Transcript The Acid Test

The Acid Test
Acids, Bases and pH
2. Describe the pH Scale
The next few slides will illustrate
this point. Be sure to write small
and get it all!
Range of pH scale
•The pH scale ranges
from 0 to 14.
•There are no units of
measure for pH *
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+]
Learning Check pH7
Identify each solution as
1. acidic
2. basic
3. neutral
A. _____
HCl with a pH = 1.5
B. _____
Pancreatic fluid pH = 8
C. _____
Sprite soft drink pH = 3.0
D. _____
pH = 7.0
E. _____
pH = 3
F. _____
pH = 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 pH = 8
C. _1__
Sprite soft drink pH = 3.0
D. _3__
pH = 7.0
E. _1__
pH = 3
F. _2__
pH = 12
3. What is a hydronium ion?
Occasionally, in water, a H+ is transferred
between H2O molecules
..
..
H:O: +
:O:H
..
H
..
H
water molecules
..
H:O:H +
..
..
+ :O:H-
..
H
hydronium
ion (+)
hydroxide
ion (-)
4. How can the pH of a
solution be determined?
There will be several slides
showing various ways to measure
pH. Be sure to get them all!
Litmus paper
• 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
5. What are the properties of an
acid?
•
•
•
•
•
•
•
•
Acids
Taste sour
Donate a H+
pH less than 7
Turn litmus paper red
Turn bromothymol blue to yellow
Turn phenolphthalein colorless
Neutralize bases
6. What are the properties of
bases?
•
•
•
•
•
•
•
•
•
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 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*
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*
7. What compounds are formed
when an acid reacts with a base?
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*
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*
8. Antacids
A practical use of the
neutralization process
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*
Which solution is more acidic the
one with a pH of 2 or the one with
a pH of 6?
To answer this we are going to
look at concentration and its
effects on the environment.
pH measures the concentration of
hydrogen ion [H+] in a solution
• So every time you increase one number
on the pH scale the acidity (or alkalinity)
increases by a power of 10!
• The concentration of pH = 2 solution is 4
pH values from a pH = 6 solution or
• The pH = 2 solution is 10,000 times more
acidic than the pH = 6 solution
What does this mean for the
environment?
An in-depth look at acid rain
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*