*THE AUTOIONIZATION OF WATER:

the reaction between two water molecules producing a ____________ ion and a __________ ion; takes place in all samples of water.
H
2
O
(l)
+ H
2
O
(l)
H
3
O +
(aq)
+ OH -
(aq)
*Abbreviation:
*H
2
O + proton = ______________ ion ; H
2
O – proton = ____________ ion

This reaction is extremely _______. On average, at 25

C, only about _______ water molecules in a billion are ionized at any given moment. At higher temperatures this number ______________.
THE ION PRODUCT CONSTANT OF WATER, K w
 The product of the molar concentrations of _______________ ion and _______________ ion in water is a
___________________ called the ion-product constant of water , K w
.
H
2
O
(l)
H +
(aq)
+ OH -
(aq)
K w
= [
(aq)
][
(aq)
]
K w
= ( mol dm -3 )( mol dm -3 )
K w
= *Remember: this is the magnitude of K w
at ______˚C / ______K
*Useful rearrangements of the K w
formula: [H +
(aq)
] = ; [OH -
(aq)
] =
The value of K w
is ____________________ dependent!
Temperature (˚C)
0
10
20
K w
1.5 x 10 -15
3.0 x 10 -15
6.8 x 10 -15
*25
30
40
*1.0 x 10 -14
1.5 x 10 -14
3.0 x 10 -14
50
60
5.5 x 10 -14
9.5 x 10 -14
*Use 1.0 x 10 -14 in calculations, unless otherwise stated.
NEUTRAL, ACIDIC, & BASIC SOLUTIONS IN TERMS OF [H +
(aq)
] AND [OH -
(aq)
]
In _______________ solutions: [H +
(aq)
] = [OH -
(aq)
] ; pH = 7.00 @ 25˚C
In _______________ solutions : [H +
(aq)
] > [OH -
(aq)
]; pH < 7.00 @ 25˚C
In _______________
*K w
= 10 solutions : [H +
(aq)
] < [OH -
(aq)
]; pH > 7.00 @ 25˚C
-14
, regardless of whether solution is acidic, basic or neutral…@ 25˚C.
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IMPORTANT FORMULAS: pH, pOH & pK w
*The pH concept was devised to make it easier to express and compare the concentration of H + ions when they have very
___________ (i.e. < 1 mol H + /L) values involving awkward exponential terms. pH pOH pK w pH = and
[H +
(aq)
]= pOH = and pK w
=
RECALL: K w
= [H +
(aq)
] [OH -
(aq)
*Take
–log
of each variable:
]
-logK w
= -log [H
Therefore:
[OH -
(aq) pK w
=
OR
+
(aq)
] + -log [OH -
(aq)
]
@ ______˚C /______K

(@ 25˚C):
+
(aq)
-
(aq)
+
(aq)
-
(aq)
2

*Complete the following:
1.
The pH scale is a logarithmic scale. What does this mean?
2.
The pH of a solution increases from 1 to 5. Explain what has happened to the hydronium ion concentration.
3.
Determine the pH and pOH of a: i) solution in which the hydronium ion concentration is 3.46 x 10 -4 mol dm -3 . *Report pH’s to 2 decimal places . ii) 0.25 mol dm -3 hydrochloric acid solution. iii) 2.0 molar dm -3 nitric acid solution. *What’s “strange” about your answer? iv) 0.50 mol dm -3 sodium hydroxide solution. v) 1.0 x 10 -3 mol dm -3 calcium hydroxide solution.
4. a) What is the hydroxide ion concentration in the solution from question 3 part i)? *Calculate this two different ways.
b) What is the hydronium ion concentration in the solution from question 3 part iv)?
c) What is the calcium ion concentration in the solution from question 3 part v)?
5.
Determine the pH of neutral water at: a) 0˚C. b) 60˚C. c) Is water acidic, basic or neutral at these temperatures? Explain.
6.
a) What type of acids & bases are present in question 3?...strong or weak? b) What must be known in order to determine the pH of a solution containing a WEAK acid or base?
ACID AND BASE DISSOCIATION CONSTANTS
*RECALL : Weak Acids

ionize______________ in aqueous solution
EXAMPLE 1 - A weak _________________ acid: ethanoic acid [CH
3
COOH hydrogen(s) is/are represented at the beginning of the chemical formula.]
*The ionization of ethanoic acid(a hydrolysis/water “splitting” Rxn):
*Abbreviation: *The
  
Acid Dissociation Constant

:

H C
2
H
3
O
2
- *The “acidic”
K a
=
*The values of K a
for various acids are not given directly in your Data Booklet. They have to be calculated from a pK a value. Look up the pK
a values on p.13 of your Data Booklet for the following acids. * Remember : pK a
= -logK a
ACID
Ethanoic acid pK a
K a
= 10 -pKa
Chloroethanoic acid
Trichloroethanoic acid
*List these three acids from strongest to weakest.

*IMPORTANT CONNECTIONS:
↓pK a
= ↑______ = ↑ %_______________ = _____________ acid = ↓______ (for a given concentration)
EXAMPLE 2 - A weak __________________ acid: carbonic acid ( H
2
CO
3
)
Ionization #1 : Ionization #2 :
Ka
1
=
=
K a1
> K a2
Ka
2
=
=
3

*RECALL: Weak Bases

react incompletely with water; have a weak attraction for protons
EXAMPLE : aniline, C
5
H
5
NH
2
The ionization/hydrolysis equation(Can’t abbreviate):
*The Base Dissociation Constant : K b
=
* pK b values found on p. 14 of Data Booklet. [pK b
= -logK b
; K b
= 10 -pKb ; The lower the pK b
, the stronger the base etc.]
*NOTE: Strong acids and bases do not have dissociation constants . Why?
ANOTHER IMPORTANT FORMULA:
a
b
w
*Show how this formula is derived.
*K w
=
*K w
is always 10 -14 (@298 K), therefore the larger the K a
, the smaller the K b
. In other words: the STRONGER THE
ACID, THE WEAKER ITS CONJUGATE BASE AND VICE VERSA.
*Use this new formula to determine the K b
of ammonia.
Ionization/hydrolysis equation:
Therefore:
K b
=
*
K w
K a
*K a
of the conjugate acid . K a
of _______ =
*SUMMARY OF IMPORTANT FORMULAS/RELATIONSHIPS USED TO SOLVE ACID/BASE PROBLEMS:
At 25° C pH pOH pH = -log[H + ] pOH = -log[OH ]
[H + ] = 10 -pH
[OH ] = 10 -pOH pK pK pK a b w pK pK a b
= -logK
= -logK a b
K w
= [H + ] [OH ] = 10 -14
K a
= 10 -pKa
K b
= 10 -pKb
K w
= (K a
)(K b
) = 10 -14 pK w
= pH + pOH = 14.00 pK w
= pK a
+ pK b
=14.00
AT ANY TEMPERATURE
K a
x K b
= K w
(@ specified temp.) pK a
+ pK b
= pK w pH + pOH = pK w
PRACTICE: CALCULATIONS INVOLVING K a
and K b
Nelson Text Q’s: * p. 532#1-3 ; p. 537 #4-7 ; p. 540 # 8-10 ; p. 546 #12-15 ; p.549 #17-19; 1-13 from the section 8.2.
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