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Department
Biochemistry
Course
BIOCH499A
Professor
Gail Amort- Larson
Semester
Winter

Description
1 2 Chapter 18 – Acids & Bases Speed Bump by Dave Coverly  Arrhenius definition  Brønsted-Lowry definition  Acid strength and water ionization constant  pH and pOH  Strong acids and strong bases  Weak acids  Weak bases  Polyprotic acids  Acid-base properties of salt solutions  Lewis definition 3 4 Overview of acid-base chemistry Arrehnius definition (~1900) + Acids and bases appear in many aspects of our lives. Acids produce H in solutions. – Some (among many) examples: Bases produce OH . Acids H 2O 4 One of the most produced chemicals in the  + – HA (aq)  H + A world. Important application in car batteries. BOH  B+ + OH – Food Citric acid – juice (aq) Examples Ascorbicditamin)  + – Pharmaceutical drugs acetylsalicylic acid (aspirin) HCN (aq) H + CN DNA Amino acids Mg(OH)  Mg +2 + 2 OH – 2 (aq) Bases Limitations Detergents Ammonia, cleaners – only aqueous solutions Food BakingdNaaHCO – only base is the OHon 3 DNA (adenine, guanine, cytosine and thymine) 5 6 Brønsted-Lowry definition (1923) – Acids are proton donors See figure 18.8 – Bases are proton acceptors In acid-base rxn, a proton is transferred from the acid to the base. + – HA + B  BH + A acid base conjugate acid conjugate base Examples Note that water can be either an acid or a base in a  + – Bronsted–Lowry acid–base reaction. CH 2O  H 3 + CN H O + is called the hydronium ion 3 + + H 3 is equivalent to H 7 8 Acid strength Water ionization constant Strong acids complete dissociation Water can be an acid or a base +  Weak acids partial dissociation H 2 + H 2  H 3 (aq) OH (aq) See Silberberg Fig. 18.9 for acid vs. conjugate base Or simplified H 2O (l)  H +(aq) OH  (aq) strength. +  Equil. constant K w = [H ][OH ] At 25C, K = 1.0 x 10 w +  Pureater[H ] = [OH ] K = [H[]or +] = 1.0 x 10 M = [OH ] w +  In most solutions [H ]  [OH ] In tap water, say [H] = 3
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