Gasoline is primarily a mixture of hydrocarbons and is sold with an octane ratin

Question

Gasoline is primarily a mixture of hydrocarbons and is sold with an octane rating that is based on a comparison with the properties of isooctane (C_8 H_18), which has an enthalpy of vaporization of 35.8 kJ/mol and a boiling point of 98.2 degree C where the pressure is 1.00 atm. Determine the vapor pressure of isooctane on a very hot summer day when the temperature is 38 degree C. a. 67.8 torr b. 89.3 torr c. 47.9 torr d. 80.0 torr e. 36.7 torr When sodium chloride dissolves in water, how do the water molecules orient around the ions? a. The oxygen atoms point toward both the sodium and the chloride. b. Around sodium the oxygen atoms point toward the sodium, and around chloride the hydrogen atoms point toward the chloride. c. The hydrogen atoms point toward both the sodium and the chloride. d. Around sodium the hydrogen atoms point toward the sodium, and around chloride the oxygen atoms point toward the chloride. e. Water molecules are randomly oriented around the ions.

Explanation / Answer

Question 6.

Apply Clasius Clapeyron eqution

ln(P2/P1) = dHRxn/R*(1/T1-1/T2)

substitute known data

ln(P2/1) = 35800/8.314*(1/(98.2+273)-1/(38+273))

P2 = exp(-2.24543)

P2 = 0.105882 atm

1 atm = 760 torr

0.105882 atm = 760*0.105882 = 80.47 torr

choose D

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