Chemical evidence for chain folding in polyethylene crystals is obtained by etching polymer crystals with fuming nitric acid, which cleaves the chain at the fold surface. the resulting chain fragments are separated chromatographically and their molecular weights determined by osmometry. the folded chain is pictured as crossing through the crystal, emerging and folding back, then reentering and recrossing the crystal, and so on. according to this picture, the shortest chain showing up in the chromatograms should equal the crystal thickness in length. the second shortest chain exceeds twice this value by some amount, which measures the length of the loop made by the chain outside the crystal. molecular weights for the two shortest chains observed in an experiment of this sort were 1260 and 2530. since the cleaved chains end in nitro and carboxyl groups, 60 should be subtracted from each of these molecular weights to give polyethylene chain weight. calculate the degree of polymerization of each molecule and the chain length (use the length of the unit cell along the chain axis, 2.53 å, as the distance per repeat unit). compare the latter with the crystal thickness determined by x-ray diffraction, 105 å. what does the ratio of chain lengths for the first and second peaks suggest about the tightness of folding
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Chemistry, 22.06.2019 11:50, hamidaakter936848
Calculate the molarity of each of the following solutions. part a) 0.12 mol of lino3 in 5.5 l of solution part b) 60.7 g c2h6o in 2.48 l of solution part c) 14.2 mg ki in 100 ml of solution
Answers: 2
Chemistry, 23.06.2019 04:31, mdarter
Use the drop-down menus to label each of the following changes p for physical change and c for chemical change. the substance changes to a new substance. the original substance can be recovered. the color changes. gas is produced and given off. the substance changes size, shape, or volume.
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Chemistry, 23.06.2019 05:30, choatefarmsus
Awhite powder is added to a solution. the images show observations made before the powder is added, just after the powder has been added, and a little while later. (the liquid in the small beaker is phenol red solution.) what evidence shows that a chemical change has taken place?
Answers: 1
Chemical evidence for chain folding in polyethylene crystals is obtained by etching polymer crystals...
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