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3.091 Introduction to Solid-State Chemistry - Fall 2013

Problem Set 13

Evaluation to be held on the final

1. There are two stereo isomers of butene, cis 2-butene and trans-2-butene. Whichmolecule has a larger dipole moment? Which has higher boiling point?

2. Two specimens of polyethylene, one composed of linear chains and the othercomposed of branched chains, are solidified by identical cooling from the melt.

The degree of polymerization is the same for both specimens. What is more

likely to be suitable for use as a plastic food wrap?

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3. Draw a trimer of isotactic polypropylene

4. Acrylonitrile, H2C=CH-CN, can be reacted by addition polymerization to formpolyacrylonitrile (PAN). Draw a segment of syndiotactic PAN showing four

repeat units.

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5. 1-chlorobutene, ClHC=CH-CH2-CH3, can be reacted to form isotacticpolychlorobutene (PCB)

a. Does the reaction occur by addition or condensation?b. Draw a trimer of isotactic PCBc. What is the value of the degree of polymerization, n, of isotactic PCB with

a molecular weight of 3 x 105 g/mole?

d. Is isotactic PCB a thermoset or a thermoplastic? Explaine. Draw a schematic representation of the temperature dependence of the

volume of linear isotactic PCB and branched PCB assuming both to be of

comparable molecular weight. Label the Tg of both substances.

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6. Calculate the root mean squared length of a polypropylene molecule withmolecular weight of 100,000 gm/mole.

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7. A particularly strong rigid polyester used for electronic parts is marketed underthe trade name Glyptal. It is a polymer of terephthalic acid and glycerol. Draw a

segment of the polymer and explain why it is so strong.

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8. Explain why a much stiffer foam is obtained if small amount of glycerol is addedto the reaction mixture of toluene-2-6-diisocyanate and ethylene glycol during

synthesis of a polyurethane foam.

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9. Estimate the surface energy of the (100) face of Rh crystals given just theinformation in the periodic table.

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10.Estimate the surface energy of the (110) face of K crystals given just theinformation in the periodic table.

11.How much larger will the surface energy be for a (100) face of Pt crystal if it ismiss cut by 5 degrees?

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12.What facets do you expect to appear on single crystals of Pt? What will be theequilibrium shape for these platinum crystals?

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13.Two crystals of Pd are sitting next to one another. One has overall dimension ofone micron the other has overall dimension of five microns. Which crystal has

the larger energy per unit volume? How could the total energy be decreased?

14.The surface tension of an aqueous solution of a molecule is measured as afunction of concentration. The data is shown below. Explain what is happening

and why. How will the appearance of the solution differ at 0.001 wt% versus 1

wt.%?

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15.Sketch how you expect the conductivity of an aqueous solution of SDS(CH3(CH2)11OSO3Na) to vary with concentration. Label all the relevant features

of your sketch.

16.Sketch how you expect the surfactant surface concentration at the air waterinterface to change with aqueous solution concentration of the surfactant.

Explain all relevant features of the sketch.

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17.A surfactant known as Brij 30 has the structure C12H25(OCH2CH2)4OH. Sodiumdodecyl sulfate (SDS) has the structure CH3(CH2)11OSO3Na. Which of these two

surfactants has the lower CMC? Briefly explain your reasoning.

18.Why might SDS (CH3(CH2)11OSO3Na) form spherical micelles andphosphatidylcholine (shown below) form bilayer aggregates?