ACIDS AND BASES
Properties of Acids
 Acids are proton (hydrogen ion, H+) donors
 Acids have a pH lower than 7
 Acids taste sour
 Acids effect indicators
 Blue litmus turns red
 Methyl orange turns red
 Acids react with active metals, producing H2
 Acids react with carbonates
 Acids neutralize bases
Acids are Proton
+
(H
ion) Donors
Strong acids are assumed to be 100% ionized in
solution (good H+ donors).
HCl
H2SO4
HNO3
Weak acids are usually less than 5% ionized in
solution (poor H+ donors).
H3PO4
HC2H3O2
Organic acids
Acids
Have a pH
less than
7
Acids Taste Sour
Organic acids are weak acids. Some are used as
flavoring agents in food.
 Citric acid in citrus fruit
 Malic acid in sour apples
 Lactic acid in sour milk and
sore muscles
 Butyric acid in rancid butter
Organic Acids
Organic acids all contain the “carboxyl” group,
sometimes several of them.
The carboxyl group is a poor proton donor, so
ALL organic acids are weak acids.
Acids
Effect
Indicators
Blue litmus paper
turns red in contact
with an acid.
Methyl orange turns
red with addition of
an acid
Acids React with Active Metals
Acids react with active metals to form salts and
hydrogen gas.
Mg + 2HCl  MgCl2 + H2(g)
Zn + 2HCl  ZnCl2 + H2(g)
Mg + H2SO4  MgSO4 + H2(g)
Acids React with Carbonates
2HC2H3O2 + Na2CO3
2 NaC2H3O2 + H2O + CO2
Effects of Acid Rain on Marble
(calcium carbonate)
George Washington:
BEFORE
George Washington:
AFTER
Acids Neutralize Bases
Neutralization reactions ALWAYS produce a salt and
water.
HCl + NaOH  NaCl + H2O
H2SO4 + 2NaOH  Na2SO4 + 2H2O
2HNO3 + Mg(OH)2  Mg(NO3)2 + 2H2O
Properties of Bases
 Bases are proton (hydrogen ion, H+) acceptors
 Bases have a pH greater than 7
 Bases taste bitter
 Bases effect indicators
 Red litmus turns blue
 Phenolphthalein turns purple
 Solutions of bases feel slippery
 Bases neutralize acids
Bases are Proton (H+ ion) Acceptors




Sodium hydroxide (lye), NaOH
Potassium hydroxide, KOH
Magnesium hydroxide, Mg(OH)2
Calcium hydroxide (lime), Ca(OH)2
OH- (hydroxide) in base combines with H+ in
acids to form water
H+ + OH-  H2O
Bases
have a
pH
greater
than 7
Bases Effect Indicators
Red litmus paper turns blue in
contact with a base.
Phenolphthalein
turns bright pink
in a base.
Bases Neutralize Acids
Milk of Magnesia contains
magnesium hydroxide, Mg(OH)2,
which neutralizes stomach acid,
HCl.
2 HCl + Mg(OH)2
MgCl2 + 2 H2O
• Each acid has a proton available (an
ionizable hydrogen) and another part,
called the conjugate base. (That word,
'conjugate' just means that it "goes with"
the other part.) When the acid ionizes, the
hydrogen ion is the acid and the rest of the
original acid is the conjugate base. Nitric
acid, HNO 3, dissociates (splits) into a
hydrogen ion and a nitrate ion.
• The hydrogen almost immediately joins
to a water molecule to make a
hydronium ion. The nitrate ion is the
conjugate base of the hydrogen ion. In
the second part of the reaction, water is
a base (because it can accept a proton)
and the hydronium ion is its conjugate
acid.
HNO3
ACID
+
H2O
BASE
→ (NO3)- + (H3O)+
CONJUGATE
BASE
CONJUGATE
ACID
PROPERTIES OF ACIDS
1. Acids release a hydrogen ion into
water (aqueous) solution. You will
usually see the formula for an acid with
the ionizable hydrogen at the
beginning, such as HCl, hydrochloric
acid, or H(C2H3O2), acetic acid.
2. Acids neutralize bases in a
neutralization reaction. An acid and a
base combine to make a salt and water.
A salt is any ionic compound that could
be made with the anion of an acid and
the cation of a base. The hydrogen ion of
the acid and the hydroxide ion of the
base unite to form water.
3. Acids corrode active metals. Even gold, the
least active metal, is attacked by an acid,
a mixture of acids called 'aqua regia,' or
'royal liquid.' When an acid reacts with a
metal, it produces a compound with the
cation of the metal and the anion of the
acid and hydrogen gas.
4. Acids turn blue litmus to red.
Litmus is the oldest known pH indicator. It is
red in acid and blue in base. The phrase,
'litmus test,' indicates that litmus has been
around a long time in the English language.
Litmus does not change color exactly at the
neutral point between acid and base, but
very close to it. Litmus is often impregnated
onto paper to make 'litmus paper.'
5.Acids taste sour. TASTING LAB ACIDS IS
NOT PERMITTED BY ANY STUDENT.
The word 'sauer' in German means acid
and is pronounced almost exactly the
same way as 'sour' in English.
(Sauerkraut is sour cabbage, cabbage
preserved in its own fermented lactic
acid).
• Stomach acid is hydrochloric acid.
Although tasting stomach acid is not
pleasant, it has the sour taste of acid.
Acetic acid is the acid ingredient in
vinegar. Citrus fruits such as lemons,
grapefruit, oranges, and limes have citric
acid in the juice. Sour milk, sour cream,
yogurt, and cottage cheese have lactic
acid from the fermentation of the sugar
lactose.
PROPERTIES OF BASES
1. Bases release a hydroxide ion into
water solution. (Or, in the Lowry Bronsted model, cause a hydroxide ion
to be released into water solution by
accepting a hydrogen ion in water.)
2. Bases neutralize acids in a neutralization
reaction. The word - reaction is: Acid plus
base makes water plus a salt.
Where 'Y' is the anion of acid 'HY,' and 'X' is
the cation of base 'XOH,' and 'XY' is the
salt in the product, the reaction is:
HY + XOH
HOH + XY
3. bases denature protein. This accounts
for the "slippery" feeling on hands when
exposed to base. Strong bases that dissolve
in water well, such as sodium or potassium
lye are very dangerous because a great
amount of the structural material of
human beings is made of protein. Serious
damage to flesh can be avoided by careful
use of strong bases.
4. Bases turn red litmus to blue.
• This is not to say that litmus is the
only acid - base indicator, but that it
is likely the oldest one.
5. Bases Taste Bitter. There are very few
food materials that are alkaline, but those
that are taste bitter. It is even more
important that care be taken in tasting
bases. Again, NO STUDENT PERMITS
TASTING OF LAB CHEMICALS. Tasting of
bases is more dangerous than tasting acids
due to the property of stronger bases to
denature protein.
End of lecture
Part I