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Acids and Bases!

A general overview
by

Nancy Cope

on 26 April 2016

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Transcript of Acids and Bases!

ACIDS AND BASES
Types of acids and bases
Three "schools of thought"
Bronsted Lowry
Lewis
Arrehenius
Bronsted-Lowry
Lewis
Arrhenius
Strength of Acids and Bases
Strong Acids
Strong Bases
Strength of an
acid
or
base
is dependent on how much the molecule dissociates. Molecules that dissociate complete are strong
acids
(or
bases
) because they produce
hydrogen ions
(or
hydroxide ions
) easily
pH
A measure of acid strength
pH < 7 is acidic
pH > 7 is basic
pH = 7 is neutral
a strong acid has a low pH
pH can be measured using
pH paper
pH meter
indicator
Litmus paper
can be used to indicate
if a substance is an acid or a base.
Acid makes
blue
litmus paper turn
red.
Base makes
red
litmus paper turn
blue.
pH Paper
turns different colors based on the pH of the solution
pH meters
have a probe that is submerged into a solution and the pH is then displayed on a digital screen
sour tasting
reacts vigorously with metals
good conductor of electricity
bitter tasting
slippery to touch
good conductor of electricity

have a strong affinity for H+ in water to form hydroxide ions.
Ionize completely in water.
Strong electrolyte
Weak base
does not have a strong affinity for H+.
Incomplete ionization.
Poor electrolytes.

readily transfer their H+ to water to form hydronium ions.
Ionize completely (dissociate completely).
Strong electrolytes
an electrolyte is a substance when dissolved in water is a good conductor of electricity.
Indicators
are dyes that change color in solution based on the pH of the solution. Different indicators change color at a different range of pH.
Weak acids
do not readily transfer their H+ to water.
Incomplete ionization.
Poor electrolytes
Most Bronsted Lowry Acids are Lewis Acids and Bronsted Lowry Bases are Lewis Bases
Properties of Acids
Properties of Bases
an
amphoteric substance
is any substance that can act as either an acid or a base, depending on the circumstances
Water can either accept a proton to become hydronium or can donate a proton to become hydroxide
Strength of Conjugate Pairs
a strong acid is a weak conjugate base
a strong base is a weak conjugate acid
Buffer
Neutralization
This is the type of reaction that occurs during a titration
Your body is an excellent buffer being able to absorb and release different ions to keep your blood's pH constant.
Autoionization
Water does this all on its own, randomly, all of the time.
Conjugate Acid-Base Pairs
An acid "falls apart" to make a hydrogen ion and a anion. Since the anion can accept an proton, it is a base by definition
Remember that
a salt
is a metal and a non-metal bonded together. Many salts exist, not just NaCl.
An acid is a substance that dissociates in water to produce hydrogen ions (H )
A base is a substance that dissociates in water to produce hydroxide ions (OH )
-
+
NaOH Na + OH
+
-
HCl H + Cl
+
-
An acid is a substance that can donate H ions
A base is a substance that can accept H ions
+
+
An acid is a substance that accepts a pair of electrons during a reaction
A base is a substance that donates an electron-pair during a reaction
AlCl + Cl AlCl
4
-
-
3
Lewis Acid
Lewis Base
H SO HCl HNO HI HBr HClO
2 4
3
4
ALL OTHER ACIDS ARE WEAK!
ALL OTHER BASES ARE WEAK!
Hydroxides of alkali and alkaline earth metals
HCl
Cl
-
water weakly dissociates into hydronium ions and hydroxide ions
H O H O + OH
2
3
+
-
There are equal numbers of and ions.
H O OH
3
+
-
At 25 C the and = 1.0 x 10 M
[H O ]
[OH ]
3
+
-
An acid and a base is formed from one another reversibly in a reaction.
the conjugates differ in composition by only a hydrogen atom.
HCl + H O
H O + Cl
3
+
-
2
Acid-conjugate pair: HCl and Cl
Base-conjugate pair: H O and H O
-
2
3
+
Chemical reaction between an acid and a base
that destroys the chemical characteristics of both!
it produces a salt and water
NaOH + HCl H O + NaCl
2
HCl +
H O

H O
+ Cl
3
+
-
2
Here
water
accepts a proton to act as
base
Here
water
donates a proton to act as an
acid
NH +
H O
NH +
OH
3
2
4
+
-
A buffer is a mixture of a acid and its weak conjugate base.

This mixture is able to absorb and release hydrogen ions in order to maintain the same pH
pH scale
the negative logarithm of the hydronium ion concentration in a solution
pH = -log[H O ]
3
+
10 = [H ]
-pH
+
Remember that the hydrogen ion and the hydronium ion are the same, as they only differ by a water.
-7
o
Hydrolysis of a Salt
when a salt dissolves in water it produces either
an
acidic
solution
a
basic
solution
a
neutral
solution
To make an
acidic
solution the
anion
must be that of a
strong acid
To make a
basic
solution the
cation
must be that of a
strong base
If both
ions
are present the solution is
neutral!
Brain Break!
Now switch as fast as you can so your left hand is on your right earlobe and your right hand is on your nose.
Hold your nose with your left hand and hold your left earlobe with your right hand.
Brain Break!
Turn sideways in your chair.
Make a number six with your right hand.
Move your right foot in a clockwise circle.
Brain Break!
Everyone Stand Up.
Using only knight moves, get everyone to sit down.
Titration
A
titration
is a carefully controlled acid base reaction that has the pH monitored while searching for the end point
the
endpoint
of the titration is the point where moles of acids equal moles of base
to find the concentration of an unknown acid or base, the dilution equation can be used.
-
Full transcript