acids and bases - al akhawayn universitys.elhajjaji/chap7_1400_sum2010.pdf · 7/23 buffers and...
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Chapter 7Chapter 7
Acids and Bases
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Acids and Bases: Experimental
DefinitionsAcids:
• Taste sour.
• Turn litmus red.
• React with active metals to release hydrogen gas.
• React with bases to form water and a salt.
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Acids and Bases: Experimental
Definitions Bases:
• Taste bitter.
• Turn litmus blue.
• Feel slippery.
• React with acids to form water and a salt.
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Acids and Bases: Experimental
Definitions
acids bases salts
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Acids, Bases, and Salts
Arrhenius Theory
Acid: A molecular substance that ionizes in aqueous solution to form hydrogen ions (H+).
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Acids, Bases, and Salts
Arrhenius Theory
Base: A substance that produces hydroxide ions (OH-) in aqueous solution.
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Acids, Bases, and Salts
Neutralization: When an acid reacts with a base, the properties of each are neutralized and the products are water and a salt.
Acid + Base → Water + Salt
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Acids, Bases, and Salts
Limitations of the Arrhenius Theory
• H+ ions do not exist in water solution. Protons react with water to form hydronium ions (H3O
+).
H+ + H2O → H3O+
• The Arrhenius theory does not explain the basicity of ammonia and similar compounds.
• It only applies to reactions in aqueous solution.
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Acids, Bases, and Salts
Brønsted-Lowry Theory
Acid: Proton donor
HA + H2O → H3O+ + A-
Base: Proton acceptor
NH3 + H2O → NH4+ + OH-
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Acids, Bases, and Salts
Brønsted-Lowry Theory
HA + H2O → H3O+ + A-
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Acidic and Basic Anhydrides
Anhydride means without water.
Nonmetal oxides are acidic anhydrides.
SO3 + H2O → H2SO4
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Acidic and Basic Anhydrides
Metal oxides are basic anhydrides.
Example:
Lime (calcium oxide) reacts with water to form slaked lime (calcium hydroxide).
CaO + H2O → Ca(OH)2
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Strong and Weak Acids and
BasesStrong acids ionize completely in water solution.
HCl(aq) → H+(aq) + Cl-(aq)
Weak acids only partially ionize in water solution.
HCN(aq) ↔ H+(aq) + CN-(aq)
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Strong and Weak Acids and
Bases
Strong bases ionize completely in water solution.
NaOH(aq) → Na+(aq) + OH-(aq)
Weak bases only partially ionize in water solution.
NH3(aq) + H2O ↔ NH4+(aq) + OH-(aq)
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Strong and Weak Acids and
Bases
Ammonia accepts a proton from water, forming a basic solution.
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Neutralization
The reaction of an acid with a base is called neutralization. Water molecules are the result of the reaction between hydrogen ions and hydroxide ions.
H+ + OH- ↔ H2O
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Neutralization
During neutralization, an acid reacts with a base, forming water and a salt.
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Neutralization
The amount of acid (or base) in a solution is determined by careful neutralization.
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The pH Scale
pH is a means of expressing the acidity or basicity of a solution.
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The pH Scale
pH means “power” of hydrogen.
pH = -log[H+]
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The pH Scale
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Buffers and Conjugate Acid-
Base PairsConjugate acid-base pairs are compounds or ions that differ by one proton (H+).
For example, the chloride ion (Cl-) is the conjugate base of the acid, hydrochloric acid (HCl).
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Buffers and Conjugate Acid-
Base Pairs
Buffer solutions contain a weak acid and its conjugate base. Such solutions are capable of maintaining a nearly constant pH when small amounts of acid or base are added.
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Acid Rain
Nonmetal oxides present in air react with water,
forming acidic solutions. Rain with a pH of less than 5.6 is considered to be acid rain. Carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen monoxide (NO), and nitrogen dioxide (NO2) are the major nonmetallic oxides responsible for acid rain formation.
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Antacids: A Basic Remedy
Hyperacidity is when the stomach secretes too much acid. Antacids are often taken to neutralize excess acid and reduce the symptoms of hyperacidity.
Excessive use of antacids can lead to an increase in the pH of blood, a condition known as alkalosis.
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Antacids: A Basic Remedy
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Antacids: A Basic Remedy
Substance Formula Product(s)
Sodium bicarbonate
NaHCO3 Baking soda
Calcium carbonate
CaCO3 Tums®
Aluminum hydroxide
Al(OH)3 Amphojel®
Magnesium hydroxide
Mg(OH)2 Milk of Magnesia®
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Acids and Bases in Industry and
at HomeSulfuric acid is the leading chemical substance produced in the U.S. It is used to manufacture fertilizers and industrial chemicals. It is the acid of automotive batteries. Production is 40 billion kg/year.
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Acids and Bases in Industry and
at Home
Hydrochloric acid has a number of uses. It is used as a rust remover, and it removes lime from mortar and household plumbing fixtures. It can be purchased from hardware stores as muriatic acid. Annual U.S. production is 4 billion kg.
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Acids and Bases in Industry and
at Home
Lime (CaO) is produced by heating limestone (CaCO3).
CaCO3 + heat → CaO + CO2
Lime can be slaked by reacting with water to make calcium hydroxide (Ca(OH)2). Slaked lime is used to make mortar and cement and to sweeten soil. Annual U.S. production is 22 billion kg.
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Acids and Bases in Industry and
at Home
Soil can be
“sweetened” by adding slaked lime [Ca(OH)2].
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Acids and Bases in Industry and
at Home
Sodium hydroxide, also known as lye, can be
purchased for home use as oven cleaner or drain cleaners. It is used commercially to make soap. Annual U.S. production is 9 billion kg.
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Acids and Bases in Industry
and at Home
Ammonia is produced for use as fertilizer and in
household cleaning products. Production is about 11 billion kg/year.
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Acids and Bases in Health and
DiseaseConcentrated acids and bases are corrosive to
tissue and are health hazards. They can denature proteins in living cells.
The human body has wonderful mechanisms for maintaining the proper pH of tissue, blood, and body fluids.