122ch11d - 55 11.79) 56 11.81) 57 11.83) 58 11.85) Ethylene...

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55 11.79)
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56 11.81)
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57 11.83)
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58 11.85) Ethylene Glycol Pentane CH 2 - CH 2 CH 3 CH 2 CH 2 CH 2 CH 3 | | OH OH MW 60 72 b.p. 198°C 36.1°C polar nonpolar LF LF DD H-bonding The two molecules are close in size so have so they have similar LF. Pentane is nonpolar and has only LF. Ethylene glycol, CH 2 (OH)CH 2 (OH), is polar so it also has DD AF. More importantly, ethylene glycol has two OH groups so it can form lots of H-bonds between like molecules. These much stronger AF in ethylene glycol lead to its much higher b.p., viscosity and nonvolatility.
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59 11.90)
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60 11.90) (cont.) b) Octane has a vapor pressure of 13.95 torr at 25°C and a vapor pressure of 144.78 torr at 75°C. Use the CC eqn in part (a) to calculate ) H v .
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61 11.90) (cont.) c) Calculate the normal b.p. of octane (b.p. at 1 atm) d) Calculate the VP at ! 30°C
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62 11.92) a) Both gold, Au, and xenon, Xe, have solid state structures with the fcc u.c. yet Au has a much higher m.p. (1064°C) than Xe (-112°C). Gold is a solid at room temperature (as are all metals, except mercury, Hg) while Xe is a noble gas. Gold is a metallic solid and the atoms are held together by metallic bonding. We can think of metals as having delocalized bonding (orbitals) that cover the whole metal and the valence electrons occupy these delocalized bonds. They essentially consist of an array of positive “ions” (nucleus and inner-core electrons) surrounded by a sea of mobile delocalized valence electrons. The properties depend on the size of the nuclear centers and the number of valence electrons and there is a wide range of hardness and melting point. In any case, this tends to be rather strong AF and the m.p. is above room temp. (solids, except Hg). The m.p. and hardness of metals increases from the outer edges of the metals (group1 and 6) toward the middle of the transition metals, where the metals are very hard with very high m.p. Gold is on the outer edge of the transition metals so you would except a relatively high m.p. Xenon is a molecular solid (even though it consists of only atoms). The atoms are held together by London Forces. These are much weaker than metallic bonding. While Xe is a larger noble gas its LF are much weaker than the metallic bonding found in Au. It will take a lot less energy to break these LF and melt Xe than it takes to break the metallic bonding in Au so the m.p. of Xe is quite low.
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63 11.95) a) Diffraction is the phenomenon in which light waves get scattered as they pass through a narrow slit. When the light passes through many evenly spaced narrow slits (a diffraction grating) the scattered waves interact to form a diffraction pattern (see “A Closer Look - X-Ray Diffraction by Crystals” in section 11.8). The most effective diffraction occurs when the wavelength of the light and the width of the slits are similar in size.
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122ch11d - 55 11.79) 56 11.81) 57 11.83) 58 11.85) Ethylene...

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