A student places a mixture of plastic beads consisting of polypropylene (PP) and
ID: 1039963 • Letter: A
Question
A student places a mixture of plastic beads consisting of polypropylene (PP) and polyvinyl chloride (PVC) in a 1.0 L beaker containing distilled water. After stirring the contents of the beaker vigorously, the student observes that the beads of one type of plastic sink to the bottom of the beaker and the beads of the other type of plastic float on the water. The chemical structures of PP and PVC are represented by the diagrams below, which show segments of each polymer 6. ?? H CH, H CHH CH PVC (a) Given that the spacing between polymer chains in PP and PVC is similar, the beads that sink are made of which polymer? Explain. PP is synthesized from propene, C,Hs, and PVC is synthesized from vinyl chloride, C,H,CI. The structures of the molecules are shown below. CH Cl Propene Vinyl Chloride (chloroethene) (b) The boiling point of liquid propene (226 K) is lower than the boiling point of liquid vinyl chloride (260 K). Account for this difference in terms of the types and strengths of intermolecular forces present in each liquid. In a separate experiment, the student measures the enthalpies of combustion of propene and vinyl chloride. The student determines that the combustion of 2.00 mol of vinyl chloride releases 2300 kJ of energy, according to the equation below. () Using the table of standard enthalpies of formation below, determine whether the combustion of 2.00 mol of propene releases more, less, or the same amount of energy that 2.00 mol of vinyl chloride releases. Justify your answer with a calculation. The balanced equation for the combustion of 2.00 mol of propene is 2 C3H6(g) + 900 ? 6cotg) + 6H2O(g). Substance Standard Enthalpy of Formation (kJ/mol) 37 21 394 24292 0Explanation / Answer
a) Spacing in the polymer chains of PP and PVC are similar but their molecular weights are different. Molecular weight of PVC is more than that of PP. So, PVC is heavier than PP and it sinks into water. PP floats on water.
b) PVC is more polar than PP due to presence of polar C-Cl bonds. So, in this polymer chain dipole - dipole interaction is present. But PP is simple alkane chain which has only weak vandarwaals forces. Dipole - dipole interaction is stronger intermolecular forces than vanderwaals interaction and the stronger intermolecular interactions in PVC increases the boiling point.
c) Energy released from the combustion of 2 moles of propene :
Standard enthalpies of formation of products - Standard enthalpies of formation of reactants
= 4 * (-394) + 2 *(-242) + 2* (-92) - 2*21 - 9*0 kJ = -2286 kJ
So, here the amount of released energy is less than the released energy from the combustion of vinyl chloride.
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