Acids and Bases
Experimental Definitions
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Acids
Turn blue litmus red
taste sour
corrode metals
Provide H+ ions
Conducts electricity
Bases(alkalis)
Turn red litmus blue
taste bitter
slippery feel
Provide OH- ions
Conducts electricity
Various Definitions of Acids &
Bases
Arrhenius Definition
• Acids release hydrogen ions in water:
H2O
• HCl
H+ + Cl•Bases release hydroxide ions in water:
H2O
NaOH
Na+ + OH-
An example of a Arrhenius
Reaction
• HCl(aq) + NaOH(aq) ---->Na+ + Cl- + OH- + H+
----------> NaCl (aq) + H O(l)
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• This definition works for most simple examples, but
there are some bases that do not release OH-.
• Ammonia gas (NH3) is an example of a base that does
not follow Arrhenius’ rule.
• We need a new definition!!
Brønsted - Lowry
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Acids are PROTON DONORS
Bases are PROTON ACCEPTORS
When HCN Dissolves in water a reaction occurs:
HCN + H2O ----> H3O+ + CNHCN is a Bronsted Acid
Water is acting as a Bronsted Base.
• If a substance acts as a a proton donor and a
proton acceptor it is said to be amphoteric.
Conjugate acids and bases
Conjugate acid-base pairs differ
by a hydrogen ion.
• HCN + H2O ----> H3O+ + CN• Acid base conj. Acid
conj. base
Finding Conjugate Bases
* Remove a hydrogen ion from the acid.
• What would the conjugate bases be for the
following 3 acids?
• HI
I• NH4+ NH3
• HSO4- SO4 2-
Finding Conjugate Acids
* Add a hydrogen ion to the base.
• What are the conjugate acids for the
following bases?
• SO42HSO4• NH3
NH4+
• C2H3O2- HC2H3O2
Bronsted-Lowery’s limitations…
• It would seem that Bronsted-Lowery is right on
target, but there are some acids and bases out there
that do not fit under either of our two sets of
definitions.
• Here are two reactions:
– CaO(s) + SO2(g) ---> CaSO3(s)
– H2SO3(aq) + Ca(OH)2(aq) ----> CaSO3(aq) + H2O
• The second reaction is clearly a Bronsted-Lowery
acid base reaction. BOTH reactions produce
CaSO3 (a Base), so could the first reaction also be
a acid-base reaction????
• We need another definition!!!
Lewis
• Lewis acids are
electron pair acceptors
• Lewis Bases are
electron pair donors
NH3 is the donor (Lewis
base) and BCl3 is the
acceptor (Lewis acid)
Ex: NH3 + BCl3-----> H3NBCl3
Molarity
• Molarity (M):
- Measure of concentration
- Defined as moles of solute per Liters of solution.
- M = mol/L
• Ex: What is the molarity of a solution obtained by
dissolving 24.5g of H2SO4 in enough water to
make 1.50L of solution?
Molarity practice problems
• 2. How many grams of Ca(OH)2 are there in
800.mL of a 2.0M Ca(OH)2 solution?
0.167M
• 3. What molarity of HNO3 solution would be
needed if 35.0mL of acid were needed to
neutralize 10.0mL of a 0.15M Mg(OH)2 solution?
(Hint: write the balanced equation!)
0.086 M
• 4. What is the molarity of an Fe(OH)3 solution if
a 10.0mL sample was neutralized using 30.mL of
a 0.20M HCl Solution?
0.2 M
Naming Acids: Binary acids
• Binary acids: H + element
• Format:
– Hydro________ic acid
– HCl = hydrochloric acid
• Name the following Binary Acids:
– HBr
– H2S
– HF
– H3N
Naming Acids: Ternary Acids
• Ternary Acids = H + polyatomic anion.
• Format
– “ate”------>
“ic”
– “ite”------->
“ous”
• H2SO4:
– SO42- is “sulfate”
– turn “ate” into “ic”
– Sulfuric acid
Name the following Ternary
Acids
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H2CrO4
HNO3
HClO4
H3PO4
HNO2
HClO2
HClO
Neutralization
• An Acid/ base reaction is called a neutralization
reaction.
• Double Displacement Reaction
• Ex: NaOH + HCl --> NaCl +HOH
• base + acid --> a salt + water
Anhydrides
• Anhydrides means “without water.”
• Anhydrides can be:
metallic or nonmetallic oxides (metals or
nonmetals bonded to oxygen)
A few formulas
• Making an acid:
• P2O5 + H2O -----> H3PO4
• Making a Base:
• CaO + H2O -----> Ca(OH)2
Nonmetallic
oxides make
acids in water
Metallic oxides
make bases in
water.
Working with Anhydrides
• Ex: What is the anhydride of H3PO4?
• Step1: Write out all the atoms. If there
is an ODD number of hydrogens, write it
out TWICE.
– HHHPOOOO
– HHHPOOOO
Anhydrides Cont.
• Step2: Cross off “H2O”s until all
hydrogens are gone.
– HHHPOOOO
– HHHPOOOO
Step 3: The group of atoms leftover is the
anhydride.
P2O5
Anhydrides of Bases
• Ex: Determine the anhydride for Ca(OH)2.
• CaOOHH
CaO
Anhydride Practice
• Al(OH)3
Al2O3
• HNO3
N2O5
• Mg(OH)2
MgO
• H2CO3
CO2
Hydrolysis
• Acid + Base ----> Salt + Water
• The salt can be neutral, acidic or basic!
• This is determined by the strength of the
acid and base you started with.
Solution Formed From Salt
Type of acid
Type of base
Solution
Strong
Strong
Neutral
Strong
Weak
Acidic
Weak
Strong
Basic
Weak
Weak
Neutral, basic,
or acidic
How do you tell if an acid is
strong?
• TEST #1: If the acid contains Oxygen
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Subtract # hydrogens atoms from # oxygens atoms.
If the difference is < 2 acid is WEAK.
If the difference is >2 acid is STRONG.
Ex: H2SO4 4 -2 = 2--> strong acid
H3PO4 4 - 3 = 1 --> weak acid
• TEST #2: If the acid does not contain oxygen.
—There are only 3 strong acids in this category.
— HBr, HI, HCl
How do you tell if a Base is
Strong?
• Bases: Metal ion + hydroxide ion.
Metal comes from IA family or
Ca, Ba, and Sr from family IIA.
Hydrolysis Example 1
• Is the salt NaCl acidic basic or neutral when
dissolved in water?
• First figure out which acids and bases the
salt came from
– __acid___ +_base__ ----> NaCl + HOH
HCL + NaOH ------> NaCl + HOH
Strong strong
neutral
Hydrolysis- more Practice
• Are each of the following salts acidic basic
or neutral?
• MgCO3
• Al(NO3)3
• CaSO4