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General Chemistry Principles, Patterns, and Applications, 2011

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Would you expect lead glass to be more or less dense than soda-lime glass formed by adding sodium <strong>and</strong><br />

potassium salts as modifiers?<br />

6. Many glasses eventually crystallize, rendering them brittle <strong>and</strong> opaque. Modifying agents such as TiO 2 are<br />

frequently added to molten glass to reduce their tendency to crystallize. Why does the addition of small<br />

amounts of TiO 2 stabilize the amorphous structure of glass?<br />

7. ♦ The carbon–carbon bond distances in polyacetylene (–CH=CH–)n alternate between short <strong>and</strong> long,<br />

resulting in the following b<strong>and</strong> structure:<br />

a. polyacetylene a metal, a semiconductor, or an insulator?<br />

b. Based on its b<strong>and</strong> structure, how would treating polyacetylene with a potent oxidant affect<br />

its electrical conductivity? What would be the effect of treating polyacetylene with small<br />

amounts of a powerful reductant? Explain your answers.<br />

c. Enkephalins are pentapeptides, short biopolymers that are synthesized by humans to control pain. Enkephalins<br />

bind to certain receptors in brain cells, which are also known to bind morphine <strong>and</strong> heroin. One enkephalin has the<br />

structure tyrosine–glycine–glycine–phenylalanine–methionine. Draw its structure.<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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