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ACIDS, BASES & SALTS
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The Arrhenius Theory of Acids and Bases
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Arrhenius Theory of Acids and Bases: an acid contains hydrogen and ionizes in solutions to produce H + ions: HCl H + (aq) + Cl - (aq)
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Arrhenius Theory of Acids and Bases: a base contains an OH - group and ionizes in solutions to produce OH - ions: NaOH Na + (aq) + OH - (aq)
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Neutralization Neutralization: the combination of H + with OH - to form water. H + (aq) + OH - (aq) H 2 O (l) Hydrogen ions (H + ) in solution form hydronium ions (H 3 O + )
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In Reality… H + + H 2 O H 3 O + Hydronium Ion (Can be used interchangeably with H + )
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Commentary on Arrhenius Theory… One problem with the Arrhenius theory is that it’s not comprehensive enough. Some compounds act like acids and bases that don’t fit the standard definition.
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Bronsted-Lowry Theory of Acids & Bases
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Bronsted-Lowry Theory of Acids & Bases: An acid is a proton (H + ) donor A base is a proton (H + ) acceptor
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for example… HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl - (aq) Proton transfer Acid Base
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NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) BASE ACID CONJUGATE ACID CONJUGATE BASE Ammonia is a proton acceptor, and thus a base another example… Water is a proton donor, and thus an acid.
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Conjugate acid-base pairs Conjugate acid-base pairs differ by one proton (H + ) A conjugate acid is the particle formed when a base gains a proton. A conjugate base is the particle that remains when an acid gives off a proton.
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Examples: In the following reactions, label the conjugate acid-base pairs: H 3 PO 4 + NO 2 - HNO 2 + H 2 PO 4 - CN - + HCO 3 - HCN + CO 3 2- HCN + SO 3 2- HSO 3 - + CN - H 2 O + HF F - + H 3 O + acidbasec. acidc. base acidbasec. acidc. base acid base c. acid c. base acidbase c. acidc. base
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Amphoteric Substances A substance that can act as both an acid and a base (depending on what it is reacting with) is termed amphoteric. Water is a prime example.
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Properties of Acids and Bases ACIDS Have a sour taste Change the color of many indicators Are corrosive (react with metals) Neutralize bases Conduct an electric current BASES Have a bitter taste Change the color of many indicators Have a slippery feeling Neutralize acids Conduct an electric current
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Other Household Acids and Bases Antacid: a weak base that neutralizes excess stomach acid. The pH of shampoo is generally kept between 5 and 8. Lemon juice is an acid that is sometimes used to help keep fruit looking fresh. What will happen to left apple?
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Indicators- “Way Cool” Cyber-lab: http://www.miamisci.org/ph/phlemon.ht ml
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Strength of Acids and Bases A strong acid dissociates completely in sol’n: HCl H + (aq) + Cl - (aq) A weak acid dissociates only partly in sol’n: HNO 2 H + (aq) + NO 2 - (aq) A strong base dissociates completely in sol’n: NaOH Na + (aq) + OH - (aq) A weak base dissociates only partly in sol’n: NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq)
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The Lewis Theory of Acids and Bases
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The Lewis Theory of Acids & Bases Lewis acid: a substance that can accept an electron pair to form a covalent bond (electron pair acceptor). Lewis base: a substance that can donate an electron pair to form a covalent bond (electron pair donor).
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Neutralization Neutralization: the formation of a coordinate covalent bond in which both electrons originated on the same (donor) atom.
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Example 1: Ionization of NH 3 : NH 3 + H 2 O NH 4 + + OH - N N H H H OHH+ H H H HH + O.. + - acid base
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Example 2: Auto-ionization of water: H 2 O + H 2 O H 3 O + + OH - O O HH OHH+ H HHH + O.. + - acid base..
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Example 3: Reaction of NH 3 with HBr (a Lewis AND a Bronsted-Lowry acid-base reaction): NH 3 + HBr NH 4 + + Br - N N H H H BrH+ H H H H +.. + - acid base
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Acid Base Theories Lewis Bronsted-Lowry Arrhenius
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SUMMARY OF ACID-BASE THEORIES TheoryAcid DefinitionBase Definition Arrhenius Theory Any substance which releases H + ions in water solution. Any substance which releases OH - ions in water solution Brǿnsted- Lowry Theory Any substance which donates a proton. Any substance which accepts a proton. Lewis Theory Any substance which can accept an electron pair. Any substance which can donate an electron pair.
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Acid-Base Reactions Neutralization reactions: reactions between acids and metal hydroxide bases which produce a salt and water. H + ions and OH - ions combine to form water molecules: H + (aq) + OH - (aq) H 2 O (l)
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Example 1: the reaction of HCl and NaOH (there are 3 ways to write the chemical equation): Balanced formula unit equation: HCl (aq) + NaOH (aq) H 2 O (l) + NaCl (aq) Total ionic equation: H + (aq) +Cl - (aq) +Na + (aq) +OH - (aq) H 2 O (l) +Na + (aq) +Cl - (aq) Net ionic equation: H + (aq) + OH - (aq) H 2 O (l)
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Example 2: Write the 3 types of equations for the reaction of hydrobromic acid, HBr, with potassium hydroxide, KOH. Balanced formula unit equation: HBr (aq) + KOH (aq) H 2 O (l) + KBr (aq) Total ionic equation: H + (aq) +Br - (aq) +K + (aq) +OH - (aq) H 2 O (l) +K + (aq) +Br - (aq) Net ionic equation: H + (aq) + OH - (aq) H 2 O (l)
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Example 3: Write the 3 types of equations for the reaction of nitric acid, HNO 3, with calcium hydroxide, Ca(OH) 2. Balanced formula unit equation: 2HNO 3 (aq) + Ca(OH) 2 (aq) 2H 2 O (l) + Ca(NO 3 ) 2 (aq) Total ionic equation: 2H + (aq) +2NO 3 - (aq) +Ca 2+ (aq) +2OH - (aq) 2H 2 O (l) +Ca 2+ +2NO 3 - (aq) Net ionic equation: H + (aq) + OH - (aq) H 2 O (l)
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