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Chapter 13

CH. 13 ACIDS AND BASES.docx

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Department
Chemistry
Course Code
CHEM 1100
Professor
Kim Bolton

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CH. 13 ACIDS AND BASES • Acid a substance that produces hydrogen ions (H+) ions • Base a substance that produces hydroxide ions (OH-) in solution Properties of Acids: Tasting Sour and Dissolving Metals Properties of acids: 1. Acids dissolve many metals 2. Sourness in foods is caused by acids, molecules that release protons  These protons or hydrogen ion (H+) react with protein molecules on the tongue  The reaction causes the protein molecule to change its shape sending an impulse to the brain that we interpret as sour  The more acidic the food, the more sour the taste 3. Reacts with bases to form water and a salt through neutralization reactions 4. Turns litmus paper red Common Laboratory Acids Name Formula Uses Hydrochloric HCl Cleaning of metals, preparation of foods, refining of ores acid Sulfuric acid H 2O 4 Manufacture of fertilizers, explosives, dyes and glues Nitric acid HNO 3 Manufactures of fertilizers, explosives, and dyes Phosphoric acid H 3O 4 Manufacture of fertilizers and detergents; flavour additive for food and drinks Acetic acid CH 3OO Present in vinegar; used in manufacture of plastics and rubber; H used as preservation in foods and as solvent for resins and oils • In concentrated forms many acids are dangerous  Spilled on clothing dissolve clothing material  Contact skin produce severe burns  Ingested will damage mouth, throat, stomach, and gastrointestinal tract  Large amounts can kill Properties of Bases: Tasting bitter and Feeling Slippery 1. Bases feel slippery on the skin 2. Bases have bitter taste 3. React with acids to form water and salt CH. 13 ACIDS AND BASES 4. Bases turn litmus paper blue Common Laboratory Bases Name Formul Uses a Sodium hydroxide NaOH Neutralization of acids, petroleum processing, and manufacture of soap and plastics Potassium KOH Manufacture of soap and paint remover; cotton processing; hydroxide electroplating Sodium NaHCO Antacid, source of CO2, in fire extinguishers and cleaning bicarbonate 3 products Ammonia NH 3 Detergent; removing stains; extracting plant colours; manufacture of fertilizers, explosives, and synthetic fibers • In concentrated forms many bases are dangerous and will burn the skin on contact and if ingested will damage the mouth, throat, and gastrointestinal tract Writing Neutralization Equations Acid + Base  water + salt Acids and Bases: molecular definitions • Svante Arrhenius  Arrhenius definition of acids and bases: Arrhenius acid substance that produces hydrogen ions (H+) in solution Arrhenius base substance that produces hydroxide ions (OH-) in solution *Does not apply in all cases – ex. Ammonia (NH3) is a base* • The Bronsted-Lowry definition of acids and bases focuses on the transfer of H+ ions (protons) Bronsted-Lowry acid proton donor Bronsted-Lowry base proton acceptor Strong and Weak Acids and Bases • Strong acid an acid that completely dissociates in solution (ex. HCl, HNO ,3H S2 ) 4 • Weak acid an acid that does not completely dissociate in solution (ex. CH C3OH, HCOOH, C H C6O5, C H O(CO3H5 ) 3 • Strong base a base that completely dissociates in solution (NaOH) • Weak base a base that does not completely dissociate in solution (NH , 3 H 2H 5 2 C 5 N5 C H6N5 ) 2 CH. 13 ACIDS AND BASES Specifying the Concentration of Acids and Bases: The pH Scale + • The acidity of a solution is normally specified by the concentration of H O 3n moles per liter (M) + • The concentration of H O3in an acid solution will not necessarily be equal to the concentration of the acid itself; it depends on whether the acid is strong or weak • [H3O +] = concentration of H 3 in M • Pure water at 25˚C naturally contains [H O 3 = 1 X 10 M (0.0000001 M), due to slight acid-base behaviour in water itself: −¿ +¿+O H ¿ ¿ H 2+H O⇌ 2 O 3 + - • A solution is considered acidic if it has [H3O ] ˃ 1 X 10 7M • The greater the [H O3], the more acidic the solution • A solution is considered basic if it has an [H 3 ] ˂ 1 X 10 -7 • The pH scale expresses the acidity or basicity of a solution • A solution with a pH of 7 is neutral, a pH lower than 7 is acidic, and a pH greater than 7 is basic • For every change of one unit on the pH scale, the [H O ]3concentration changes by a factor of 10 + Relationship Between pH and H O Co3centration [H ] pH Example 1.00 0 HCl (1 M) 1.00 X 10 1 Stomach Acid -2 1.00 X 10 2 Lemon Juice -3 Acids 1.00 X 10 3 Vinegar, Apples 1.00 X 10 -4 4 Soda, Beer CH. 13 ACIDS AND BASES -5 1.00 X 10 5 Rainwater -6 1.00 X 10 6 Milk -7 Neutral 1.00 X 10 7 Pure water -8 1.00 X 10 8 Egg whites -9 1.00 X 10 9 Baking Soda Solution -10 1.00 X 10 10 Milk of Magnesia Bases -11 1.00 X 10 11 Ammonia -12 1.00 X 10 12 Mineral Lime Solution 1.00 X 10 -13 13 Liquid Drano 1.00 X 10 -14 14 NaOH (1 M) Some Common Acids • Citric acid (lemons, limes, oranges, grapefruit) are sour, and resistant to spoilage because many microorganisms cannot survive in low pH environment • Many low acid foods can be made spoiled resistant by storing them in acid or by fermentation with lactic-acid forming bacteria (pickling preserves
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