A _____ is used to determine the molecular weight of a substance when its molecular formula is not known.
A)spectrophotometer
B)mass spectrometer
C)systematic balance
D)physical balance
E)mass calorimeter

Question

A _____ is used to determine the molecular weight of a substance when its molecular formula is not known.
A)​spectrophotometer
B)​mass spectrometer
C)​systematic balance
D)​physical balance
E)​mass calorimeter

Quizplus · Accepted Answer

Mass spectrometer is the best choice because it can determine the molecular weight of a substance by analyzing the mass-to-charge ratio of its ions. This method is used when the molecular formula is not known or when the substance is a complex mixture with different molecular sizes. Spectrophotometer, on the other hand, can only measure the absorbance of a substance at a specific wavelength, which is not always correlated with the molecular weight. Systematic balance and physical balance are instruments used to measure the mass of an object, but they cannot determine the molecular weight of a substance. Mass calorimeter measures the heat energy released or absorbed during a chemical reaction or physical change, which is also not directly related to molecular weight.

A _____ Is Used to Determine the Molecular Weight of a Substance