Chapter 6
Acids and
Bases
Stomach Acid & Heartburn
• the cells that line your stomach produce
hydrochloric acid
 to kill unwanted bacteria
 to help break down food
 to activate enzymes that break down food
• if the stomach acid backs up into your esophagus, it
irritates those tissues, resulting in heartburn
 acid reflux
 GERD = gastroesophageal reflux disease = chronic
leaking of stomach acid into the esophagus
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Curing Heartburn
• mild cases of heartburn can be cured by
neutralizing the acid in the esophagus
swallowing saliva which contains bicarbonate ion
taking antacids that contain hydroxide ions and/or
carbonate ions
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Properties of Acids
• sour taste
• react with “active” metals
 i.e., Al, Zn, Fe, but not Cu, Ag, or Au
2 Al + 6 HCl AlCl3 + 3 H2
 corrosive
• react with carbonates, producing CO2
 marble, baking soda, chalk, limestone
CaCO3 + 2 HCl CaCl2 + CO2 + H2O
• change color of vegetable dyes
 blue litmus turns red
• react with bases to form ionic salts
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Common Acids
Chemical Name
Formula
Uses
Strength
Nitric Acid
HNO3
explosive, fertilizer, dye, glue
Strong
explosive, fertilizer, dye, glue,
batteries
metal cleaning, food prep, ore
refining, stomach acid
fertilizer, plastics & rubber,
food preservation
plastics & rubber, food
preservation, Vinegar
Sulfuric Acid
H2SO4
Strong
Hydrochloric Acid
HCl
Phosphoric Acid
H3PO4
Acetic Acid
HC2H3O2
Hydrofluoric Acid
HF
metal cleaning, glass etching
Weak
Carbonic Acid
H2CO3
soda water
Weak
Boric Acid
H3BO3
eye wash
Weak
Strong
Moderate
Weak
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Structures of Acids
• binary acids have acid hydrogens attached to
a nonmetal atom
HCl, HF
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Structure of Acids
• oxy acids have acid hydrogens attached to
an oxygen atom
H2SO4, HNO3
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Structure of Acids
• carboxylic acids have
COOH group
 HC2H3O2, H3C6H5O7
• only the first H in the
formula is acidic
 the H is on the COOH
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Properties of Bases
• also known as alkalis
• taste bitter
 alkaloids = plant product that is alkaline
 often poisonous
• solutions feel slippery
• change color of vegetable dyes
 different color than acid
 red litmus turns blue
• react with acids to form ionic salts
 neutralization
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Common Bases
Chemical
Name
sodium
hydroxide
potassium
hydroxide
calcium
hydroxide
sodium
bicarbonate
magnesium
hydroxide
ammonium
hydroxide
Formula
NaOH
Common
Name
lye,
caustic soda
Uses
soap, plastic,
petrol refining
soap, cotton,
electroplating
Strength
Strong
KOH
caustic potash
Strong
Ca(OH)2
slaked lime
cement
Strong
NaHCO3
baking soda
cooking, antacid
Weak
Mg(OH)2
milk of
magnesia
antacid
Weak
NH4OH,
{NH3(aq)}
ammonia
water
detergent,
fertilizer,
explosives, fibers
Weak
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Structure of Bases
• most ionic bases contain OH ions
NaOH, Ca(OH)2
• some contain CO32- ions
CaCO3 NaHCO3
• molecular bases contain structures
that react with H+
mostly amine groups
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Indicators
• chemicals which change color depending on
the acidity/basicity
• many vegetable dyes are indicators
anthocyanins
• litmus
from Spanish moss
red in acid, blue in base
• phenolphthalein
found in laxatives
red in base, colorless in acid
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Arrhenius Theory
• bases dissociate in water to produce OH- ions and
cations
ionic substances dissociate in water
NaOH(aq) → Na+(aq) + OH–(aq)
• acids ionize in water to produce H+ ions and anions
because molecular acids are not made of ions, they cannot
dissociate
they must be pulled apart, or ionized, by the water
HCl(aq) → H+(aq) + Cl–(aq)
in formula, ionizable H written in front
HC2H3O2(aq) → H+(aq) + C2H3O2–(aq)
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Arrhenius Theory
HCl ionizes in water,
producing H+ and Cl– ions
NaOH dissociates in water,
producing Na+ and OH– ions
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Hydronium Ion
• the H+ ions produced by the acid are so reactive they
cannot exist in water
 H+ ions are protons!!
• instead, they react with a water molecule(s) to produce
complex ions, mainly hydronium ion, H3O+
H+ + H2O  H3O+
 there are also minor amounts of H+ with multiple water
molecules, H(H2O)n+
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Arrhenius Acid-Base Reactions
• the H+ from the acid combines with the OHfrom the base to make a molecule of H2O
it is often helpful to think of H2O as H-OH
• the cation from the base combines with the
anion from the acid to make a salt
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
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Problems with Arrhenius Theory
• does not explain why molecular substances, like
•
•
•
NH3, dissolve in water to form basic solutions –
even though they do not contain OH– ions
does not explain how some ionic compounds, like
Na2CO3 or Na2O, dissolve in water to form basic
solutions – even though they do not contain OH–
ions
does not explain why molecular substances, like
CO2, dissolve in water to form acidic solutions –
even though they do not contain H+ ions
does not explain acid-base reactions that take place
outside aqueous solution
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Brønsted-Lowry Theory
• in a Brønsted-Lowry Acid-Base reaction, an
H+ is transferred
 does not have to take place in aqueous solution
 broader definition than Arrhenius
• acid is H donor, base is H acceptor
 base structure must contain an atom with an
unshared pair of electrons
• in an acid-base reaction, the acid molecule
gives an H+ to the base molecule
H–A + :B  :A– + H–B+
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Brønsted-Lowry Acids
• Brønsted-Lowry acids are H+ donors
any material that has H can potentially be a
Brønsted-Lowry acid
because of the molecular structure, often one H in
the molecule is easier to transfer than others
• HCl(aq) is acidic because HCl transfers an H+ to
H2O, forming H3O+ ions
water acts as base, accepting H+
HCl(aq) + H2O(l) → Cl–(aq) + H3O+(aq)
acid
base
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Brønsted-Lowry Bases
• Brønsted-Lowry bases are H+ acceptors
any material that has atoms with lone pairs can
potentially be a Brønsted-Lowry base
because of the molecular structure, often one atom
in the molecule is more willing to accept H+ transfer
than others
• NH3(aq) is basic because NH3 accepts an H+
from H2O, forming OH–(aq)
water acts as acid, donating H+
NH3(aq) + H2O(l)  NH4+(aq) + OH–(aq)
base
acid
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