Transcript Chapter 10

The Acid Test
Acids, Bases and pH
Range of pH scale
 The
pH scale ranges
from 0 to 14.
 There are no units of
measure for pH *
What do the numbers mean?
A pH of 7 is neutral
 Pure water has a pH
of 7*

How about below 7?
 Anything
below 7 is acidic
 0 is the most acidic and
6.99999 is the least acidic
 The further something is from
7 the more acidic it is*
How about above 7?


higher than 7 is
basic/alkaline
So 7.000001 is a weak
base and 14 is the most
basic (or alkaline)*
pH Range
0
1
2
3 4 5
6
7 8 9 10 11 12 13 14
Basic
Acidic
Neutral
[H+]>[OH-]
[H+] = [OH-]
[OH-]>[H+]
The pH Scale
 pH
measures
acidity and
alkalinity
(how
basic) a
liquid is*
Ionization of Water
Occasionally, in water, a H+ is transferred
between H2O molecules
..
H:O: +
..
H
..
..
..
:O:H
H:O:H +
+
..
H
..
:O:H..
H
water molecules hydronium hydroxide
ion (+)
ion (-)
Measuring pH
Litmus paper, pH paper, and pH
meters*
Litmus paper
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Litmus paper cannot
tell you the exact pH
of a substance.
It can only tell you if
it is an acid or a base
Blue litmus turns pink
in the presence of an
acid
Red litmus turns blue
in the presence of a
base*
pH paper


pH paper can tell you
approximate pH
values.
By placing one end of
the pH paper in the
solution it will turn a
color which can be
matched to the color
code key. *
Indicators
•Indicators:
•Weak organic acids and bases whose
colors differ from the colors of their
conjugate acids or bases.
•The color is best viewed from above
against a white background
Table of Indicators
•
•Acid / Base Indicators
•Indicator
•Lower Color
•pH Range
•Upper Color
•methyl violet
•yellow-green
•0.0 - 2.5
•violet
•methyl orange
•red
•2.5 - 4.4
•yellow
•congo red
•blue
•3.0 - 5.0
•red
•bromocresol green
•yellow
•4.5 - 5.5
•blue
•methyl red
•red
•4.8 - 6.0
•yellow
•bromocresol purple
•yellow-green
•5.4 - 6.8
•violet
•bromothymol blue
•yellow
•6.0 - 7.6
•blue
•phenol red
•yellow
•6.4 - 8.2
•red-violet
•cresol red
•yellow
•7.1 - 8.8
•violet
•phenolphthalein
•colorless
•8.3 - 10.0
•dark pink
•Phenolphthalein is a common indicator to use in neutralization titrations. The solution is considered neutral when the soluti on holds a very faint pink color for half a minute or more.
•alizarin yellow R
•yellow
•9.9 - 11.8
•dark orange
pH Meter



The most precise and
usually more accurate
way to measure pH is
using a pH meter which
directly measures the
amount of [H3O+] in the
solution
Uses an electrode which
specifically measures
the pH of the solution.
This is a larger model.
Some are small enough
to be hand-held.*
What is an Acid?
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Sour Taste (We never taste chemicals in lab)
release hydrogen (H+)
React with metals to release H2
React with a base to produce water and a salt
(neutralization reaction)
Some that completely dissociate conduct current
(electrolytes)
Turns blue litmus paper red*
Naming Acids
Binary (begin with hydro-)
Oxyacids do not have hydro- *
Naming Binary Acids
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Binary acids contain hydrogen and one
other element
Binary acids begin with hydroBinary acids end with –ic*
Test your naming skills of these
acids
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HF
HCl
HBr
HI
H2S
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Hydrofluoric acid
Hydrochloric acid
Hydrobromic acid
Hydroiodic acid
Hydrosulfuric acid*
Oxyacid
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An acid that is a compound of hydrogen,
oxygen and a third element (usually a
nonmetal)
These do not contain hydroCan end in either –ic or –ous*
Name these Oxyacids
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CH3COOH
H2CO3
HIO3
HClO
HClO2
HClO3
HClO4
HNO2
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Acetic acid
Carbonic acid
Iodic acid
Hypochlorous acid
Chlorous acid
Chloric acid
Perchloric acid
Nitrous acid*
Name these oxyacids
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HNO3
H3PO4
H3PO3
H2SO4
H2SO3
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Nitric acid
Phosphoric acid
Phosphorous acid
Sulfuric acid
Sulfurous acid*
Common Industrial Acids
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Sulfuric
Nitric
Phosphoric
Hydrochloric
Acetic *
Sulfuric
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Most commonly produced acid worldwide
Petroleum refining
Metallurgy
Fertilizer manufacturing
Production of metal, paper, paint, dyes,
detergents
Automobile batteries*
Sulfuric Acid
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Can be used to dehydrate (water removing)
Sugar can be dehydrated by this acid
Has the same effect on organic tissue
causing severe burns *
Nitric Acid
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Volatile and unstable in its pure form
Rarely used in its pure form
Stains yellow and burns skin
Used in the making of explosives rubber,
plastics, dyes and pharmaceuticals *
Phosphoric Acid
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Manufacture of fertilizer and animal feed
Flavoring agent in dilute form
Cleaning agent for dairy equipment
Manufacture of detergents and ceramics*
Hydrochloric acid
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Produced in your stomach to aid in
digestion
Used to remove surface impurities of
metals (iron and steel)
Cleaning agent in food industry
Also known as muriatic acid in a dilute
form
Adjust the pH of Swimming pools*
Different Definitions of Acids and
Bases
Arrhenius
Bronsted-Lowry
Lewis*
Arrhenius Acids and Bases
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Arrhenius acid is a chemical compound
that increased the concentration of H+ in an
aqueous solution
Arrhenius base is a chemical that increases
the concentration of OH- ions in an
aqueous solution *
Characteristics of Acids and Bases
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Acids
Taste sour
Donate a H+
pH less than 7
Turn litmus paper red
Turn bromothymol
blue to yellow
Turn phenolphthalein
colorless
Neutralize bases
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Bases
Taste bitter
Usually ends in -OH
pH greater than 7
Turn litmus paper
blue
Turn bromothymol
blue to blue
Turn phenolphthalein
pink
Feel slippery to touch
Neutralize acids*
Learning Check AB1
Describe the solution in each of the following
as: 1) acid 2) base or 3)neutral.
A. ___soda
B. ___soap
C. ___coffee
D. ___ wine
E. ___ water
F. ___ grapefruit*
Solution AB1
Describe each solution as:
1) acid 2) base or 3) neutral.
A. _1_ soda
B. _2_ soap
C. _1_ coffee
D. _1_ wine
E. _3_ water
F. _1_ grapefruit*
Learning Check AB2
Identify each as characteristic of an A) acid
or B) base
____ 1. Sour taste
____ 2. Produces OH- in aqueous solutions
____ 3. Chalky taste
____ 4. Is an electrolyte
____ 5. Produces H+ in aqueous solutions*
Solution AB2
Identify each as a characteristic of an A) acid
or B) base
_A_ 1. Sour taste
_B_ 2. Produces OH- in aqueous solutions
_B_ 3. Chalky taste
A, B 4. Is an electrolyte
_A_ 5. Produces H+ in aqueous solutions*
Arrhenius Acids and Bases
 Acids produce H+ in aqueous solutions
water
H+(aq) + Cl- (aq)
HCl
 Bases produce OH- in aqueous solutions
water
NaOH
Na+(aq) + OH- (aq)*
Learning Check AB3
Give the names of the following
A. HBr (aq)
1. bromic acid
2. bromous acid
3. hydrobromic acid
B. H2CO3
1. carbonic acid
2. hydrocarbonic acid
3. carbonous acid*
Solution AB3
A. HBr
3. hydrobromic acid
The name of a nonoxy acid begins with the prefix
hydro- and ends with -ic acid. In a nonoxy acid,
the negative anion end in -ide.
B. H2CO3
1. carbonic acid
The name of an oxyacid is named with the stem
of the anion (carbonate) changed to
-ic acid *
Some Common Bases
NaOH
sodium hydroxide
KOH
potassium hydroxide
Ba(OH)2
________________________
Mg(OH)2
________________________
Al(OH)3
aluminum hydroxide*
Learning Check AB4
Match the formulas with the names:
A. ___
HNO2
1) hydrochloric acid
B. ___
Ca(OH)2
2) sulfuric acid
C. ___
H2SO4
3) sodium hydroxide
D. ___
HCl
4) nitrous acid
E. ___
NaOH
5) calcium hydroxide*
Solution AB4
Match the formulas with the names:
A. _4__ HNO2
1) hydrochloric acid
B. _5__ Ca(OH)2
2) sulfuric acid
C. _2__ H2SO4
3) sodium hydroxide
D. _1__ HCl
4) nitrous acid
E. _3__ NaOH
5) calcium hydroxide*
Learning Check AB5
Acid, Base Name
or Salt
CaCl2
______
_________________
KOH
______
_________________
Ba(OH)2
______
_________________
HBr
______
_________________
H2SO4*
______
__________________
Solution AB5
Acid, Base
or Salt
Name
CaCl2
salt
calcium chloride
KOH
base
potassiuim hydroxide
Ba(OH)2 base
barium hydroxide
HBr
acid
hydrobromic acid
H2SO4
acid
sulfuric acid*
Bronsted-Lowry Acids
Acids are hydrogen ion (H+) donors
Bases are hydrogen ion (H+) acceptors
HCl
+
donor
H2O
acceptor
+
H3O+
+
+
Cl-
+
Strengths of Acids and Bases
Strong acids completely ionize (100%) in aqueous
solutions
HCl + H2O
H3O+ + Cl- (100 % ions)
Strong bases completely (100%) dissociate into ions
in aqueous solutions.
NaOH
Na+ (aq) + OH-(aq)
(100 % ions)*
NH3, A Bronsted-Lowry Base
When NH3 reacts with water, most of the
reactants remain dissolved as molecules, but a
few NH3 reacts with water to form NH4+ and
hydroxide ion.
NH3
+ H2O
acceptor
NH4+(aq) + OH- (aq)
donor
+
+
Strong and Weak
Acids and Bases
Strong acids
HCl, HNO3 , H2SO4
Most other acids are weak.
Strong bases
NaOH, KOH, and Ca(OH)2
Most other bases are weak.*
Learning Check SW1
Identify each of the following as a
1) strong acid or base 2) weak acid
3) weak base
A. ___ HCl (aq)
B. ___ NH3(aq)
C. ___ NaOH (aq)
D. ___ H2CO3 (aq)
Solution SW1
Identify each of the following as a
1) strong acid or base 2) weak acid
3) weak base
A. _1__ HCl (aq)
B. _3__ NH3(aq)
C. _1__ NaOH (aq)
D. _2__ H2CO3 (aq)*
Antacids
Used to neutralize stomach acid (HCl)
Many contain one or more weak bases
Alka-Seltzer:
NaHCO3, citric acid, and aspirin
Di-gel:
CaCO3 and Mg(OH)2
Gelusil:
Al(OH)3 and Mg(OH)2
Maalox:
Al(OH)3 and Mg(OH)2
Mylanta:
Al(OH)3 and Mg(OH)2*
More Antacids
Milk of Magnesia:
Rolaids:
Mg(OH)2
AlNa(OH)2CO3
aluminum sodium dihydroxy carbonate
Tums:
CaCO3
Tempo:
CaCO3, Al(OH)3, Mg(OH)2*
Types of Acids
Monoprotic
Diprotic
Polyprotic *
Monoprotic
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An acid that donates one proton
HCl
CH3COOH (the H on the end is donated)*
Diprotic
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Donates two protons
Ex. H2SO4*
Polyprotic
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Donates more than two hydrogen atoms
Ex. H3PO4*
Lewis Acids and Bases
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Lewis Acid: atom, ion, or molecule that
accepts an electron pair to form a covalent
bond
Lewis Base: atom, ion, or molecule that
donates an electron pair to form a covalent
bond *
Concentrations
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In lab, our concentrations are marked like
this 0.01 M
M = concentration of moles per liter
The bigger the number the higher the
concentration.
Which one is a stronger concentration?
0.001 M or 0.1M? *
Dilutions
 Add water
 Volume increases.
 New concentration is less than initial*
Concentration of A Diluted
Solution
A 25 mL sample of a 6.0 M KOH is diluted by adding
75 mL of water. Calculate the new concentration of the
KOH solution.
Moles KOH = 0.025 L x 6.0 moles = 0.15 moles
1L
New volume = 25 mL + 75 mL = 100. mL = 0.100 L
New molarity = 0.15 moles = 1.5 M*
0.100 L
Learning Check SW 2
A 125 mL sample of a 3.0 M HCl is diluted by
adding 250 mL of water. The new
concentration of the HCl solution is
1) 8.0 M
2) 1.5 M
3) 1.0 M*
Solution SW 2
3) 1.0 M
moles HCl = 0.1250 L x 3.0 moles = 0.375 mole
1L
new M = 0.375 mole
0.3750 L
(new volume)*
1.0 M HCl
Learning Check SW 3
A 50.0 mL sample of 15% sucrose solution is
diluted by adding 200. mL of water. The new
concentration of the sucrose solution is
1) 3.0 %
2) 7.5 %
3) 10. %*
Learning Check SW 3
A 50.0 mL sample of 15% sucrose solution is
diluted by adding 200. mL of water. The new
concentration of the sucrose solution is
1) 3.0 %
g sucrose = 50.0 mL x 15 g sucrose = 7.5 g
100 mL
new % = 7.5 g sucrose
= 3.0 % sucrose
250 mL
(new volume) *
Neutralization Reactions
When acid and bases with equal amounts of
hydrogen ion H+ and hydroxide ions OH- are
mixed, the resulting solution is neutral.
NaOH (aq)
base
+ HCl(aq)
acid
NaCl + H2O
salt
water
Ca(OH)2
base
+ 2 HCl
acid
CaCl2 + 2H2O
salt
water*
Neutralization
H3O+ and OH- combine to produce water
H3O+
+
from acid
OH-

from base
2 H2O
neutral
Net ionic equation:
H+
+
OH-

H2O*
Ionic Equations for Neutralization
Write strong acids, bases, and salt as ions
H+ + Cl- + Na+ + OH-
Na+ + Cl- +
H2O
Na+ + Cl- +
H2O
Cross out matched ions
H+ + Cl- + Na+ + OH-
Write a net ionic reaction
H+ +
OH-
H2O*
Balancing Neutralization Equations
Write the equation for the neutralization between
magnesium hydroxide and nitric acid.
1. Write the formulas of the acid and base
Mg(OH)2
+
HNO3
2. Balance to give equal OH- and H+
Mg(OH)2
+
2 HNO3*
3. Write the products:
Mg(OH)2
+ 2HNO3
Mg(NO3)2 + H2O
salt
water
(metal and nonmetal)
4. Balance products
Mg(OH)2
+ 2 HNO3
Mg(NO3)2 + 2 H2O*
Learning Check N2
Select the correct group of coefficients for the
following neutralization equations
A.
__ HCl + __ Al(OH)3
1) 1, 3, 3, 1
2) 3, 1, 1, 1
B.__ Ba(OH)2 + __H3PO4
1) 3, 2, 2, 2
__AlCl3 + __ H2O
3) 3, 1, 1 3
__Ba3(PO4)2 + __ H2O
2) 3, 3, 1, 6
3) 2, 3, 1, 6
Solution N2
A. 3HCl + 1Al(OH)3
B. 3Ba(OH)2 + 2H3PO4
1AlCl3 + 3H2O
1Ba3(PO4)2 + 6H2O*
Learning Check N3
Write a balanced equation and calculate the
mL of 2.00 M H2SO4 required to neutralize
50.0 mL of 1.00 M KOH?
___H2SO4 + ___KOH
1) 12.5 mL
2) 50.0 mL
___K2SO4 + H2O
3) 200. mL*
Solution N3
How many mL of 2.00 M H2SO4 are required to
neutralize 50.0 mL of 1.00 M KOH?
H2SO4 + 2KOH
K2SO4 + 2H2O
0.0500 L x 1.00 mole KOH x 1 mole H2SO4 x
1L
1L
x
2 mole KOH
2 mole KOH
1000 mL =
1L*
12.5 mL
Learning Check N4
A 25 mL sample of phosphoric acid is
neutralized by 40. mL of 1.5 M NaOH. What is
the molarity of the phosphoric acid solution?
3NaOH + H3PO4
1) 0.45 M
Na3PO4 + 3H2O
2) 0.80 M
3) 7.2 M*
Solution S4
0.040 L x 1.5 mole NaOH x 1 mole H3PO4
1L
x
1
0.025 L***
3 mole NaOH
= 0.80 mol/L = 0.80 M*
Logarithms and pH Calculations
Scientific Notation Review
Log Review (or Introduction)
pH formulas
pH calculations
Pure Water is Neutral
Pure water contains small, but equal amounts of
ions: H3O+ and OH-
H3O+
H2O + H2O
H3
O+
OH-
ion
+
OH-
hydronium hydroxide
ion
1 x 10-7 M 1 x 10-7 M*
Acids

Increase H+

HCl (g) + H2O (l)

More [H3O+] than water > 1 x 10-7M

As H3O+ increases, OH- decreases
[H3O+] > [OH-]*
H3O+ (aq) + Cl- (aq)
H 3O +
OH-
Bases
Increase the hydroxide ions (OH-)
H2 O
NaOH (s) Na+(aq) + OH- (aq)
More [OH-] than water, [OH-] > 1 x 10-7M
 When OH- increases, H3O+ decreases
[OH] > [H3O+]*
H 3O +
OH-
Using logarithms and scientific
notation

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Logarithms also called logs are exponents
Log of (1 x 10-14) = -14
Log of 0.001 = 1 x 10-3 = -3
You can also take the –log which would be
–log 0.00001 = -log 1 x 10-5 = -(-5) = 5*
Using the Calculator
1.0 x 10 -14
4.0 x 10-5
Enter 1.0 EE +/- 14  4.0 EE +/- 5
= 2.5 x 10 –10*
pH
 Indicates the acidity [H3O+] of the solution
 pH = - log [H3O+]
 From the French pouvoir hydrogene
(“hydrogen power” or power of
hydrogen)*
pH
In the expression for [H3O+]
1 x 10-exponent
the exponent = pH
[H3O+] = 1 x 10-pH M*
Calculating pH
pH is found by using the formula
pH = - log [H3O+]



pH + pOH = 14
pOH = -log [OH-]*
pH on the Calculator
[H3O+] is 4.5 x 10-6 M
pH = 4.5 x EXP(or EE) 6+/- LOG +/= 5.35*
Applying logs to pH calculations
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If you have an acid with concentration of
0.01M what is the pH?
Answer: 0.01 = 1x10-2
pH = -log (1x10-2) =
-(-2) = 2*
Some [H3O+] and pH
[H3O+]
pH
1 x 10-5 M
5
1 x 10-9 M
9
1 x 10-11 M
11*
Applying concentration to base
pH

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
If you have a BASE with concentration of
0.0001 M what is the pH?
0.0001 = 1 x 10-4
pOH = -log (1x10-4) =-(-4) = 4 but this is
pOH,
so then we have to say pH + pOH = 14.
So pH + 4 = 14; thus, pH = 10.*
Learning Check pH4
A. The [H3O+] of tomato juice is 1 x 10-4 M.
What is the pH of the solution?
1) - 4
2)
4
3)
8
B. The [OH-] of an ammonia solution is
1 x 10-3 M. What is the pH of the solution?
1)
3
2)
11
3)
-11*
Solution pH4
A. pH = - log [ 1 x 10-4] = -(- 4) = 4
B. [H3O+] = 1 x 10-11
pH = - log [ 1 x 10- 11] = -(- 11) = 11*
Learning Check pH5
The pH of a soap is 10. What is the [H3O+] of the
soap solution?
1) 1 x 10 - 4 M
2) 1 x 1010 M
3) 1 x 10 - 10 M*
Solution pH5
The pH of a soap is 10. What is the [H3O+] of the
soap solution?
[H3O+]
= 1 x 10-pH M
= 1 x 10-10 M*
Learning Check pH6
A soap solution has a [H3O+] = 2 x 10-8 M. What is
the pH of the solution?
1) 8
2) 7.7
3) 6*
Solution pH6
A soap solution has a [H3O+] = 2.0 x 10-8
M. What is the pH of the solution?
B) 2.0 EE
8 +/- LOG +/- = 7.7*
Learning Check pH7
Identify each solution as
1. acidic
2. basic
3. neutral
A. _____
HCl with a pH = 1.5
B. _____
Pancreatic fluid [H+] = 1 x 10-8 M
C. _____
Sprite soft drink pH = 3.0
D. _____
pH = 7.0
E. _____
[OH- ] = 3 x 10-10 M
F. _____
[H+ ] = 5 x 10-12*
Solution pH7
Identify each solution as
1. acidic
2. basic
3. neutral
A. _1__
HCl with a pH = 1.5
B. _2__
Pancreatic fluid [H+] = 1 x 10-8 M
C. _1__
Sprite soft drink pH = 3.0
D. _3__
pH = 7.0
E. _1__
[OH-] = 3 x 10-10 M
F. _2__
[H+] = 5 x 10-12*
Acid Rain
Unpolluted rain has a pH of 5.6
Rain with a pH below 5.6 is “acid rain“
CO2 in the air forms carbonic acid
CO2 + H2O
H2CO3
Adds to H+ of rain
H2CO3
H+ (aq) + HCO3-(aq)*
Acid Rain
Formation of acid rain:
1. Emission of sulfur and nitrogen oxides from
the burning of fuels especially coal with high S
content, power stations, oil refineries, vehicles
as well as bacterial decomposition, and
lighting hitting N2
SO2
26 million tons in
1980
NO and NO2
22 million tons in
1980
Mt. St Helens (1980) 400,000 tons SO2*
Acid Rain
2. Reactions in the atmosphere form SO3
2SO2 + O2  2 SO3*
Acid Rain
3. Reactions with atmosphere water form
acids
SO3 + H2O  H2SO4 sulfuric acid
NO + H2O  HNO2 nitrous acid
HNO2 + H2O  HNO3 nitric acid*
Acid Rain
4. Effects of Acid Rain
Decline in fish populations in rivers and
lasts due to toxic effect of Al leached
from soil by acid rain
Extensive fish kills in spring from runoff
due to accumulation of large amounts of
acid on the snow
Dissolves minerals Mg, Ca, and K from
the soil and waxy coatings that protect
leaves from bacteria
Corrodes metals, textiles, paper and
leather*
Sources of Acid Rain
Power stations
Oil refineries
Coal with high S content
Car and truck emissions
Bacterial decomposition, and lighting hitting
N2*
Titration
Acids and Bases
Quantitative Analysis*
Acid/Base Titration


Titration is an analytical method in
which a standard solution is used to
determine the concentration of
another solution.
Any solution for which the
concentration is precisely known is
called a standard solution. *
Titration
Titration Movie
Before Endpoint
At the Endpoint—
Color persists for 30 s
after swirling
Over Titrated—
missed endpoint—
Start over!
Titrations (cont.)
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An acid/base titration uses the fact that one can be
"neutralized" with the other. In this neutralization
reaction, the acid and base will combine to produce a salt
plus water. When done correctly, the resulting solution
will be "neutral" - neither acid nor base. In a titration, this
is known as the end point. The change in pH of the
solution can be monitored using an indicator or pH
meter. It is extremely important that the exact amounts of
each solution used be known at the end point.
*
Titration Curve
This graph represents the
titration of 10 ml of 0.1M
HCl with 0.1M NaOH.
The end point is
characterized by a rapid
change in pH with very
little base added.
*
Titration Problem Example:
If 20 cm3 of a 0.3 M solution of NaOH is required to neutralize 30.0 cm 3 of a sulfuric acid solution, what is the molarity of the acid
solution?
Solution Steps:
1.Write a balanced equation: 2NaOH + H2SO4
Na2SO4 + 2H2O
2.Determine the number of moles of the standard NaOH solution used:
3.Use the mole ratio from the balanced equation
to convert moles of NaOH to moles of H2SO4:
4.Use the volume of acid solution used to determine the molarity of the acid solution:
Notice that the 1dm3/1000cm3 and the
these conversions.
1000cm3/
1dm
3
will offset each other. You may shorten the problem by skipping
THE END 