BubblesNRBaking soda BubblesNRMagnesium *Yellow*BlueBromothymol *Cloudy/ white *PinkPhenolphthalein RedBlueLitmus (blue or red) pH (# from the key) Not slipperySlippery Feel (choose slippery or not slippery) SourBitterTaste AcidBase Acid and Base Properties *Usually, but not always

pH There are many ways to consider acids and bases. One of these is pH. [H + ] is critical in many chemical reactions. A quick method of denoting [H + ] is via pH. By definition pH = – log [H + ], [H + ] = 10 -pH The pH scale, similar to the Richter scale, describes a wide range of values An earthquake of “6” is 10  as violent as a “5” Thus, the pH scale condenses possible values of [H + ] to a 14 point scale Also, it is easier to say pH = 7 vs. [H + ] = 1 x 10 –7

Calculations with pH Ans: x 10 –8 M Q: What is the pH if [H + ]= 6.3 x 10 –5 ? pH = – log [H + ] (‘6.3’, ‘exp’ or ‘EE’, ‘5’, ‘+/-’, ‘log’, ‘+/-’) (‘-’, ‘log’, ‘6.3’, ‘exp’ or ‘EE’, ‘-’, ‘5’) Q: What is the [H + ] if pH = 7.4? [H + ] = 10 –pH mol/L (’10’, ‘x y ’, ‘7.4’, ‘+/-’, ‘=‘) (’10’, ‘^’, ‘-’, ‘7.4’, ‘=‘)

2 a)pH = – log [H + ] = – log [1x10 –8 ] = 8.0 b)pH = – log [H + ] = – log [1x10 –7 ] = 7.0 c)pH = – log [H + ] = – log [2.5x10 –6 ] = 5.60 d)pH = – log [H + ] = – log [1.3x10 –4 ] = a)[H + ] = 10 –pH = 10 –5.4 = 4 x 10 –6 mol/L b)[H + ] = 10 –pH = 10 –5.72 = 1.9 x 10 –6 mol/L

Historical views on acids Arrhenius acids and bases Arrhenius acid forms H 3 0+ (hydronium ion) Arrhenius base forms OH- (hydroxide ion) Ionization + ClH H H O + H H HO + O (e.g. H 2 SO 4 ) was originally thought to cause acidic properties. Later, H was implicated, but it was still not clear why CH 4 was neutral. Arrhenius made the revolutionary suggestion that some solutions contain ions & that acids produce H 3 O + ions in solution.

Lewis Acid In 1923, G. N. Lewis (yes, the Lewis structure guy) suggested a way of describing a number of reactions that did not fit the Bronsted definition of acid-base reactions, yet seemed to have some unifying structural features. He suggested: A Lewis acid is an electron pair acceptor. Lewis base is an electron pair donor. The simplest reaction is for a Lewis acid to interact with a Lewis base to give a Lewis acid/base complex: A + B  A-B

Lewis acid/base Example Note several things about this reaction: They are charge balanced - that is the total charge of all species is the same on both sides of the equations The product is sometimes described as a Lewis "complex"

The Bronsted-Lowry concept In this idea, the ionization of an acid by water is just one example of an acid-base reaction. Acids and bases are identified based on whether they donate or accept H +. “Conjugate” acids and bases are found on the products side of the equation. A conjugate base is the same as the starting acid minus H +. + ClH H H O + H H HO + acidbase conjugate acidconjugate base conjugate acid-base pairs

Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: acidbase conjugate acidconjugate base HC 2 H 3 O 2 (aq) + H 2 O (l)  C 2 H 3 O 2 – (aq) + H 3 O + (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base OH – (aq) + HCO 3 – (aq)  CO 3 2– (aq) + H 2 O (l) conjugate acid-base pairs

acidbase conjugate acidconjugate base HF (aq) + SO 3 2– (aq)  F – (aq) + HSO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base CO 3 2– (aq) + HC 2 H 3 O 2 (aq)  C 2 H 3 O 2 – (aq) + HCO 3 – (aq) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 PO 4 (aq) + OCl – (aq)  H 2 PO 4 – (aq) + HOCl (aq) conjugate acid-base pairs Answers: question 18 (a) (b) (c)

acidbase conjugate baseconjugate acid HCO 3 – (aq) + S 2– (aq)  HS – (aq) + CO 3 2– (aq) conjugate acid-base pairs baseacid conjugate acidconjugate base H 2 CO 3 (aq) + OH – (aq)  HCO 3 – (aq) + H 2 O (l) conjugate acid-base pairs acidbase conjugate acidconjugate base H 3 O + (aq) + HSO 3 – (aq)  H 2 O (l) + H 2 SO 3 (aq) conjugate acid-base pairs 8a) 8b) 11a) baseacid conjugate baseconjugate acid OH – (aq) + HSO 3 – (aq)  H 2 O (l) + SO 3 2– (aq) conjugate acid-base pairs 11b) For more lessons, visit