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Acids and Bases

Acids and Bases
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Dr.SamuelHunt,United Arab Emirates,Teacher
Published Date:21-07-2017
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Chapter 14 Acids and BasesTypes of Electrolytes • Salts are water-soluble ionic compounds. All strong electrolytes. +1 • Acids form H ions in water solution. +1 • Bases combine with H ions in water solution. -1 Increases the OH concentration. -1 +1 May either directly release OH or pull H off H O. 2 www.ThesisScientist.comProperties of Acids • Sour taste. • React with ―active‖ metals.  I.e., Al, Zn, Fe, but not Cu, Ag or Au. 2 Al + 6 HCl AlCl + 3 H 3 2  Corrosive. • React with carbonates, producing CO . 2  Marble, baking soda, chalk, limestone. CaCO + 2 HCl CaCl + CO + H O 3 2 2 2 • Change color of vegetable dyes.  Blue litmus turns red. • React with bases to form ionic salts. www.ThesisScientist.comCommon Acids Chemical name Formula Uses Strength Explosive, fertilizer, dye, glue Nitric acid HNO Strong 3 Explosive, fertilizer, dye, glue, Sulfuric acid H SO Strong 2 4 batteries Metal cleaning, food prep, ore Hydrochloric acid HCl Strong refining, stomach acid Fertilizer, plastics and rubber, Phosphoric acid H PO Moderate 3 4 food preservation Plastics and rubber, food Acetic acid HC H O Weak 2 3 2 preservation, vinegar Metal cleaning, glass etching Hydrofluoric acid HF Weak Soda water Carbonic acid H CO Weak 2 3 Eye wash Boric acid H BO Weak 3 3 www.ThesisScientist.comStructures of Acids • Binary acids have acid hydrogens attached to a nonmetal atom. HCl, HF Hydrofluoric acid www.ThesisScientist.comStructure of Acids • Oxyacids have acid hydrogens attached to an oxygen atom. H SO , HNO 2 4 3 www.ThesisScientist.comStructure of Acids • Carboxylic acids have COOH group.  HC H O , H C H O 2 3 2 3 6 5 3 • Only the first H in the formula is acidic.  The H is on the COOH. www.ThesisScientist.comProperties of Bases • Also known as alkalis. • Taste bitter.  Alkaloids = Plant product that is alkaline. Often poisonous. • Solutions feel slippery. • Change color of vegetable dyes.  Different color than acid.  Red litmus turns blue. • React with acids to form ionic salts.  Neutralization. www.ThesisScientist.comCommon Bases Chemical Common Formula Uses Strength name name Sodium Lye, Soap, plastic, NaOH Strong hydroxide caustic soda petrol refining Potassium Caustic Soap, cotton, KOH Strong hydroxide potash electroplating Calcium Ca(OH) Slaked lime Cement Strong 2 hydroxide Sodium NaHCO Baking soda Cooking, antacid Weak 3 bicarbonate Magnesium Milk of Mg(OH) Antacid Weak 2 hydroxide magnesia Detergent, Ammonium NH OH, Ammonia 4 fertilizer, Weak hydroxide NH (aq) water 3 explosives, fibers www.ThesisScientist.comStructure of Bases • Most ionic bases contain OH ions.  NaOH, Ca(OH) 2 2- • Some contain CO ions. 3  CaCO NaHCO 3 3 • Molecular bases contain structures that react with + H .  Mostly amine groups. www.ThesisScientist.comArrhenius Theory - • Bases dissociate in water to produce OH ions and cations.  Ionic substances dissociate in water. + – NaOH(aq) → Na (aq) + OH (aq) + • Acids ionize in water to produce H ions and anions.  Because molecular acids are not made of ions, they cannot dissociate.  They must be pulled apart, or ionized, by the water. + – HCl(aq) → H (aq) + Cl (aq)  In formula, ionizable H is written in front. + – HC H O (aq) → H (aq) + C H O (aq) 2 3 2 2 3 2 www.ThesisScientist.comArrow Conventions • Chemists commonly use two kinds of arrows in reactions to indicate the degree of completion of the reactions. • A single arrow indicates that all the reactant molecules are converted to product molecules at the end. • A double arrow indicates that the reaction stops when only some of the reactant molecules have been converted into products.  in these notes. www.ThesisScientist.comArrhenius Theory, Continued HCl ionizes in water, NaOH dissociates in water, + – + – producing H and Cl ions. producing Na and OH ions. www.ThesisScientist.comBrønsted–Lowry Theory • A Brønsted-Lowry acid–base reaction is any + reaction in which an H is transferred.  Does not have to take place in aqueous solution.  Broader definition than Arrhenius. + + • Acid is H donor; base is H acceptor. +  Since H is a proton, acid is a proton donor and base is a proton acceptor.  Base structure must contain an atom with an + unshared pair of electrons to bond to H . + • In the reaction, the acid molecule gives an H to the base molecule. – + H–A + :B  :A + H–B www.ThesisScientist.comComparing Arrhenius Theory and Brønsted–Lowry Theory • Brønsted–Lowry theory • Arrhenius theory HCl(aq) + H O(l)  HCl(aq)  2 − + + − Cl (aq) + H O (aq) H (aq) + Cl (aq) 3 HF(aq) + H O(l)  HF(aq)  2 + − − + H (aq) + F (aq) F (aq) + H O (aq) 3 NaOH(aq)  NaOH(aq) + H O(l)  2 + − + − Na (aq) + OH (aq) Na (aq) + OH (aq) + H O(l) 2 NH OH(aq)  NH (aq) + H O(l)  4 3 2 + − + − NH (aq) + OH (aq) NH (aq) + OH (aq) 4 4 www.ThesisScientist.comAmphoteric Substances • Amphoteric substances can act as either an acid or a base.  They have both transferable H and an atom with a lone pair. + • HCl(aq) is acidic because HCl transfers an H to + H O, forming H O ions. 2 3 +  Water acts as base, accepting H . – + HCl(aq) + H O(l) → Cl (aq) + H O (aq) 2 3 + • NH (aq) is basic because NH accepts an H from 3 3 – H O, forming OH (aq). 2 +  Water acts as acid, donating H . + – NH (aq) + H O(l)  NH (aq) + OH (aq) 3 2 4 www.ThesisScientist.comConjugate Pairs • In a Brønsted-Lowry acid-base reaction, the original base becomes an acid in the reverse reaction, and the original acid becomes a base in the reverse process. • Each reactant and the product it becomes is called a conjugate pair. • The original base becomes the conjugate acid; the original acid becomes the conjugate base. www.ThesisScientist.comExample—Identify the Brønsted–Lowry Acids and Bases and Their Conjugates in the Reaction. – + H SO + H O HSO + H O 2 4 2 4 3  + When the H SO becomes HSO , it loses an H , so 2 4 4  H SO must be the acid and HSO its conjugate base. 2 4 4 + + When the H O becomes H O , it accepts an H , so 2 3 + H O must be the base and H O its conjugate acid. 2 3 – + H SO + H O HSO + H O 2 4 2 4 3 Acid Base Conjugate Conjugate base acid www.ThesisScientist.comExample—Identify the Brønsted-Lowry Acids and Bases and Their Conjugates in the Reaction, Continued. – – HCO + H O H CO + HO 3 2 2 3 +  When the HCO becomes H CO , it accepts an H , so 3 2 3  HCO must be the base and H CO its conjugate acid. 3 2 3  + When the H O becomes OH , it donates an H , so 2  H O must be the acid and OH its conjugate base. 2 – – HCO + H O H CO + HO 3 2 2 3 Base Acid Conjugate Conjugate acid base www.ThesisScientist.comPractice—Write the Formula for the Conjugate Acid of the Following: + •H O H O 2 3 + •NH NH 3 4 2− − •CO HCO 3 3 1− •H PO H PO 2 4 3 4 www.ThesisScientist.com