A forensic chemist is given a white solid that is suspected of being pure cocaine (C17H21NO4, molar mass 303.35 g/mol). She dissolves 1.22 ± 0.01 g of the solid in 15.60 ± 0.01 g of benzene. The freezing point is lowered by 1.32 ± 0.04 °C.1 (Kf for benzene is 5.12 °C· kg/mol.) a.What is the molar mass of the substance? Assuming that the percent uncertainty in the calculated molar mass is the same as the percent uncertainty in the temperature change, calculate the uncertainty in the molar mass. b.Could the chemist unequivocally state that the substance is cocaine? For example, is the uncertainty small enough to distinguish cocaine from codeine (C18H21NO3, molar mass 299.36 g/mol)? c.Assuming that the absolute uncertainties in the measurements of temperature and mass remain unchanged, how could the chemist increase the precision of her results?
A
a.What is the molar mass of the substance? Assuming that the percent uncertainty in the calculated molar mass is the same as the percent uncertainty in the temperature change, calculate the uncertainty in the molar mass.
b.Could the chemist unequivocally state that the substance is cocaine? For example, is the uncertainty small enough to distinguish cocaine from codeine (C18H21NO3, molar mass 299.36 g/mol)?
c.Assuming that the absolute uncertainties in the measurements of temperature and mass remain unchanged, how could the chemist increase the precision of her results?
Given that:
Mass of given white solid = 1.22 ± 0.01 g
Mass of solvent(benzene) = 15.60 ± 0.01 g
Freezing point is lowered by 1.32 ± 0.04 °C and Kf for benzene is 5.12 °C· kg/mol.
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