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Unformatted text preview: Lab 3: Finding the Partition Constant of an Organic Acid Laboratory Goals In this lab, you will: $ Practice the technique of titration $ Learn to use a separatory funnel $ Demonstrate your proficiency in titration by determining the extent that an acid is partitioned between two immiscible liquids $ Determine the partition constant of salicylic acid between octanol and water Safety Notes 1. Octanol is a volatile, flammable liquid. Do not use any flames during this lab. To reduce fumes (and also the odor), keep a watch glass on top of all beakers containing octanol. If you are in C7, you should use the snorkel hoods to try to minimize the odor. 2. Observe due caution with the sodium hydroxide solution used in this lab. Introduction Intermolecular forces are the basis for some great saying. “Like water off a duck’s back.” or “Oil and water don’t mix.” These sayings indeed have a basis in fact and perhaps you have even seen them in effect with oil and vinegar salad dressing or in the rainbows seen in water puddles with oil in them. We say that such solutions which tend to separate spontaneously are immiscible . This effect has its origins in the interactions between oil molecules (typically long hydrocarbon chains like hexane, CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 ) and the polar water molecules (“polar” refers to the unequal sharing of electrons in the O-H bond–since O is more electronegative the electrons tend to be closer to the oxygen nucleus than to the hydrogen nucleus). As you have learnt in lecture, polar molecules like water have strong intermolecular forces due to its dipole that make favorable, low energy, interactions with each other. Oil and other organic molecules can also do this with each other, although to a greatly reduced extent as they are not polar. Oil and water, and in general nonpolar and polar molecules, are immiscible because mixing would reduce the low energy oil-oil or water-water interactions and increase the higher energy oil-water interactions. Besides being an interesting manifestation of the intermolecular forces between molecules, immiscible solutions play an important role in the environment and in biochemistry. The most important example of an environmentally relevant immiscible solution is an oil spill. A prime example is the MT Tasman Spirit, an oil freighter that had been grounded near Pakistan on August 14 th 2004 containing 67,500 tons of oil. On average, there are over 1000 oil spills into the oceans, sea, lakes, and rivers in the world every year. Although very few are on this scale, each spill can create a huge ecological change for the "infected" area, while also causing minor problems on a much larger scale. An example of the biochemical importance of partitioning of a substance between immiscible solutions occurs in pharmaceutical development. The water/lipid 3-1 partition ratios of drugs are important in understanding their distribution in the body, their mode of action in it, and their excretion from it. of action in it, and their excretion from it....
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This note was uploaded on 04/15/2009 for the course LB 171L taught by Professor All during the Spring '08 term at Michigan State University.
- Spring '08