When determining the molar mass of a volatile liquid by heating the liquid and then using the condensed, volatile vapor's mass, why do volatile liquids with lower boiling points give better results?
Also, what effect would the formation of dimers have on the experimental molar mass?
Thank you~
When determining the molar mass of a volatile liquid, one common method is to heat the liquid to evaporate it and then measure the mass of the condensed, volatile vapor. The key here is that the liquid should be volatile, which means it can readily evaporate at relatively low temperatures.
Volatile liquids with lower boiling points tend to give better results because they have a higher vapor pressure at lower temperatures. Vapor pressure is the pressure exerted by the vapor of a substance in equilibrium with its liquid or solid phase at a given temperature. The higher the vapor pressure, the easier it is for the liquid to evaporate.
When the boiling point of a volatile liquid is lower, it means that it can evaporate more readily and at lower temperatures. This allows for a more accurate measurement of the mass of the volatile vapor, as it can be collected without significant loss due to condensation or incomplete vaporization.
On the other hand, if the liquid has a higher boiling point, it may not fully evaporate at the experimental temperature, leading to incomplete vaporization. This can result in lower mass measurements and therefore inaccurate determination of the molar mass.
Regarding the effect of the formation of dimers on the experimental molar mass, it depends on the specific circumstances and the nature of the dimer formation. Dimers are formed when two molecules of the same substance join together. In some cases, these dimers can be unstable and easily broken apart, while in other cases, they can be relatively stable.
If the dimer formation is reversible and occurs predominantly in the vapor phase, it can affect the measurement of the molar mass. The presence of dimers can lead to an overestimation of the molar mass because the vapor will contain fewer individual molecules and more of the dimer molecules.
However, if the dimer formation is not reversible or occurs mainly in the liquid phase, it may not significantly affect the measurement of the molar mass. In this case, the dimer would not be present in the vapor phase and therefore would not contribute to the mass of the condensed vapor.
To account for the effect of dimer formation, it is important to consider the specific behavior of the substance being studied. This could involve analyzing the vapor composition and equilibrium constants to determine the extent of dimer formation and its impact on the molar mass determination.