DP Study Guide for Chapter 15

DP Study Guide for Chapter 15 - DP's Study Guide for...

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DP’s Study Guide for Chapter 15 Acids, Bases, and Acid Base Equilibria This is where you need to remember what an acid and a base are and memorize the list of strong acids and bases. Section 15.1 Now that you have a better knowledge of equilibrium the idea of a strong acid or base will make for a more complete description. In the review of CHEM 1, DP made you memorize table 4.1. This is where you use it. We will be using the Bronsted-Lowry theory of acid base reactions. First some notation, hydrogen ion, proton, acidic hydrogen are different names for the same thing. According to these guys and acid is a proton donor and a base is a proton acceptor. There are two main concepts: Capacity and Strength. First Capacity. It may be easier to think of acid/base chemistry as two kids fighting over a small toy, the proton. For example: Ammonia can accept a proton from hydrochloric acid the process shown by: NH 3 + HCl NH 4 + + Cl - One kid is NH 3 the other is Cl - , these two can trade a hydrogen ion between them. To finish this part you have to learn a new word. The word is conjugate. It means similar, yet opposite in function. Girls and boys are something like this, there are some gross similarities, but if you look closer there are differences, and they function differently. NH 3 and NH 4 + look very similar: both having ammonia (one has the proton the other does not). One has the capacity to accept a proton (NH 3 ), so it is the base; after obtaining the proton it is called the conjugate acid (NH 4 + ) because it has the capacity to donate a proton. HCl is the acid and Cl - the conjugate base. Write the reaction backwards: NH 4 + + Cl - NH 3 + HCl Now NH 4 + is the acid and NH 3 is the conjugate base; Cl - is the base, and HCl the conjugate acid. It is common to speak of conjugate acid/base pairs: NH 4 + /NH 3 or HCl/ Cl - Problems: 3, 21, 23 Just as an aside: If you have NOT memorized the polyatomic anions, your ability to ID acids and bases is about zilch. Go find the CHEM 1 Review and do it now. All you have done up to identify who can give or receive protons. Now for the Strength of the conjugate acid/base pairs. Qualitatively review what strength is. A strong acid wants to get rid of its’ proton (just take this proton and shove-it), so its’ conjugate base certainly does not what it back. This gives the strong acid- weak conjugate base rule. A strong base sucks protons like crazy so the resulting conjugate acid holds onto to it, making a weak acid. This gives the strong base-weak acid rule.
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So when to kids fight over a toy, who wins? The meanest kid gets his way. Acetate ion is a weak base, but HCl is a strong acid. HCl wins. Every acetate gets a proton like it or not. The reaction is: CH 3 COO - + HCl CH 3 COOH + Cl Notice the arrow only goes one way. The reaction will continue until either the acetate or HCl is used up. It is not an equilibrium. Amphiprotic: These are molecules which can either act as an acid or a base.
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This test prep was uploaded on 04/16/2008 for the course CHEM 1123 taught by Professor Paul during the Fall '06 term at Arkansas.

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DP Study Guide for Chapter 15 - DP's Study Guide for...

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