Transcript [H 3 O + ] & [OH

Finding pH
Chapter 14 – Acids and Bases
4. Which of the following metals does
not react with hydrochloric acid?
A.
B.
C.
D.
Calcium
Copper
Magnesium
Zinc
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Acid Properties
 Sour
taste (grape fruit)
 Found in many fruits
 Vinegar
 Will burn if not diluted
 Made up of Nonmetals
 Acid formulas usually start with
hydrogen- ex HCl, H2SO4
Base Properties
 Bitter
taste
 Slippery feel
 Most household cleaners
 Also dangerous if not diluted
 Made up of a metal and nonmetals in
formulas
 Arrhenius bases start with metals in
their formulas and end with a OH- ex
NaOH, KOH, Ba(OH)2
Arrhenius Theory
Acids release hydrogen ions
+
(H )
+
HCl → H + Cl
Bases release hydroxide
ions (OH )
+
NaOH → Na + OH
Strong Acids will completely ionize
7
Know the strong
acids & bases!
Brønsted-Lowry Theory D7C20
ACID: any substance that donates
a proton (hydrogen ion)
 BASE: any substance that accepts a
proton (hydrogen ion)

 MUST
occur together; Can not gain
unless something else loses
Differ by ONLY H+
Chemical Reactions: New products are formed
Brønsted-Lowry Theory
+ H2O → H3O+ + Clacid base
C.A.
C.B.
 Conjugate acid –the PRODUCT
obtained after a BASE gains a proton
(hydrogen ion)
 Conjugate base –the PRODUCT
obtained after an ACID donates a proton
(hydrogen ion)
 HCl
Conjugate Pairs
 Hydronium
ion – An ion formed
+
when a free H forms with water
+
to form an H3O
Why is Water Neutral?
[H3O+ ] = [OH-]
When one water gains,
another loses a H+
Water
AUTOIONIZATION
H2O can function as both an ACID
and a BASE.
Equilibrium constant for water
= Kw
Kw = [H3O+] [OH-] =
1.00 x 10-14 at 25 oC
14
Water
15
OH-
H3O+
Autoionization
Kw = [H3O+] [OH-] = 1.00 x 10-14 at 25 oC
In a neutral solution [H3O+] = [OH-]
so [H3O+] = [OH-] = 1.00 x 10-7 M
Kw = 1.00 x 10-14 ONLY at 25 oC (depends on T)
[H3O+], [OH-] and pH
A common way to express acidity and basicity
is with pH
pH = - log [H3
+
O ]
In a neutral solution,
[H3O+] = [OH-] =
1.00 x 10-7 at 25 oC
pH = -log (1.00 x 10-7)
= - (-7) = 7
16
The pH scale
only for water
solutions
Basic = more OHNeutral H3O+ = OHAcidic = more H3O+
Why at a pH = 7 ?

Determined by concentration [ X ] of each ion
[H+ ]= [OH-] = 10-7M
The concentration of hydrogen ion
equals the concentration of
hydroxide ion equals ten to the
negative seventh molar
concentration
Need to remember molarity and concentration
Any pX Scales
In general
pX = -log X
pOH = - log
pH = - log
[OH ]
+
[H ]
Determining pOH
pH + pOH = 14
If know one can determine
the other.
If pH = 13, what is the pOH?
13 + pOH = 14
pOH = 14 – 13 = 1
[H3O+],
[OH-]
and pH
What is the pH of 0.0010 M NaOH(aq)?
[OH-] = 1.0 x 10-3 M
[H3O+] = 1.0 x 10-11 M
pH = - log (1.0 x 10-11) = 11.00
General conclusion —
Basic solution pH > 7
Neutral
pH = 7
Acidic solution pH < 7
21
[H3O+], [OH-] and pH
ACID
If the pH of Coke is 3.12, it is ________.
log [H3O+] = - pH = - 3.12
Take antilog and get
[H3O+] = 10-pH
[H3O+] = 10-3.12 =
7.6 x 10-4 M
22
Calculate pH
IF [OH-] = 4.2 x 10-4 M
so pOH = - log [OH-] = 3.37
pH + pOH = 14,
pH = 10.63
23
SAMPLE PROBLEM

14.7
Calculating pH
Determine the pH for a solution with [H3O+] = 5 ´ 10–8 M.
SOLUTION
STEP 1
Press the log key Enter the [H3O+] value.
STEP 2
STEP 3
change the sign.
Adjust the number of significant figures on the right of the decimal
point
to equal the SFs in the coefficient.
© 2011 Pearson Education, Inc.
 Calculating [H3
SAMPLE PROBLEM
O+]
14.9
from pH
Calculate [H3O+] for a solution of baking soda with a pH
of 8.25.
STEP 1 Change the sign of pH
STEP 2 enter the negative pH as the exponent : 10 -pH
STEP 3 Write the display with units of concentration
5.62341 × 10–9 M
Adjust the significant figures in the coefficient. Because the pH
value of 8.25 has two digits on the right of the decimal point, the
[H3O+] is written with two significant figures:
[H3O+] = 5.6 * 10–9 M
Chapter 14 – Acids and Bases
9. What is the [H+] of a solution at pH 3.5?
A.
B.
C.
D.
5.3 x 10-5
6.0 x 10-4
3.16 x 10-4
8.84 x 10-3
© 2011 Pearson Education, Inc.
Calculating
[H3O+]
&
[OH-]
28
0.0010 mol of NaOH ia added to
1.0 L of pure water: Calculate
[H3O+] and [OH-].
NaOH → Na+ + OH-
[NaOH] = [OH-]= 1.0 * 10–3 M
[OH-] = 10
-3
M
than
pOH = 3.00
pH = 14 – 3.00 = 11.00
[H3O+] = 1.0 * 10 -11 M
Determining
+
[H3O ]
If pH = 6 than [H3O+] = 10 -6 M.
 The pH value is the negative
exponent for the concentration
of hydrogen ions in solution.
If pH = Y than [H3O+] = 10
-Y
M
Determining
[OH ]
If pOH = 10 than [OH-] = 10
-10
M
 The
value of pOH is used as the
negative exponent for the
concentration of the hydroxide
ions in solutions .
pOH = X than [OH-] = 10
-X
M