Acids and Bases
• Acids
Unit 13 – Acids, Bases, and Salts
• What are some common properties of acids and bases?
• How is the concept of pH used to measure the strength of
acidic and basic solutions?
• What are acids and bases used for?
Acids and Bases
• Bases
– Sting to the touch
– Taste Sour
– React with metals
– Turn blue litmus red
– Ex: H2SO4, HC2H3O2
(vinegar)
Acids and Bases
• Strong Acids/Bases
– Slippery to the touch
– Taste bitter
– Unreactive with metals
– Turn red litmus blue
– Ex: Mg(OH)2 , NaHCO3
(Baking Soda)
Acids and Bases
• Arrhenius
• Acid
– Releases hydrogen
ions (H+) in water
– Creates H3O+
(hydronium)
• Base
– Releases hydroxide
ions (OH-) in water
– Completely dissociate
– Ex: HCl, NaOH
• Weak Acids/Bases
– Only slightly dissociate
– Citric acid, Ammonia
(NH3)
Acids and Bases
• Brønsted - Lowry
• Acid
– Proton donor (H+)
– Must have hydrogen
in formula
• Base
– Proton acceptor (H+)
• Water can be an acid or
a base
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Acids and Bases
• The Brønsted – Lowry theory leads to some
important terms:
• Conjugate acid
– Product formed when base accepts a proton (H+)
• Conjugate base
– Product formed when acid donates a proton (H+)
• Amphoteric
– Able to exist as an acid or a base
Acid-Base Reactions
• Neutralization
– Acid and Base produce a water and a Salt
• Anion from acid and cation from a base
• Neutral
• Titration
– Neutralization reaction
– Adding a solution of known concentration to
determine the concentration of another solution
Acid-Base Reactions
Acidity/Basicity
• Ion Concentrations
• Indicator
– Substance that changes color in certain pH ranges
– Used to show equivalency in titrations (End Point)
– Examples:
• Phenolphthalein – clear acid, pink base
• Universal indicator – red acid, green neutral, blue
base
• Phenol red – yellow acid, red base
• Bromthymol blue – yellow acid, blue base
– Based on H2O
Kw = [H+][OH-]
– Kw = 1.0 x 10-14
• Ion-product constant of water
– [H+]
• Concentration of hydrogen ion (M)
– [OH-]
• Concentration of hydroxide ion (M)
Acidity/Basicity
• For an aqueous solution:
– When [H+] and [OH-] are even, the solution is:
• Neutral
– If [H+] is greater than [OH-] the solution is:
• Acidic
– If [OH-] is greater than [H+] the solution is:
• Basic (aka Alkaline)
Acidity/Basicity
• pH
– Measure of hydrogen ion [H+] concentration
– Lower pH = more acidic
– pH calculations are based on logs
• Power of ten for a number
• Ex : log(103) = 3, log(10-3) = -3
pH = – log [H+]
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