Lemons/limes

ACID
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• Pickles

ACID
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• Baking soda (NaHCO3)

BASE
10

• Hand soap

BASE
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• Ammonia (NH3)

BASE
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• Tums

BASE
13

• Coffee

ACID
14

• Apple juice

ACID
15

• Drain cleaner

BASE
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• Tomatoes

ACID
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• Glass cleaner

BASE
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• Normal rain water

SLIGHTLY ACIDIC
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• Water (H2O)

NEUTRAL
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How do we measure how acidic or basic something
is?

• Both acids and bases are related to the
  concentration of hydrogen ions present. 
• Acids increase the concentration of hydrogen
  ions, while bases decrease the concentration of
  hydrogen ions (by accepting them to form H2O). 
• The acidity or basicity of something therefore
  can be measured by its hydrogen ion
  concentration.
• This is done with the pH scale.

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The pH scale is described by the formula

• pH -log H
• Note concentration is commonly abbreviated by
  using square brackets, thus, H hydrogen ion
  concentration.  When measuring pH, H is in
  units of moles of H per liter of solution.

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What does THAT mean?

• For example, a solution with
• H 1 x 10-7 moles/liter has a pH equal to 7
  (a simpler way to think about pH is that it
  equals the exponent on the H concentration,
  ignoring the minus sign).
• H 1 x 10-7 plugged into the equation is
• -log 1 x 10-7 -log10 -7 -(-7) 7

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Measuring pH

• The pH scale ranges from 0 to 14.
• Substances with a pH between 0 and less than 7
  are acids (pH and H are inversely related -
  lower pH means higher H).
• Substances with a pH greater than 7 and up to 14
  are bases (higher pH means lower H). Right in
  the middle, at pH 7, are neutral substances,
  for example, pure water.

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The pH scale
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What is the pH? Is it acid/base/neutral?

• -log 1 x 10-9
• -log 1 x 10-7
• H 1 x 10-3
• H 1 x 10-13

base
pH 9
neutral
pH 7
pH 3
acid
base
pH 13