10. Challenge. Naphthalene is a hydrocarbon with 93.71% carbon by mass. A 0.256-

Question

10. Challenge. Naphthalene is a hydrocarbon with 93.71% carbon by mass. A 0.256-mol sample has a mass of 32.8 g. Naphthalene works as a pesticide in mothballs by sublimation of the solid so that it fumigates enclosed spaces with its vapors according to the equation: naphthalene(s)naphthalene(g) Kc = 4.29 × 10-6 1 at 298 K. If 3.00 g of solid naphthalene is placed into an enclosed space with a volume of 5.00 L at 25°C, what percentage of the naphthalene will have sublimed once equilibrium has been established?

Explanation / Answer

molarity = grams solute/molar mass solute x L of solution

molar concentration of naphthalene in solution = 3 g/128.17 g/mol x 5 L

                                                                           = 0.0047 M

at equilibrium

ICE chart

                naphthalene(s) <===> naphthalene(g)

I                     0.0047                                -   

C                       -x                                  +x

E                  0.0047-x                              x

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Kc = [naphthalene(g)]/[naphthalene(s)] = 4.29 x 10^-6

4.29 x 10^-6 = x/(0.0047-x)

2.0163 x 10^-8 - 4.29 x 10^-6x = x

x = 2.0163 x 10^-8/1.00 = 2.1063 x 10^-8 M

Percentage of naphthalene sublimed = (2.0163 x 10^-8 M/0.0047 M) x 100 = 0.00043%

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