2.4 Acids and Bases
These reactions prevent any
significant change in blood pH.
Forests are also damaged when toxic chemicals
such as aluminum are leached from the soil.
When fossil fuels such as coal, oil, and gasoline are burned,
sulfur dioxide and nitrogen oxides combine with water to produce sulfuric and nitric acids.
Forest on mountaintops receive more rain than those at lower levels;
therefore, they are more affected by acid rain.
These pollutants are generally found eastward of
where they originated because of wind patters.
Methyl mercury accumulates in fish,
which wildlife and people eat.
These kill soil fungi that assist roots in
acquiring the nutrients trees need.
The Impact of Acid Deposition Acid Deposition: Normally, rainwater has a pH of about 5.6 because the
carbon dioxide in the air combines with water to give a weak solution of carbonic acid.
What do they have in common?
Acids are substances that dissociate in water, releasing hydrogen ions (H+).
Biological Systems
All of life consists of systems, from the atomic and molecular levels to the ecosystem and planet levels.
Summarize how buffers play an important role in the physiology of living organisms.
Buffers help the body maintain a constant pH, preventing it from getting to acidic or to basic.
Biological Systems
Cells consist largely of water, a molecule that contains only hydrogen and oxygen atoms. Because of oxygen's strong electronegativity, water is a polar molecule, making hydrogen bonding possible.
The paint on homes and automobiles is like wise degraded.
However, damage to natural systems and human structures due to acid rain is likely to decrease if we continue efforts to reduce chemicals that contribute to acid rain.
Some bases from weakest to strongest.
Human blood, egg whites, seawater, baking soda, stomach antacids, Great Salt Lake, household ammonia, bicarbonate of soda, oven cleaner, sodium hydroxide (NaOH)
Hydrogen ions
Hydrogen atom that has a lot of electrons therefore bears a positive charge.
NaOH ----> Na+ + OH-
If sodium hydroxide is added to a beaker of water, the number of hydrogen ions decrease.
If the blood pH drops to about 7, acidosis results.
If the blood pH rises to about 7.8, alkalosis results.
HCl---> H+ + Cl-
If the hydrochloric acid is added to a beaker of water, the number of hydrogen ions (H+) increases greatly.
Explain the difference in H+ concentration between an acid and a base.
If theres more H+ then the its an acid, if theres an equal amount of H+ and OH- then the solution is neutral. If there are more OH- in the solution then it is basic.
Considering that manufacturing is essential to our national interests, how might we modify industrial processing to reduce sulfur dioxide and nitrogen oxide contamination?
If we came up with a cleaner way of manufacturing the things we need, then we could still manufacture without doing harm to the environment or people.
pH scale
Measurement scale for hydrogen ion concentration. Based on the formula -log[H+].
Some common acids from weakest to strongest.
Milk, root beer, urine, normal rain water, bread, black coffee, tomatoes, soda, bear, vinegar, lemon juice, stomach acid, hydrochloric acid (HCl)
Bases
Molecules tending to lower the hydrogen ion concentration in a solution and thus raise the pH numerically.
Acids
Molecules tending to raise the hydrogen ion concentration in a solution and thus it lowers its pH numerically.
Nature of Science
Our understanding of life continues to change over time as we uncover fundamental truths about chemistry. Items we use every day, including food, plastics, and medicine, are products of ongoing research in chemistry.
Evolution
Our understanding of life focuses on its interaction with water. Our search for waters on other planets underscores the central role that water plays in living matter.
Nature of Science
Scientific discoveries about chemistry, water, and carbon help us understand substances that are built from these atoms.
Connecting the Concepts with the Themes: Evolution
Six of the 92 naturally occurring elements-carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur--make up 95% of the body mass of organisms on Earth.
What acid rain trends are evident from the EPA data?
The burning of fossil fuels in factories, automobiles, and other industrial processes produces chemicals like SO2 and NOx that lead to acid deposition and destruction of the environment. Clean air legislation and stricter emission standards over the past several decades have resulted in steady decreases in SO2 and NOx, chemicals that lead to acid rain.
Explain the relationship between H+ or OH- concentration and pH
The more H+ added to a solution the more acidic it becomes, the more OH- you put into a solution the more basic it becomes.
Figure 2.13 The pH scale.
The pH scale ranges from 0 to 14, with 0 being the most acidic and 14 being the most basic. pH 7 (neutral pH) has equal amounts of hydrogen ions (H+) and hydroxide ions (OH-). An acidic pH has more H+ than OH- and a basic pH has more OH- than H+.
pH Scale: The pH scale is used to indicate the
acidity or basicity (alkalinity) of a solution. ^3
When hydrogen ions (H+) are
added to blood, the following reaction reduces acidity:
When hydroxide ions (OH-)
are added to blood, this reaction reduces basicity:
Many commercial products, such as shampoos or deodorants,
are buffered as an adde incentive for us to buy them.
Bases
are substances that either take up hydrogen ions (H+) or release hydroxide ions (OH-).
Figure 2B Trends in U.S. acid rain emissions. The burning of fossil fuels in factories,
automobiles, and other industrial processes produces chemicals like SO2 and NOx that lead to acid deposition and destruction of the environment.
The use of very tall smokestacks causes them to
be carried even hundreds of miles away. For example, acid rain in southeastern Canada results from the burning of fossil fuels in factories and power plants in the midwestern United States.
A pH above 7 is basic,
because the [OH-] is greater than the [H+].
A pH above 7 is an acidic solution,
because the hydrogen ion concentration is greater than the hydroxide concentration.
Buffers help keep the pH within normal limits
because they are chemicals or combinations of chemicals that take up excess hydrogen ions (H+) or hydroxide ions (OH-).
Acid rain may convert mercury in lake
bottom sediments to toxic methyl mercury.
Impact on Forests: The leaves of plants damaged by acid rain can no longer
carry on photosynthesis as before.
Acid rain in Canada and New England has
caused hundreds of lakes to be devoid of fish, and in some cases, any life at all.
Basic Solutions (Low H+ Concentration) Milk of magnesia and ammonia are
common basic solutions familiar to most people.
The pH scale was devised to eliminate the use of
cumbersome numbers. For example, the possible hydrogen ion concentrations of a solution are on the left of this listing and the pH is on the right: [H+] pH 0.000001 = 1 x 10^-6 6 0.0000001 = 1 x 10^-7 7 0.00000001 = 1 x 10^-8 8
Only a few water molecules at atom
dissociate, and the actual number of H+ and OH- is very small ( x 10^-7 moles/liter).^2
As we move up the scale from 0 to 14,
each unit is 10 times more basic than the previous unit.
To further illustrate the relationship between
hydrogen ion concentration and pH, consider the following question.
A number with a smaller negative exponent indicates a greater quantity of
hydrogen ions than one with a larger negative exponent. Therefore, pH 6 is an acidic solution.
Buffers are on of these
important mechanisms.
A pH of 7 represents a neutral state
in which the hydrogen ion and hydroxide ion concentrations are equal.
Buffers and pH: A buffer
is a chemical or a combination of chemicals that keeps pH within normal limits.
For example, hydrochloric acid (HCl)
is a strong acid that dissociates almost completely in this manner:
The pH of our blood when we are healthy
is always about 7.4--that is, just slightly basic (alkaline).
When water ionizes,
it releases an equal number of hydrogen ions (H+) (sometimes just called protons) and hydroxide ions (OH-)
Acid deposition includes rain or snow that has a pH of
less than 5, as well as dry acidic particles that fall to Earth from the atmosphere.
In New England and the southern Appalachians,
millions of acres of high elevation forests have been devastated.
For example, carbonic acid (H2CO3) is a weak acid that
minimally dissociates and then re-forms in the following manner:
Therefore, pH 5 is 100 times
more acidic than pH 7 and 100 times more basic than pH 3.
Impact on Lakes Acid rain adversely affects many aspects
of biological systems. Aluminum may leach from the solid of lakes, particularly in areas where the soil is thin and lack limestone (calcium carbonate, or CaCO3) as a buffer.
In humans, pH needs to be maintained within a narrow range,
or there are health consequences.
Determine how much more acidic a pH of 2.0 is than a pH of 4.0.
pH 2.0 is 100 times more acidic than pH 4.0.
In living organisms, the
pH of body fluids has to be maintained within a narrow range, or else molecules don't function correctly and our health suffers.
Clean air legislation and stricter emission
standards over the past several decades have resulted in steady decreases in SO2 and NOx, chemicals that lead to acid rain.
Sulfur dioxide and nitrogen oxides,
the main precursors of acid rain, have been steadily decreasing in the United States due to clean air legislation and strict emission limits.
The pH of blood is around 7.4, and blood is buffered in
the manner described next to keep the pH within a normal range.
Further, as we move down
the pH scale from pH 14 to pH 0, each unit is 10 times more acidic than the previous unit.
How might we prevent methyl mercury from entering biological systems and reduce the amount already present?
If we stopped using mercury and made an effort to clean rivers that are contaminated with mercury, this would help stop our waters from being contaminated.
For example, sodium hydroxide (NaOH) is
a strong base that dissociates almost completely in this manner:
Acidic Solutions (High H+ Concentrations) Lemon juice, vinegar, tomatoes,
and coffee are all acidic solutions.
Buildings and monuments made of limestone
and marble break down when exposed to acid rain.
Blood always contains a combination of some carbonic acid
and some bicarbonate ions.
When plants are under stress, they
become susceptible to diseases and pests of all types.
Normally, pH stability is possible because the
body has built-in mechanisms to prevent pH changes.
Over time, methyl mercury can accumulate in
body tissues and cause serious sensory and muscular health problems.
The acidity of a substance depends on
how fully it dissociates in water.
Both conditions can be life
threatening, so the blood pH must be kept around 7.4.
The Biological Systems feature,
"The impact of Acid Decomposition," describes detrimental environmental consequences of low pH rain and snow.
The pH scale ranges from
0 to 14.
Impact on Humans and Structures: Humans may be affected by acid rain.
Inhaling dry sulfate and nitrate particles appears to increase the occurrence of respiratory illnesses, such as asthma.
LOOK AT THE BOOK!
LOOK AT THE BOOK!
Distinguish between an acid and a base.
Acid is below 7 on the pH scale, base is above 7 on the pH scale. Acids consist of tea, soda, detergent. Bases consist of bleach, drain cleaner, toothpaste, and soap.
Evolution
Elements may be combined by chemical bonds to form the structures associated with life.
Biological Systems
Like all systems, chemistry consists of inputs and outputs, with resulting changes in energy.
Biological Systems
Many elements exist as ions in the body, and their functions depend on their charged nature.
Hydroxide ions
One of two ions that result when a water molecule dissociates; it has gained an electron and therefore bears a negative charge.
Which of the pH values listed indicates a higher hydrogen ion concentration
[H+] than pH 7, and therefore would be an acidic solution?