Transcript Acids and Bases

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Acid and Bases
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Acid and Bases
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Acid and Bases
Some Household
Acids and Bases
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Acids
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Have a sour taste. Vinegar is a solution of acetic acid. Citrus
fruits contain citric acid.
Will react with certain metals to produce hydrogen gas.
Will react with carbonates and bicarbonates to produce carbon
dioxide gas.
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
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Some Properties of Acids
 Produce H+ (as H3O+) ions in water (the hydronium ion is a
hydrogen ion attached to a water molecule)
 Taste sour
 Corrode metals
 Electrolytes
 React with bases to form a salt and water
 pH is less than 7
 Turns blue litmus paper to red (red = acid)
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Some Properties of Bases
 Produce OH- ions in water
 Taste bitter, chalky
 Are electrolytes
 Feel soapy, slippery
 React with acids to form salts and water
 pH greater than 7
 Turns red litmus paper to blue
“Base = Blue”
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Some Common Bases
NaOH
sodium hydroxide
lye
KOH
potassium hydroxide
liquid soap
Ba(OH)2
barium hydroxide
stabilizer for plastics
Mg(OH)2
magnesium hydroxide “MOM” Milk of magnesia
Al(OH)3
aluminum hydroxide
Maalox (antacid)
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Reactions of acids and bases
HNO3 + KOH -> KNO3 + H2O
• A reaction between an acid and a base is a
type of double replacement reaction called
neutralization.
• In a neutralization reaction, water and a salt
are produced.
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Some Properties of Salts
• A salt is the combination of an anion (- ion) and a
cation (+ ion).
• Salts are products of the reaction between acids
and bases.
• Solid salts are usually crystalline.
• If a salt dissolves in water, it usually breaks up
into the ions that make up the salt.
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Strong Acids and Bases
• Strong acids are
those that break
apart (dissociate)
completely in
water.
• What does the
diagram on the
right show about
how strong acids
break apart?
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7 Strong Acids
HNO3 - nitric acid
HCl - hydrochloric acid
HBr - hydrobromic acid
HI - hydroiodic acid
H2SO4- sulfuric acid
HClO4 - perchloric acid
HClO3 - chloric acid
•Strong acids are assumed to ionize completely (100%)
in water. They exist as H3O+ ions in water. This is known
as “the leveling effect”.
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Strong Bases
LiOH - lithium hydroxide
NaOH - sodium hydroxide
KOH - potassium hydroxide
RbOH - rubidium hydroxide
CsOH - cesium hydroxide
Ba(OH)2 - barium hydroxide
Sr(OH)2 - strontium hydroxide
Ca(OH)2 - calcium hydroxide
GROUP 1
hydroxides
Some
GROUP 2
hydroxides
•In most cases, strong bases will also ionize completely
in water.
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Weak Acids and Bases
• Some acids and bases
ionize only slightly in
water.
• These are considered
weak.
• The most important
weak base is
ammonia.
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Balance of ions in acidic solutions
Acidic
Solution
Neutral
Solution
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ANIMATION LINKS
• Acid ionization equilibrium demo
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The pH scale is a way of
expressing the strength
of acids and bases
instead of using very
small numbers.
It ranges from 0-14.
Under 7 = acid
7 = neutral
Over 7 = base
pH of Common
Substances
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pH testing
• There are several ways to test pH
–Blue litmus paper (red = acid)
–Red litmus paper (blue = base)
–pH paper (multi-colored)
–pH meter (7 is neutral, <7 acid, >7
base)
–Universal indicator (multi-colored)
–Indicators like phenolphthalein
–Natural indicators like red cabbage,
radishes
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Indicators
Paper testing
• Paper tests like litmus paper and pH
paper
– Put a stirring rod into the solution
and stir.
– Take the stirring rod out, and
place a drop of the solution from
the end of the stirring rod onto a
piece of the paper
– Read and record the color
change. Note what the color
indicates.
– You should only use a small
portion of the paper. You can use
one piece of paper for several
tests.
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pH and Flowers
• For most big leaf hydrangeas, blue flowers
will be produced in acidic soil (pH 5.5 and
lower), whereas neutral to alkaline soils (pH
6.5 and higher) will usually produce pink
flowers. Between pH 5.5 and pH 6.5, the
flowers will be purple (see image at right) or a
mixture of blue and pink flowers will be found
on the same plant.
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Conjugate acid-base pairs
Neutralization reaction example:
HCl + HOH ↔ H3O+ + Cl¯
• Notice that each pair (HCl and Cl¯ as well
as HOH and H3O+ differ by one hydrogen
ion (H+).
These pairs are called conjugate pairs.
Example: HNO3 + HOH ↔ H3O+ + NO3¯
• What is the conjugate base to the acid
HNO3? What is the conjugate acid to the
base HOH? What are the pairs?
WHAT IS A BUFFER?
• A buffer solution is one which resists
changes in pH when small quantities
of an acid or a base are added to it.
• How do buffer solutions work?
A buffer solution has to contain
things which will remove any
hydrogen ions or hydroxide ions that
you might add to it - otherwise the pH
will change.
• buffer demo
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Definition of Acid Rain
• Precipitation that has a pH less than that of
natural rainwater (which is about 5.6 due to
dissolved carbon dioxide).
• It is formed when sulfur dioxides and nitrogen
oxides (gases or fine particles in the atmosphere)
combine with water vapor and precipitate as
sulfuric acid or nitric acid in rain, snow, or fog.
What Causes Acid Rain?
Natural Sources
-Emissions from volcanoes and from biological
processes that occur on the land, in wetlands, and in
the oceans contribute acid-producing gases to the
atmosphere
-Effects of acidic deposits have been detected in glacial
ice thousands of years old in remote parts of the globe
The principal cause of acid rain is from human sources
-Industrial factories, power-generating plants and
vehicles
-Sulfur dioxide and oxides of
nitrogen are released during
the fuel burning process
(i.e. combustion)
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How Does Acid Rain Form?
Formation of Acid Rain
• When water vapor condenses, or as the
rain falls, the gases and particles dissolve
in the water to form sulfuric acid (H2SO4)
and nitric acid (HNO3).
• While the air is cleansed of the pollutants in
this way, it also causes precipitation to
become acidic, forming acid rain.
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Formation of Acid Rain
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What Areas Are Most Affected?
• Canada -Water and soil systems lack
natural alkalinity such as lime base and
cannot neutralize acid
• Industrial acid rain is a substantial problem
in China, Eastern Europe and Russia and
areas down-wind from them.
• Acid rain from power plants in the Midwest
United States has also harmed the forests
of upstate New York and New England.
NOTE: This shows that the effects of
acid rain can spread over a large area,
far from the source of the pollution
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Effects of Acid Rain
• Harmful to aquatic life
–Increased acidity stops eggs of certain
organisms (e.g. fish) from hatching
–Changes population ratios and affects the
tissues of sensitive organisms
• Harmful to vegetation
- Increased acidity in soil
–Removes nutrients from soil, slowing plant
growth
–Dissolves toxins from soil, poisoning plants
–Creates brown spots in leaves of trees,
impeding photosynthesis
–Allows pests to infect vegetation through
broken leaves
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Effects of Acid Rain
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• Harmful to buildings
-Accelerates weathering in metal and stone
structures, and roads
-Ex: Parthenon in Athens, Greece; Taj Mahal in
Agra, India
• Harmful to human health
–Respiratory problems, asthma, dry coughs,
headaches and throat irritations
–Leeching of toxins from the soil by acid rain
can be absorbed by plants and animals.
When consumed, these toxins affect humans.
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Effects of Acid Rain
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What can we do?
• Reduce amount of sulfur dioxide and oxides of
nitrogen released into the atmosphere
– Use less energy (less fuel burned)
– Use cleaner fuels that contain less sulfur
– Remove oxides of sulfur and oxides of
nitrogen before releasing
– Use other sources of energy such as solar,
geothermal, nuclear, wind,
etc… (more expensive)
– Liming: powdered limestone
or limewater added to water
and soil to neutralize acid
(expensive)
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CAPT Activity: Brownfields
• Link to North Haven Pharmacia and Upjohn
LLC site:
• http://www.upjohnnorthhaven.com/backgroun
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