Exam_U4-KEY - Chemistry 151-KEY Fall 2008 Exam 4 Dr J 1(10...

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Chemistry 151-KEY Fall 2008- Exam 4 Dr. J 1. (10) Hexane (C 6 H 14 ), shown in the figure, is a liquid at room temperature which is insoluble in water (H 2 O). Design a molecular (covalent) compound that might help mix C 6 H 14 and H 2 O into a single liquid phase. Justify your reasoning. A compound that can engage in both H-bonding and dispersion interactions should help mix C 6 H 14 and H 2 O. The compound shown would be a good choice (butanol). H C H H C H H C H H C H H OH The important thinking here is that the compound should share intermolecular force attractions with both. 2. (20) An alcohol is any organic substance that contains at least one hydroxyl functional group (-OH) in its structure. Consider some properties of common alcohols at 20 o C: Substance Boiling Point ( o C) Solubility in water (g/100 mL) CH 3 OH (methanol) 65 Infinite CH 3 CH 2 CH 2 CH 2 OH (butanol) 117 8 CH 3 CH 2 CH 2 CH 2 CH 2 OH (pentanol) 138 2.3 a) How would you justify the observed trends in boiling point and solubility in water? Explain in a sentence. All the alcohols can engage in H-bonding, but a longer chain also allows for additional dispersion interactions. Therefore, pentanol will have the strongest overall intermolecular force attraction and the highest boiling point. On the other hand, methanol is more soluble in water because it can engage in H-bonding and has very little dispersion interactions. So, the H-bonding interaction is strong and the two are soluble.
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