Topic: Iodometry
1. The importance of precipitating the Cu2+ ions using NH3 and redissolving it with acetic acid
2. What are other means of detecting endpoint in iodometry aside from adding starch indicator
1. A pH that is too low leads to excessive oxidation of iodide ion to free I2. This reaction is catalyzed by copper(II) ions which makes it worse. Therefore, NH3 is used to form the Cu(NH3)4^+2 which is the intense blue color seen when NH3 is added to the solution. Then acetic acid is added dropwise until the blue color JUST disappears, then a SLIGHT excess of acetic acid is added to make the solution 0.3 M in acid. (Whatever directions you are following means the excess acetic acid in the amount of water called for will be about 0.3 M in acid.)
2. One way, if the solution is colorless, is to let the I2 serve as its own indicator. Also, pentiometric methods may be of some use.
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