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Chapter 5 Acids, Bases & Body Chemistry Chemistry in Society
Review Terms: homogeneous mixtures, solutions, solvent, and solute
Chemical reactions are very important in chemistry-one very common one is called acid-base reactions. In acid base reactions most of the reactions are in water or aqueous
solutions: where water is the solvent. Therefore aqueous solutions are water solutions.
Solute particle may be ions or molecules
Ionic solutions (Electrolytes)-conduct electricity
Molecular solutions (Non-electrolytes)-do not conduct electricity
Ionic dissociation-the separation of ions of a solute when the substance is dissolved.
e.g. sodium chloride dissolving in water NaCl Na+(aq) + Cl-(aq)
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Ionization-when a molecular solute dissolves in water to produce ions. E.g. HCl is
composed of covalent diatomic molecules. Therefore produce ions when dissolved in
water. HCl H+(aq) + Cl-(aq)
Note: The proton (H+) in aqueous solution does not exist independently, but becomes
attach to the negative end of a water molecule. The proton in water is said to behydrated and referred to as the hydronium ion, H3O
+.
Diagram of hydronium ion
Questions
(1) What is an acid? A base?
(2) What would happen if I put a flower into an acidic solution? a basic solution?
(3) How can you tell if a solution is acidic or basic?
(4) How do acidic solutions vary? basic solutions?
(5) Are acids poisonous? bases?
Acids and Bases are of great significance in everyday life
Baking soda and powder are weak bases vital to cooking
Lye (NaOH) is a strong base often used in oven cleaners
Lime (
CaO) is a base used to decrease the acidity in soil
Antacids contain bases to neutralize excess acidity in the stomach
Acid skin tends to produce pimples
Radiators corrode when antifreeze acidifies
Organic acids, which are commonly found in foods and animals.
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Acids andbasesare a way of classifying compounds based upon what happens to themwhen you place them in water.
What is and acid?
Background
Water will naturally "break up" into H+ and OH- in a process known as dissociation.When water dissociates the hydrogen atom breaks its bond with oxygen and leaves
behind its electron. The hydrogen atom is now positively charged and properly called a
hydrogen ion. The remaining hydrogen is still connected to the oxygen, which now has
an extra electron, giving this pair a negative charge. The OH- molecule is properly calleda hydroxide ion. The amount of dissociated water molecules in relation to all the water
molecules is very small, and since the overall amounts of H+ and OH- are equal, they
cancel each other out.
If, for some reason, the H+ and OH- are not balanced, an acid or base is formed. The
extent to which a compound is acidic or basic is measured by thepH scale. On the scale,
numbers range from 0 (most acidic) to 14 (most basic). Pure water has a pH of 7, whichis neutral.
It is important to note that this scale is logarithmic. Thus, a pH of 2 is not twice as acidic
as a 4, but rather 100 times as acidic. That same pH of 2 is not three times as acidic as a
pH of 6, but rather 10,000 times as acidic.
pH = - log[H+]. Defined as the negative log (exponent of ten) of the proton concentration
expressed as [H+]/H3O+]. Thus, when pH has low values, the concentration of hydrogen
ions is high.
http://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ph_scalehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ph_scale8/14/2019 what chemistry is all about
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ACIDS
Aqueous solutions that have more H+ than OH-. Acidsare substances that, whendissolved in water, split into two ions, one of which is an H+ion (The H indicates that the
ion is hydrogen, and the + indicates that it is positively charged, meaning that there is no
electron.). A well known acid is HCl (hydrochloric acid), which splits into two ions whenplaced in water: H+ and Cl-.
Two definitions can be used for this class:
1. Arrhenius Definition: a substance that releases hydrogen (H+)/ hydronium ion
(H3O+) when dissolved in water. E.g. HCl, H2SO4, HNO3, H3PO4, CH3COOH
2. Brnsted Lowry Definition: A proton donor (H+)
NH4+ + H2O NH3 + H3O
+ OR NH4+ NH3 + H
+
Properties of Acids
Acids are characterized by
Theirsour taste. Many of the foods you eat, such as oranges, green apples, and
rhubarb, taste sour due to the acids which they form.
Their ability to react with (dissolve) active metals e.g Fe, Sn, Zn, Mg to produce
hydrogen gas. Zn + 2HCl ZnCl2 + H2(g). Many cleaners have acids in them. Itis important that you read the warning labels on your household cleaners as we do
not advise that you use acidic solutions to clean water pipes in your home.
Their ability to turn indicator dye litmus from blue to red.
Their ability to neutralizebases.
Acids can either be strong or weak
http://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?electronhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?electronhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ion8/14/2019 what chemistry is all about
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The cleaners used to unclog sinks (e.g. Draino, Liquid Plumber) are strong bases that
readily dissolve hair and grease, but leave the pipes unscathed.
Bases can either be strong or weak
Strong bases- completely dissociated in water
NaOH Na+ + OH-
Weak bases- remain mostly in molecular form when dissolved in water e.g.ammonia.
NH3 + H2O
NH4+
+ OH
-
Common Acids & Bases:
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Metal Oxides-Basic Anhydrides
React with water to form bases:
CaO2 + H2O Ca(OH)2 +
Neutralization
When acids react with bases the properties of both species disappear. If you put both anacidandabase into the same container of water, they tend to cancel out the effects of one
another. For example, if both HCl and NaOH are placed in water, the Na+ and Cl-ions
combine to form NaCl (table salt), and the H+ and OH- ions combine to form H2O(water).
NaOH + HCl NaCl + H2O
Salt: A compound composed of the positive ion of a base and the negative ion of an acid.
Indicators-Measuring the pH
There are substances, which have the property of changing their color when they come incontact with an acidic or basic environment. These substances are called pH indicators.
A dye whose colour depends on its pH e.g. litmus. Indicators change colour within a
certain pH range, and the range of pH value within which the colour change take place
depends on the particular indicator. Indicators measure [H+]/ [OH-] without affecting it.
http://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?acidhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?basehttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ion8/14/2019 what chemistry is all about
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IndicatorColor change
interval (pH)Acid Base
thymol blue 1.2 - 2.8 red yellow
methyl orange 3.1 - 4.4 red yellow
methyl red 4.4 - 6.2 red yellowchlorophenol red 5.4 - 6.8 yellow red
bromothymol blue 6.2 -7.6 yellow blue
phenol Red 6.4 - 8.0 yellow red
thymol Blue 8.0 - 9.6 yellow blue
Phenolphthalein 8.0 - 10.0 colorless red
Alizarin yellow 10.0 -12.0 yellow green
Antacids
Antacids work by neutralizing acid and coating the stomach
Basic compounds used to dissolve the amount of acid (HCl) in the stomach.
Antacids are used to relieve the uncomfortable symptoms of acid indigestion,heartburn, gas, and sour stomach.
Side effects may include:
Chalky taste, constipation, diarrhea, increased thirst, stomach cramps
Buffers
Buffers arecompounds that tend to neutralize the pH of a solution by combining witheitherH+ions or OH- ions to keep the solution neutral.Buffersplay a very important
role in mostorganisms, as many organismscannot live at pHs that are too acidic or too
basic. This is because certain reactions, which occur in organisms, are hindered by theeffects of an excess of charged ionsin the environment.
http://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?compoundhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ionhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?bufferhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?organismhttp://library.thinkquest.org/27819/cgi-bin/glossary.cgi?ion8/14/2019 what chemistry is all about
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Buffers resist changes to pH on addition of small amounts of acid or base. Common
buffer mixtures are composed of both a weak acid and its salt eg. ethanoic acid and
sodium ethanoate or a weak base and its salt eg. ammonia and ammonium sulphate.In the buffer made from ethanoic acid and sodium ethanoate, two equilibria exist;
CH3CO2H (aq) + H2O (l) H3O+ (aq)+ CH3CO2
-(aq)
CH3CO2Na CH3CO2-+ Na+
Adding a small amount of acid to equilibrium 1, will make it shift to the left hand side, to
reduce the hydrogen ion concentration and therefore the pH will not change. This will
also reduce the concentration of CH3CO2- ions, but there is a large concentration of these
present from equation 2. Adding a small amount of OH- ions will remove hydrogen ions
to make water, and cause the equilibrium to shift to the right.The equilibrium in the second equation lies far to the right. This keeps the concentration
of CH3CO2- constant.
The Carbonic-Acid-Bicarbonate Buffer in the Blood
By far the most important buffer for maintaining acid-base balance in the blood is the
carbonic-acid-bicarbonate buffer. The simultaneous equilibrium reactions of interest are
Calculating the pH of a Buffer
The following formula is used:
pH = pKa -log[acid] /[salt]
How Buffers Work: A Quantitative View
The kidneys and the lungs work together to help maintain a blood pH of 7.4 by affecting
the components of the buffers in the blood. Therefore, to understand how these organs
help control the pH of the blood, we must first discuss how buffers work in solution.
Acid-base buffers confer resistance to a change in the pH of a solution when hydrogenions (protons) or hydroxide ions are added or removed. An acid-base buffer typically
consists of a weak acid, and its conjugate base (salt). Buffers work because theconcentrations of the weak acid and its salt are large compared to the amount of protons
or hydroxide ions added or removed. When protons are added to the solution from an
external source, some of the base component of the buffer is converted to the weak-acid
component (thus using up most of the protons added); when hydroxide ions are added tothe solution (or, equivalently, protons are removed from the solution; protons are
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dissociated from some of the weak-acid molecules of the buffer, converting them to the
base of the buffer (and thus replenishing most of the protons removed). However, the
change in acid and base concentrations is small relative to the amounts of these speciespresent in solution. Hence, the ratio of acid to base changes only slightly. Thus, the effect
on the pH of the solution is small, within certain limitations on the amount of H+ or OH-
added or removed.
The Carbonic-Acid-Bicarbonate Buffer in the Blood
By far the most important buffer for maintaining acid-base balance in the blood is the
carbonic-acid-bicarbonate buffer.
Many people today are interested in exercise as a way of improving their health andphysical abilities. But there is also concern that too much exercise, or exercise that is not
appropriate for certain individuals, may actually do more harm than good. Exercise has
many short-term (acute) and long-term effects that the body must be capable of handlingfor the exercise to be beneficial.
When we exercise, our heart rate, systolic blood pressure, and cardiac output (the amount
of blood pumped per heart beat) all increase. Blood flow to the heart, the muscles, and
the skin increase. The body's metabolism becomes more active, producing CO2 and H+ in
the muscles. We breathe faster and deeper to supply the oxygen required by this increased
metabolism. Eventually, with strenuous exercise, our body's metabolism exceeds the
oxygen supply and begins to use alternate biochemical processes that do not require
oxygen. These processes generate lactic acid, which enters the blood stream. As wedevelop a long-term habit of exercise, our cardiac output and lung capacity increase, even
when we are at rest, so that we can exercise longer and harder than before. Over time, theamount of muscle in the body increases, and fat is burned as its energy is needed to helpfuel the body's increased metabolism.
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Acidosis is a condition caused by removal of bicarbonate or an increase in carbonic acid
in blood. The net result is a disturbance in the carbonic acid-bicarbonate equilibrium toproduce an excess [H+] in blood causing lower blood pH. Metabolic acidosis can occur
as a result of diabetes, starvation and high fat diet all of which leads to the production of
ketones in the blood. Ketones bind & remove bicarbonate. If not controlled it can be fatal.
Alkalosis occurs when [bicarbonate] increases forcing the equilibrium to remove protons
from blood causing blood pH to rise. So pH becomes alkaline leading to vomiting,
nausea, and headache.
Temporary metabolic alkalosis occurs when there is an intake of sodium bicarbonate e.g.if large a mounts are taken for acid in the stomach. Respiratory alkalosis can be induced
by hyperventilation i.e. excessive exhalation of carbon dioxide from lungs too quickly
causing too great a loss of H+ from the large reservoir. Anything that causes sustained
rapid breathing can induce temporary alkalosis, e.g. hysteria (pop concert), hot baths,training.
Athletes such as marathon runners learn to control breathing so as to minimize alkalosis.
Sprinters and swimmers who understand biochemistry tune their bodies for maximum
effort. Strenuous bursts of muscle activity produce high levels of lactic acid as glucose isbroken down for energy. Lactic acid can lower the pH of blood and cause muscle
cramp/fatigue.
To counteract this, athletes will prepare by rapid deep breathing for 30-40 seconds beforethe race to hyperventilate and introduce temporary alkaline conditions that will help to
neutralize the acidity arising from lactic acid.
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Other important buffers in the body are the H3PO4, amino acid buffer systems
Acid rain: refer to handout