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H O N O R S C H E M I S T RY – S E M E S T E R 2
Acids & Bases
Name Some Acids
Name some familiar acids. Where are they found?
Acetic acid (vinegar)
Hydrochloric acid (in your stomach, pools)
Citric acid (citrus fruits)
Ascorbic acid (Vitamin C)
Sulfuric acid (car batteries, acid rain)
Carbonic acid (carbonated sodas)
Acids give tart, sour, tangy taste (e.g., vinegar, lemon)
Acids
Are electrolytes
Example: HCl dissolving in water
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)
Forms hydronium (H3O+) when dissolved in H2O
H3O+ able to transfer charge quicker than other ions
React with metals above hydrogen in the activity series
Produce hydrogen gas (H2)
Example: HCl(aq) + Zn(s) → H2(g) + ZnCl2(aq)
Resistant to acids!
Acidity in Aqueous Solutions
Aqueous solutions with large number of H3O+ =
acidic
Acid Classification
Strong acids = dissociate completely in solvent
Example: HNO3 (nitric acid)
HNO3(l) + H2O(l) → H3O+(aq) + NO3
-(aq)
Weak acids = release only few H+ in aqueous
solution
Example: HOCl (hypochlorous acid)
HOCl(l) + H2O(l) ↔ H3O+(aq) + ClO-(aq)
Strong vs. Weak Acids
Bases
Are electrolytes
Form hydroxide (OH-) when
dissolved in H2O
Range from very soluble to
nearly insoluble
Form basic (alkaline) solutions
Examples: Baking soda, ammonia, lye, carbonates and
phosphates
Ammonia fertilizer
Alkaline Solutions
Are slippery to the touch
React with oils in our skin
convert oils to soap
used in cleaning agents
Base Classification
Strong base = dissociates completely in a solvent
Example: NaOH(s) → Na+(aq) + OH-(aq)
Weak base = releases few OH- in aqueous solutions
Example: NH3(aq) + H2O(l) ↔ NH4+(aq) + OH-(aq)
majority of NH3 remains un-ionized!
Arrhenius Classification
Swedish scientist, Svante Arrhenius
Acids, dissolved in water, increase concentration
of hydrogen ions (H+)
Bases, dissolved in water, increase concentration
of hydroxide ions (OH-)
© 2012 Pearson Education, Inc.
Brønsted-Lowry Classification
Johannes Brønsted (Danish), Thomas Lowry
(British) independently defined ‘acid’ in 1923
Brønsted Lowry
Brønsted-Lowry acid
= substance that donates a proton (hydrogen nucleus) to
another substance
Example: HCl + H2O → H3O+ + Cl-
Brønsted-Lowry Classification
Brønsted-Lowry base
= substance that accepts a proton (= hydrogen atom)
Example: NH3 + H2O → NH4+ + OH-
Brønsted-Lowry Classification
Conjugate Acids & Bases
Per Brønsted-Lowry:
Lose a proton = acid
Accept a proton = base
“conjugate” from Latin “conjugare” (to join together)
Acid / base reactions yield conjugate bases and acids
Conjugate acid = forms when base gains a proton
Conjugate base = forms when acid loses a proton
Conjugate Acids & Bases
Strong acid conjugate base is extremely weak
Weak acid conjugate base is weak base
Strong base conjugate acid is extremely weak
Conjugate Acid-Base Pairs
Amphoteric Species
Amphoteric = substance with properties of both
acid AND base
Self-ionization of water