lab 4 - 1 EXPERIMENT 4 ANALYSIS OF MILK OF MAGNESIA 07F...

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1 EXPERIMENT 4 ANALYSIS OF MILK OF MAGNESIA 07F According to the U. S. Pharmacopoeia, medicinal preparations of milk of magnesia should contain at least 7% magnesium hydroxide by weight. An accurate analysis must measure the total of the suspended and dissolved magnesium hydroxide. To obtain representative samples for analysis, the contents of the bottle must be well shaken first, transferred to a large flask, and stirred while samples are being taken. Because the sample is a white opaque suspension, direct titration poses analytical problems. The suspended magnesium hydroxide particles that adhere to the walls of the flask, out of contact with the titrant, may cause low results and are likely to give a fading end point. A better approach is to use a back titration procedure; that is, add an excess of hydrochloric acid to react with all of the dissolved and suspended magnesium hydroxide to give a clear solution. The excess (unreacted) acid is then (back) titrated with standard sodium hydroxide. The reactions are the following: OH - (aq) + H 3 O + (aq) 2 H 2 O(aq) and/or Mg(OH) 2 (s) + 2 H 3 O + (aq)
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This note was uploaded on 04/13/2008 for the course CHEM 119H taught by Professor Munson during the Fall '07 term at University of Delaware.

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lab 4 - 1 EXPERIMENT 4 ANALYSIS OF MILK OF MAGNESIA 07F...

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