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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_scale
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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?ion
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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?ion
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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?ion
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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