问答题 The sugar fructose contains 40.0/%C，6.7/%H，and 53.3/%O by mass. A solution of 11.7g of fructose in 325g of ethanol has a boiling point of 78.59℃. The boiling point of ethanol is 78.35℃，and K_b for ethanol is 1.20K·kg·mol^-1. What is the molecular formula of fructose? (C₆H₁₂O₆)

【正确答案】Solution： △T_b=T_b-T＇_b=(78.59-78.35)K=0.24K
△T_b=K_b(ethanol)×b(fructose)
=K_b(ethanol)×m(fructose)/M(fructose)·m(ethanol)
M(fructose)=K_b(ethanol)×m(fructose)/△T_b·m(ethanol)
=[1.20×11.7/(0.24×0.325)]g·mol^-1=180g·mol^-1
C:H:O=(180×40.0/%/12.011):(180×6.7/%/1.008):(180×53.3/%/16.00)
=6:12:6
Molecular formula of fructose is C₆H₁₂O₆.

【答案解析】