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Bond ChangesBefore we go on to the next topic, let's go over the bond changes that took place in exercise 4 and 5. First, in exercise 4 no bond changes occurred, because no mixing took place. Water molecules have hydrogen bonding between the molecules and carbon tetrachloride has van der Waals bonding between the molecules. The bonding between water molecules and carbon tetrachloride molecules would have to be van der Waals because that is all that carbon tetrachloride can do. If any mixing had happened, it would involve breaking van der Waals bonds in the carbon tetrachloride, breaking hydrogen bonds in the water, and forming van der Waals bonds in the mixture. Because that would involve breaking strong bonds to form weak ones, mixing does not happen. When ethanol dissolves in water, things are a little different. In this case both ethanol and water have hydrogen bonding between molecules. Ethanol and water molecules can hydrogen bond to one another. Mixing, in this case, involves breaking hydrogen bonds between water molecules, breaking hydrogen bonds between ethanol molecules, and making hydrogen bonds between water and ethanol molecules. Since the bonds formed are about the same as the bonds broken, mixing does occur. I would like you to go through the rest of those chemicals, those combinations you just worked with, and decide, in each case, what kinds of bonds would be broken and what kinds of bonds would be formed. Once you have done that, check you answers below to make sure that you are properly identifying the bond types that are involved in the mixing or non-mixing as it occurred in each sample. AnswersNote that in the following answers, the answers in quotes are the bonds that would have formed if mixing had occurred. It would also be correct to say that bonds were neither broken nor formed because no mixing occurred. Iodine in water: Break van der Waals and hydrogen, "form van der Waals." Iodine in ethanol: Break van der Waals and hydrogen, "form van der Waals." Iodine in acetone: Break van der Waals and dipole-dipole, "form van der Waals." Iodine in carbon tetrachloride: Break van der Waals, form van der Waals. Sugar in water: Break hydrogen, form hydrogen. Sugar in carbon tetrachloride: Break hydrogen and van der Waals, "form van der Waals." Ethanol in carbon tetrachloride: Break hydrogen and van der Waals, "form van der Waals." Acetone in water: Break dipole-dipole and hydrogen, form dipole-dipole. Acetone in carbon tetrachloride: Break dipole-dipole and van der Waals, form van der Waals.
E-mail instructor: Eden Francis Clackamas Community College |
