Download - The Acid Test
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The Acid Test
Acids, Bases and pH
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2. Describe the pH Scale
The next few slides will illustrate this point. Be sure to write small
and get it all!
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Range of pH scale
•The pH scale ranges from 0 to 14.
•There are no units of measure for pH *
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pH Range
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutral
[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]
Acidic Basic
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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
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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
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3. What is a hydronium ion?
Occasionally, in water, a H+ is transferred between H2O molecules
. . . . . . . .H:O: + :O:H H:O:H + + :O:H-
. . . . . . . . H H H
water molecules hydronium hydroxide ion (+) ion (-)
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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!
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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*
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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. *
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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
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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 solution holds a very faint pink color for half a minute or more.
•alizarin yellow R •yellow •9.9 - 11.8 •dark orange
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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.*
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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
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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*
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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*
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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*
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Learning Check AB1
Describe the solution in each of the following as: 1) acid 2) base or 3)neutral.A. ___soda
B. ___soapC. ___coffeeD. ___ wineE. ___ water
F. ___ grapefruit*
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Solution AB1
Describe each solution as: 1) acid 2) base or 3) neutral.A. _1_ soda
B. _2_ soapC. _1_ coffeeD. _1_ wineE. _3_ water
F. _1_ grapefruit*
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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) + HCl(aq) NaCl + H2O
base acid salt water
Ca(OH)2 + 2 HCl CaCl2 + 2H2Obase acid salt water*
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Learning Check N2
Select the correct group of coefficients for the
following neutralization equations
A. __ HCl + __ Al(OH)3 __AlCl3 + __
H2O
1) 1, 3, 3, 1 2) 3, 1, 1, 1 3) 3, 1, 1 3
B.__ Ba(OH)2 + __H3PO4 __Ba3(PO4)2 + __ H2O
1) 3, 2, 2, 2 2) 3, 3, 1, 6 3) 2, 3, 1, 6
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Solution N2
A. 3HCl + 1Al(OH)3 1AlCl3 + 3H2O
B. 3Ba(OH)2 + 2H3PO4 1Ba3(PO4)2 +
6H2O*
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8. Antacids
A practical use of the neutralization process
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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*
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More Antacids
Milk of Magnesia: Mg(OH)2
Rolaids: AlNa(OH)2CO3
aluminum sodium dihydroxy carbonate
Tums: CaCO3
Tempo: CaCO3, Al(OH)3, Mg(OH)2*
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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.
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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
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What does this mean for the environment?
An in-depth look at acid rain
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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*
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Acid Rain
2. Reactions in the atmosphere form SO3
2SO2 + O2 2 SO3*
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Acid Rain
3. Reactions with atmosphere water form acids
SO3 + H2O H2SO4 sulfuric acid
NO + H2O HNO2 nitrous acid
HNO2 + H2O HNO3 nitric acid*
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Acid Rain4. 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*
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Sources of Acid Rain
Power stations
Oil refineries
Coal with high S content
Car and truck emissions
Bacterial decomposition, and lighting
hitting N2*