AP Chem FRQ: Two liquids with one formula

Short free-response question, 4 pointsAbout 9 minutes · 4 points

1-propanol, CH₃CH₂CH₂OH, and methoxyethane, CH₃OCH₂CH₃, both have the molecular formula C₃H₈O. At 1.00 atm, 1-propanol boils at 97 °C and methoxyethane boils at 7 °C. At 25.0 °C the equilibrium vapor pressure of 1-propanol is 21.0 torr.

(A) Describe a complete Lewis diagram for 1-propanol: the order in which the atoms are bonded, the type of each bond, and the location of every lone pair. 1 point

(B) Explain why 1-propanol has a much higher boiling point than methoxyethane. Your answer should refer to the intermolecular forces in each liquid. 1 point

(C) A sample of liquid 1-propanol is placed in an evacuated, rigid 1.50 L flask at 25.0 °C, and some liquid remains after equilibrium is reached. Calculate the mass, in grams, of 1-propanol in the vapor phase. 1 point

(D) More liquid 1-propanol is injected into the flask in part C, and the temperature is kept at 25.0 °C. Predict whether the pressure of 1-propanol vapor at equilibrium will increase, decrease, or remain the same. Justify your prediction at the particle level. 1 point