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ACIDS AND BASES
ACIDSTaste sourTurn litmusReact with active
metals – Fe, Zn
React with bases
BASESTaste bitterTurn litmusFeel soapy or
slippery (react with fats to make soap)React with acids
GENERAL PROPERTIES
blue to red red to blue
Acids – produce H+
Bases - produce OH-
Acids – donate proton (H+)
Bases – accept proton (H+)
Acids – accept e- pair Bases – donate e- pair
DEFINITIONS
Arrehenius
Bronsted-Lowry
Lewis
only in water
any solvent
used in organic chemistry,wider range of substances
EXAMPLES
Arrhenius
Bronsted-Lowry
Lewis
HCl NaOH
HCl NH3
:NH3BF3
HCN
The hydrogen ion in aqueous solutionH+ + H2O H3O+ (hydronium ion)
THE BRONSTED-LOWRY CONCEPT
Conjugate pairs
HCl Cl- CH3COOH CH3COO-
NH4+ NH3 HNO3 NO3
-
How does a conjugate pair differ?H+ transfer
A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor
acid conjugate basebase conjugate
acid
CONJUGATE PAIRS
NEUTRALIZATION
In general: Acid + Base Salt + Water
All neutralization reactions are double displacement reactions.
HCl + NaOH NaCl + HOH
HCl + Mg(OH)2
H2SO4 + NaHCO3
H2O H+ + OH-
Does pure water conduct electrical current?
(H+)(OH-) = 10-14
For pure water: (H+) = (OH-) =
This is and at 25oC is a pH = 7.
Water is a very, very, very weak electrolyte.
How are (H+) and (OH-) related?
water
HA
Let’s examine the behavior of an acid, HA, in aqueous solution.
What happens to the HA molecules in solution?
HA
H+
A-
Strong Acid
100% dissociation of HA
Would the solution be conductive?
HA
H+
A-
Weak Acid
Partial dissociation of HA
Would the solution be conductive?
HA
H+
A-
Weak Acid
HA H+ + A-
At any one time, only a fraction of
the molecules are
STRONG AND WEAK ACIDS/BASES
Strong acids/bases – 100% dissociation into ions
HCl NaOHHNO3 KOHH2SO4
Weak acids/bases – partial dissociation, both ions and molecules
CH3COOH NH3
KW: THE ION-PRODUCT CONSTANT OF WATER
If water conducts electricity, ions must exist Water exists as an equilibrium, which is referred to
as the of water:H2O + H2O
Simplified reaction:
Kc =[H3O+] [OH–]
[H2O]2Kw =or
Note: H+ is just shorthand for H3O+
Kc =[H+] [OH–]
[H2O]Kw =or
KW What is the value of Kw?
It has been measured at
To determine the pH of a substance we look for the following relationship between [H+] and [OH-]:
when the solution isacidicbasic
neutral
Pure water is neutral since [H+] and [OH–] must be
PH When there is a change in [H+] it is by
a change in [OH–], since Kw is constant, and must always equal
[H+] is commonly referred to because it is critical to chemical and biochemical reactions
A quick method of denoting [H+] is via pH By definition
The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of ‘6’ is as violent as a ‘5’
Thus, the pH scale condenses possible values of [H+] to a
CALCULATIONS WITH PH pH = – log [H+], what is pH if [H+] = 6.3 x
10–5?
• What is [H+] if pH = 7.4?• To solve this we must rearrange our equation
[H+] = 10–pH mol/L
EQUATIONS AND PRACTICE
pH =
• You will need to memorize the following:
pOH =
[H+] = [OH–] =
pH + pOH =
MEASURING PH pH can be measured in several ways Usually it is measured with a
Colored indicators are a crude measure of pH, but are useful in certain applications
MEASURING PH pH meters are more
accurate, but they must be calibrated prior to use
Calibration means setting to a
A pH meter is calibrated with a solution of known pH often called a
When life goes either wayamphoteric (amphiprotic) substances
HCO3-
H2CO3 CO3-2
+ H+ - H+
Acting like a base
Acting like an acid
accepts H+ donates H+
Show how water can be amphoteric.
H2O
+ H+ - H+
Dilutionwater (solvent) solute
concentrated, Minitial
diluted, Mfinal
adding water lowers the solute concentration
moles of solute remain constant
Vinitial
Vfinal
molesinitial = molesfinal
Titration CalculationHCl + NaOH NaCl + HOH
at equivalence point: moleHCl = moleNaOH
A way to analyze solutions!
indicator