ch302 notes ch7.3 - CH302 Chapter 7 notes part 3 ACIDS and...

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CH302 Chapter 7 notes part 3 ACIDS and BASES Le Chatelier's Principle applied to Dilution of Weak Acids Add enough water so that all concentrations decrease by a factor of 1 0 ystem will move to the RIGHT: Acid will dissociate further! ases! a vs. % Dissociation e if an acid is strong or weak: : .5 ase Definitions oduces OH- ions (very limiting): ON ACCEPTOR the Brønstead-Lowry sense, but eneric Base Dissociation [ ][ ] [] 10 / K 10 HA / 10 / A 10 / O H Q a 3 = = + [ ][ ] HA A O H K 3 a + = S As Q increases back to be equal to K a , the % dissociation incre K Although BOTH indicat K a is CONSTANT for constant T no matter the dilution % dissociation will INCREASE as dilution increases: Fig 7 B Arrhenius: Base pr Brønstead-Lowry definition: A BASE is a PROT We have seen that both water and ammonia can act as acids and bases in that for ammonia AND water together, ammonia acts predominantly as a (weak) base. G eak or Strong Base? eak or strong are WATER SOLUBLE. es: Ca, Ba, Sr hydroxide. have uses as antacids. . less free OH - to hurt your bases that are similar to ammonia, but where one or more H groups are replaced with hydrocarbon groups. W Acids and Bases can be w Base Strength: How much the base breaks apart in solution. Na + (aq) + OH - (aq) strong base ak base eak or Strong? alai metal) hydroxides are STRONG bases. All are STRONG bas nd Al(OH) 3 able 7.3 for values of K b : : Note there are lots of different weak Examples: NaOH (aq) NH 3(aq) + H 2 O (l) NH 4 + aq) + OH - (aq) we ( W ALL Group 1A (alk Only Na and K versions are in common use ($$) Some Group 2A (alkalai earth metals) hydroxides These are NOT very soluble in water. Lower solubility bases like Mg(OH) 2 a insides, but plenty to react with stomach acid! T
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pH of STRONG Base solutions e.g. for NaOH, we will have: NaOH Na + + OH - (aq) (aq) (aq) + and H 2 O (l) H + (aq) + OH - (aq) - - le amount from H O (l) . 0 SSUMPTION BECAUSE K b for a STRONG BASE IS SO LARGE. e have a 0.04M solution of lithium hydroxide, LiOH. H? xample 2: e have a 0.25M solution of barium hydroxide, Ba(OH 2 ). H? The species present are: Na (aq) , OH (aq) , NaOH (aq) , H 2 O (l) , OH (aq) NaOH is a strong base so completely dissociates. Water will only VERY slightly autoionize. We assume ALL the OH - (aq) came from NaOH (aq) , ignoring the miniscu 2 We assume [OH - ] = [NaOH] . 0 - ] = [B] . For STRONG MONOPROTIC BASES [OH THIS IS ONLY A CORRECT A Example 1: W What is the p E W What is the p ple for pH of Weak Monoprotic Base es in 0.15 M aqueous ammonia, Kb = 1.8 x 10 -5 : nother way to see how strong an acid (or base!) is. t dissociation will INCREASE, but K a or K b won't ous example, for ammonia 0.15M: Exam Calculate the concentrations of the various speci Percent Dissociation (see part 2 notes for equation) A A STRONG acid (or base) will be 100% dissociated. Remember: if we DILUTE the acid or base, its percen change. Using the previ
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Example 2: Weak Monoprotic Base e pH of an aqueous ammonia solution is 11.37. Calculate the molarity (original concentration) of the fashion.
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This note was uploaded on 05/01/2009 for the course CH 52410 taught by Professor Sutcliffe during the Spring '09 term at University of Texas at Austin.

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ch302 notes ch7.3 - CH302 Chapter 7 notes part 3 ACIDS and...

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