Aim AB 1a
What are the
properties of
Acids and
Bases?
Question: What is an electrolyte?
• Electrolytes – think Gatorade!
– As substances dissolve, ionic substances
release free ions
– Ions carry a charge
– Electrolytes can therefore carry electricity
– How do we test for electrolyte solutions?
Properties of Acids
• Examples to the right; what do
they have in common?
• They are all electrolytes
– conduct electricity when aqueous
• They taste sour – think lemons
• They are corrosive - break down materials
• React with active metals to release hydrogen gas
Ex: HCl(aq) + Mg(s)  MgCl(aq) + H2(g)
• Neutralize bases to form a salt and water in a
double replacement reaction
Ex: HCl(aq) + NaOH(s)  NaCl(aq) + HOH(l)
ACID
base
salt
water
Properties of Acids
• Cause color changes in indicators
(A chemical that reacts with an acid
or base and shows a color change)
– blue litmus paper
• changes to red
• (aciD = reD)
– phenolphthalein solution
• changes to clear
• pH scale – indicates level of acidity
or basicity of a solution
• pH of 1 – 6 indicates an acid
• pH of 7 is neutral
• pH of 8 – 14 indicates a base
Commonly used Acids Regents Chemistry
Table K Common Acids
• Monoprotic acid
– only one H+ released
– HCl, HNO3
• Diprotic acid
– Two H+ ions released
– H2CO3, H2SO4
• Triprotic acid
– Three H+ ions released
– H3PO4
Properties of Bases
• Examples to the right; what
do they have in common?
• They are all electrolytes
– conduct electricity when
aqueous
• They taste bitter – what does
that tell you about coffee, especially Starbucks?
• They are caustic – break down skin tissue
• Feel slippery to the touch – many soaps have this
characteristic
• Neutralize bases to form a salt and water in a double
replacement reaction
Ex: HCl(aq) + NaOH(s)  NaCl(aq) + HOH(l)
acid
BASE
salt
water
Properties of Bases
• Cause color changes in indicators
– red litmus paper
• changes to blue color
• (Blue = Base)
– Phenolphthalein solution
• changes to pink color
• pH scale – indicates level of
acidity or basicity of a solution
• pH of 1 – 6 indicates an acid
• pH of 7 is neutral
• pH of 8 – 14 indicates a base
Commonly used Bases Regents Chemistry
• Monohydroxy base - only one OH- released
– NaOH, KOH
• Dihydroxy base - two OH- ions released
– Ca(OH)2
• Ammonia – special case (more later)
Table K Common Bases
Real World
Acid/Base
Applications
• Acid Rain
– Forms from the
reactions of sulfur and nitrogen oxides reacting
with moisture in the air
– Increases the acidity of rainwater
– Falls into lakes and ponds
– Eats at metals in the lakebeds, ionizing them
and polluting the lakes and ponds
– Remediation – add lime (base material) to
neutralize the acid in the lake – expensive!
Uses of Acids
• CH3COOH - Acetic acid
– Vinegar in very dilute solution form (3% solution)
• HCl – hydrochloric acid
– pH control for swimming pools
– Cleaning material for tiles "muriatic acid“
• H2SO4 - sulfuric acid
– battery acid in your car
• HNO3 – nitric acid
– Reaction with ammonia to make fertilizers
– Reaction with glycerol and toluene to make TNT
• H3PO4 – phosphoric acid
– can be used to remove rust
Uses of Bases
• NaOH – sodium hydroxide
– one of the most used bases in industrial
processes, also called "lye" and is in some
soaps
– can be used as a drain cleaner
• NH3 – ammonia
– most common use as a home cleaner
• Used in the production of fertilizers
• NaHCO3 - sodium bicarbonate
– is present in most baking powder
• CaO – calcium oxide – when mixed with water,
creates Ca(OH)2 – calcium hydroxide
– used in plaster, called quicklime
Aim AB 2b
How do we explain the difference between
Acids and Bases on a molecular level?
Acid/Base Theories
• There are two theories that describe the difference
between acids and bases on the atomic level
• Arrhenius Theory compares acids and bases in
terms of two ions
– Arrhenius Acids – release hydrogen ions (H+)
when dissolved in solution
– Arrhenius Bases – release hydroxide ions (OH-)
when dissolved in solution
• Bronsted Lowry Theory (also known as the “other”
theory in Regents Chemistry) describes acids and
bases in terms of being able to donate or accept a
proton
Arrhenius Theory of Acids and Bases
• An Arrhenius Acid is:
– A substance that ionizes in water to
produce hydrogen ions (H+)
– Since H+ ions can’t exist alone in solution,
they combine with water to form
hydronium ions (H3O+)
HCl(g)  H+(aq) + Cl–(aq)
or
H2O(l) + HCl(g)  H3O+(aq) + Cl–(aq)
Arrhenius Theory of Acids and Bases
• An Arrhenius Base is:
– A substance that ionizes in water to
produce hydroxide ions (OH-)
NaOH(s)  Na+(aq) + OH–(aq)
• Note!!! Carbon compounds with hydroxide
ions (OH-) are NOT bases – they are
alcohols and are neither acid nor base!
• Examples:
• CH4OH (methanol) and C2H5OH (ethanol)
Other Theories:
• Bronsted-Lowry Theory of Acids
– any substance that can donate or give up a
proton (proton = H+ ion)
– Example: NH4+ (ammonium) can donate a proton
H20(l) + NH4+  NH3(aq) + H2O +(aq)
• Bronsted Lowry Theory of Bases
– any substance that can accept a proton
– Usually have a free, unshared pair of electrons
that the proton (H+) can attach to
– NH3 (ammonia) has an unshared pair of electrons
H2O(l) + NH3  NH4+ (aq) + OH -(aq)
Other Theories
• Bronsted-Lowry Theory describes how
some molecules can act as either an acid
or a base
• These are Amphiprotic or Amphoteric
substances
– They have hydrogen ions to give up like an
acid
– They have unshared electrons to absorb
hydrogen ions like a base
– Depending on what molecules they hook
up with, they can act as either an acid or
base
Other Theories
• Examples of Amphiprotic or Amphoteric
substances
– Water can donate or accept a H+ ion
H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
Base Acid
Acid
Base
– Ammonia can donate a H+ ion like an acid
NH3(g) + H2O(g)  NH2-(aq) + H3O+(aq)
Acid
Base
Base
Acid
– or accept a H+ ion like a base
NH3(g) + H2O(g)  NH4+(aq) + OH-(aq)
Base
Acid
Acid
Base
Aim AB 3c
- Why does
lemon juice
sting when I
get it in my
eye?
How does acid cause ulcers and heartburn?
• A property of acids is
their corrosiveness
• This includes your
stomach lining when
you are stressed or eat
overly spicey food
• Why do acids have this
characteristic?
• Its all in their pH
pH – how acidic or
basic a substance is
•
•
•
•
Symbol for concentration [ ]
[X] = Concentration of X
REMEMBER = Water is polar
Slightly (+) hydrogens of one water molecule
Are attracted to (-) oxygens of another
Because of this, water ionizes (forms (+)
and (-) ions) to a very small extent:
H2O + H2O  H3O+ +
Acid part
of water
OH–
Base part
of water
Symbol for concentration [ ]
pH – how acidic or
[X] = Concentration of X
basic a substance is
• For every water molecule that becomes an
acid ion, one becomes a base ion
• This evens out
– for every H3O+ ion there is an OH– ion
– When they combine, they make 2 water
molecules
• The concentration of the ions in pure water is
measured in moles/liter (molarity)
[H3O+] = 10–7 M or 0.0000001 M
[OH–] = 10–7 M or 0.0000001 M
pH – how acidic or
Symbol for concentration [ ]
basic a substance is
[X] = Concentration of X
• The acid and base concentrations, when
multiplied together, equals a constant value:
[H3O+] = 10–7 M
[OH–] = 10–7 M
[H3O+] x [OH–] = 10–14 M
[Acid] x [Base] = constant
• In any solution, including acids or bases
• The concentration constant
of [H3O+] x [OH–] is equal to 10-14 M
pH – how acidic or
basic a substance is
Symbol for concentration [ ]
[X] = Concentration of X
• In acids, there are more H3O+ ions (acid ions)
than OH– ions (base ions)
• Example: HCl is added to water. The H+
concentration rises to 10-4 M. What would the
OH- concentration be?
[H3O+ ] x [OH-] = 10-14 M
10-4 x [OH-] = 10-14 M
[OH-] = 10-10 M
• Note – the bigger the negative exponent, the
smaller the amount you are dealing with
– [H3O+ ] = 10-4 M
= 0.0001 M
– [OH-] = 10-10 M
= 0.0000000001 M
pH – how acidic or
basic a substance is
Symbol for concentration [ ]
[X] = Concentration of X
• In bases, there are more OH– ions (base ions) than
H3O+ ions (acid ions)
• Example: NaOH is added to water. The OHconcentration rises to 10-3 M. What would the
H3O+ concentration be?
[H3O+ ] x [OH-] = 10-14 M
[H3O+ ] x 10-3 = 10-14 M
[H3O+ ] = 10-11 M
So where does pH come from???
• We said in the previous slides the following:
• For water,
– The [H3O+ ] was 10-7 and the [OH- ] was 10-7
– Its pH is 7, or NEUTRAL
• For an acid,
– The [H3O+ ] was 10-4 and the [OH- ] was 10-10
– Its pH is 4, or ACIDIC
• For a base,
– The [H3O+ ] was 10-11 and the [OH- ] was 10-3
– Its pH is 11, or Basic
• So, to calculate pH, we look at the exponent
of the acid part to get the pH
So, to calculate pH, what do we look at?
• Example 1: a solution has a hydronium [H3O+ ]
concentration 10-4 M.
– What is the hydroxide [OH- ] concentration?
• [H3O+ ] x [OH- ] = 10-14 (a constant)
• 10-4 M x [OH- ] = 10-14
• [OH- ] = 10-10
– What is the pH of the solution?
• Look at the exponent of the [H3O+ ]
• [H3O+ ] = 10-4 = pH of 4 , acidic
So, to calculate pH, what do we look at?
• Example 2: a floor cleaning solution has a
hydroxide [OH- ] concentration 10-6 M.
– What is the hydronium [H3O+ ] concentration?
• Remember:
–[H3O+ ] x [OH- ] = 10-14 (a constant)
–[H3O+ ] x 10-6 M x = 10-14
–[H3O+ ] = 10-8
– What is the pH of the solution?
• Look at the exponent of the [H3O+ ]
• [H3O+ ] = 10-8 = pH of 8 , basic
Aim AB 4d
Oh no! How do I
clean up the
Liquid Plumber
on my kitchen
floor safely?
A student spills a container
of acid on the floor. What
does the student need to
add to the acid to get rid of
it?
• Wipe it up?
• Water it down?
• What else could be done?
• More than anything else - the acid needs to
be neutralized
Neutralization is a special
DOUBLE REPLACEMENT reaction
• It reacts an acid with a base to form a salt
and water
• Acid + Base  Water
+ Salt
• General formula
• HA
+ BOH  HOH
+ BA
• Examples
• HCl + NaOH  H2O
+ NaCl
• H2SO4 + 2 NaOH 2 H2O
+ Na2SO4
Neutralization / double replacement - determine the
products of each of the following neutralization
reactions:
1. KOH + HBr  H2O + KBr
2. H2SO4 + Ca(OH)2  2 H2O + CaSO4
•
Spectator ions
– ions that stay dissolved in the water of a
solution, do not react
– the ions that make up the soluble salts
tend to be spectator ions
•
•
Acid Base Indicators
tell us how acid or
basic a substance is
See Table M for
examples of various
indicators
The pH range on the
chart represents the
point that a color
change will occur
– Values to the left represent more acidic pHs
– Values to the right represent more basic pHs
Acid Base Indicator Examples
1. A solution leaves thymol blue a blue color and
litmus paper changes to blue; is the solution basic
or acidic?
– Thymol is blue above the 8.0 – 9.6 range
– Litmus changes blue above the 5.5 – 8.2 range
– Both show the solution above 8
– Solution is most likely basic
2. A solution changes methyl orange and litmus red
and has no effect on phenolphthalein. Is it basic
or acidic?
– Methyl orange changes red below 3.2 – 4.4
– Litmus changes red below 5.5 - 8.2
– Both show the solution below 7
– Solution is most likely acidic
Aim AB 5e
– How strong is my vinegar?
Acid Base Titration
• A method for determining the concentration
or molarity of an unknown acid or base, based
on
– the molarity of a known acid or base
– The volume of acid used
– The volume of base used
• Uses the process of neutralization and the
concept of endpoint
– Endpoint: the point when the last of the acid
and base are completely neutralized
– Determined using an indicator to show the
final neutralization point
• To determine the
molarity of an
unknown acid
solution
1 - you choose a
good indicator
2 - you choose a
known base
molarity
3 - you add the
base to the acid
till it changes
color
4 – you calculate
Calculating the molarity of an acid using
the titration method and formula
• By using the titration technique and the
endpoint of the neutralization reaction
• We can find out three things
1 - the molarity of the known base ( Mb )
2 - The volume of the base used ( Vb)
3 - The volume of the acid sample (Va)
• We can now use the last of our calculations in
CRT T to calculate the
Ma x Va = Mb x Vb
Example 1 – a 2.00 M acid solution is used to
titrate an unknown base solution. If 40.00 mL of
acid are used and 20.0 mL of base are used,
what is the molarity of the base?
Remember: M is molarity or concentration
V is measured in mL or liters
Ma x Va = Mb x Vb
2.00 M x 40.0 mL = Mb x 20.0 mL
4.00 M = Mb
Example 2: Tropicana is having an issue with
the citric acid levels in its new Tropicana
Grapefruit Infused Fresh juice. A quality
control chemist determines that 22 mL of an
1.0 M NaOH solution is used to neutralize
4400 mL of acidic TGIF juice. What is the
molarity of the juice?
Ma x Va = Mb x Vb
Ma x 4400.0 mL = 1.00 M x 22.0 mL
0.005 M = Ma
What is the pH of the Tropicana?
.0050 M = 5.0 x 10-3 = pH of 3
Example 3: A student performs a titration with a
known base. She collects the data shown below. If
the base has a molarity of 0.120 M, what is the
molarity of the acid?
Acid Volume
Starting Burette Measure
Ending Burette Measure
42.4 mL
22.4 mL
Base Volume
18.4 mL
13.4 mL
How much acid
How much base
was used?
was used?
42.4 mL – 22.4 mL
18.4 mL – 13.4 mL
= 20.0 mL
= 5.0 mL
Ma x 20.0 mL = 0.120 M x 5.0 mL
Ma = 0.030 M
Acid / Base Strengths
• HCl and H2SO4 release different numbers
of H+ ions!
– In the neutralization of NaOH,
H2SO4 + 2NaOH  2H2O + Na2SO4
• NaOH and Ba(OH)2 also release different
numbers of OH- ions!
– In the neutralization of Ba(OH)2Note:
2HCl + Ba(OH)2  2H2O + BaCl2