4._Chapter_17_acid_base_post

4._Chapter_17_acid_base_post - Acids and Bases(another...

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Ch. 17 Acid-Base 1 Arrhenius Acid: A substance which dissociates to form hydrogen ions (H + ) in solution. HA( aq ) H + ( aq ) + A ( aq ) Arrhenius Base: A substance that dissociates in, or reacts with water to form hydroxide ions (OH ). MOH( aq ) M + ( aq ) + OH ( aq ) Brønsted–Lowry Acid: Substance that can donate H + Brønsted–Lowry Base: Substance that can accept H + Chemical species whose formulas differ only by one proton are said to be conjugate acid–base pairs Acids and Bases (another equilibrium process)
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Ch. 17 Acid-Base 2 Acid–Base Concepts CH 3 COOH + ¯OH CH 3 COO ¯ + H 2 O acid baseconjugate base conjugate acid
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Ch. 17 Acid-Base 3 A Lewis Acid is an electron-pair acceptor. These are generally cations and neutral molecules with vacant valence orbitals, such as Al 3+ , Cu 2+ , H + , BF 3 . A Lewis Base is an electron-pair donor. These are generally anions and neutral molecules with available pairs of electrons, such as H 2 O, NH 3 , O 2– . The bond formed is called a coordinate bond . Acid–Base Concepts FeBr 3 + Br 2 FeBr 4 ¯ + Br + Lewis acid Lewis base Lewis base Lewis acid Arrows makes you think about the electrons and how bonds are formed arrow show bond formation arrow show bond breaking gained two electrons and becomes negatively charged new bond
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Ch. 17 Acid-Base 4 Brønsted–Lowry acids H 2 SO 4 + H 2 O HSO 4 + H 3 O + S O HO O O H O H H H O H H S O HO O O Identify the Lewis acid and Lewis base in each of the following reactions: (a) SnCl 4 ( s ) + 2 Cl ( aq ) SnCl 6 2– ( aq ) (b) Hg 2+ ( aq ) + 4 CN ( aq ) Hg(CN) 4 2– ( aq ) Identify the acids and bases on both sides of the equilibrium
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Ch. 17 Acid-Base 5 Dissociation of Water Water can act as an acid or as a base and amongst themselves, can produce ions (H 3 O + and HOˉ) 2 H 2 O( l ) H 3 O + ( aq ) + OHˉ ( aq ) This is called the autoionization of self-ionization of water. This equilibrium gives us the ion product constant for water and equilibrium constant for this reaction is called K w K w = K c = [H 3 O + ][OHˉ ] = 1.0 x 10 –14 Using arrows show the flow of electrons for this reactions t K w 0ºC 1.14 x 10 -15 10ºC 2.97 x 10 -15 20ºC 6.88 x 10 -15 25ºC 1.01 x 10 -14 30ºC 1.46 x 10 -14 40ºC 2.88 x 10 -14 50ºC 5.31 x 10 -14 100ºC 5.45 x 10 -13 If we know either [H+] or [OHˉ ] then we can determine the other quantity. The equilibrium constant depends on temperature. However, K w is quite small (ranging from 1.14 x 10 -15 for water at its freezing point to 5.45 x 10- 13 at its boiling point Note; Self-ionization of water generates only small amounts of H 3 O + and OHˉ in solution. At 25ºC, about 1 in 555 000 000 collisions leads to ionization
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Ch. 17 Acid-Base 6 What is the [H 3 O + ] and [OHˉ ] in pure water at 0ºC, 25ºC and 100ºC 2 H 2 O( l ) H 3 O + ( aq ) + OHˉ ( aq ) Example pH A Measure of Acidity The pH of a solution is the negative logarithm of the hydrogen ion concentration (in mol/L) . pH = –log [H + ] Acidic solutions: [H + ] > 1.0 x 10 –7 M, pH < 7.00 Basic solutions: [H + ] < 1.0 x 10 –7 M, pH > 7.00 Neutral solutions: [H + ] = 1.0 x 10 –7 M, pH = 7.00
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Ch. 17 Acid-Base 7 pH Scale Chemists usually report the concentration of H 3 O + using the pH scale pH = -log 10 [H 3 O + ]  [H 3 O + ] = 10 -pH In an analogous fashion, we can define pOH as pOH = -log 10 [OHˉ ]  [OHˉ ] = 10 -pOH The relationship between pH and pOH
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Ch. 17 Acid-Base
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