14_acids_and_bases - Chapter Chapter 14 Acids and Bases...

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hapter 14 Chapter 14 Acids and Bases
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Properties of Acids and Bases
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Svante Arrhenius (1859-1927) First to develop a theory for cids and bases in aqueous acids and bases in aqueous solution
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rrhenius Acids Arrhenius Acids Compounds which dissolve (dissociate) in water to produce H + ions xamples: Examples: HCl(aq) H + (aq) + Cl - (aq) H SO (aq) 2H + (aq) + SO 2- (aq) 2 4 4 Arrhenius Bases Ionic compounds which dissolve (dissociate) in water to produce OH - ions xamples: Examples: NaOH(aq) Na + (aq) + OH - (aq) Ca(OH) (aq) Ca 2+ (aq) + 2OH - (aq) () 2 ( q) ( q) ( q)
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Arrhenius acids react with Arrhenius bases to form a neutral salt solutions
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Ammonia can also react with an Arrhenius acid to form a neutral salt solution! It’s behaving like a base but contains no OH - !
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A more sophisticated definition of acids and bases is needed…
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The Brønsted-Lowry Model
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Brønsted-Lowry Acids Compounds which donate protons (H + ) in aqueous solution Protons cannot exist on their own in aqueous solution. Instead, they ombine with water molecules forming the ydronium n, H + combine with water molecules forming the hydronium ion, H 3 O : HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq)
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Brønsted-Lowry Bases Compounds which accept protons (H + ) in aqueous solution. These protons are typically taken from water molecules forming the ydroxide ion, OH - hydroxide ion, OH : B(aq) + H 2 O(l) BH + (aq) + OH - (aq)
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cid- ase quilibria Acid Base Equilibria When an acid (HA) donates H + to a base (B), the products are A - and BH + : HA(aq) + B(aq) A - (aq) + BH + (aq) Since the products are also an acid and a base, the reverse reaction can occur in which the acid BH + donates H + to the base A - : - q BH + q A q q A (aq) + BH (aq) HA(aq) + B(aq) We therefore have an equilibrium reaction: HA(aq) + B(aq) A - (aq) + BH + (aq)
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Conjugate Acid-Base Pairs Two substances related by the loss or gain of a single proton, H +
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Write the formula and name of the conjugate base for each of the following acids: a. HCN(aq) b. NH 4 + (aq) c. H 2 CO 3 (aq) d. HSO 4 - (aq) ClO q e. HClO 2 (aq) rite the formula and name of the conjugate acid for each of the Write the formula and name of the conjugate acid for each of the following bases: a. CO 3 2- (aq) b. SH - (aq) c. H 2 PO 3 - (aq) d. Br - (aq) e. NO 2 - (aq)
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Acid Dissociation Constant, K a For: A( q + H (l) + q + - q HA(aq) + H 2 O(l) H 3 O (aq) + A (aq) K a = [H 3 O + ][A - ]/[HA] = [H + ][A - ]/[HA] H + is normally used to represent the hydrated proton in acid-base reactions rather than H 3 O + The position of the equilibrium depends on the competition between the two bases H 2 O and A - for the proton is a much stronger base than e equilibrium position will be If H 2 O is a much stronger base than A - the equilibrium position will be far to the right with most of the dissolved acid in ionized form A - a much stronger base than H e equilibrium position will If A is a much stronger base than H 2 O the equilibrium position will be far to the left with most of the dissolved acid in molecular form
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cid Strength Acid Strength A measure of the equilibrium position of its dissociation reaction: HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq)
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Strong Acids he equilibrium position of its dissociation reaction lies far to the The equilibrium position of its dissociation reaction lies far to the right: HCl(g) + H 2 O(l) H 3 O + (aq) + Cl - (aq)
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Strong acids are excellent conductors of electricity since they almost completely dissociate into ions
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This note was uploaded on 04/09/2010 for the course SCIENCE CHEM taught by Professor M during the Spring '09 term at McMaster University.

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14_acids_and_bases - Chapter Chapter 14 Acids and Bases...

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