I had to do a lab and had to calculate the molar mass for a substance with this equation MM=Mrt/pv but we had to calculate the mass of the substance and its temperature experimently.
My question is why did we have to boil the liquide in a water containing becker.
Why did we have to use the mass of the substance after we evaporate it and cools down why cant we just calculate the mass when it was in liquide form
Boiling the liquid in a water-containing beaker is done as part of the process to determine the molar mass of the substance experimentally. Here's why it is necessary:
1. Boiling the liquid: By boiling the liquid, we ensure that it fully evaporates and is converted into a gas. This is important because the ideal gas law, which is used in the molar mass calculation equation you mentioned (MM = MRT/PV), assumes that the substance behaves as an ideal gas. Boiling the liquid ensures that all the liquid particles are converted into gas particles.
2. Water-containing beaker: The water in the beaker serves as a medium for transferring heat to the liquid. The water absorbs the heat and facilitates the vaporization of the liquid. Heat transfer is essential because it provides the energy required to break the intermolecular forces and transition the liquid to a gas.
Now, regarding the use of the mass of the substance after evaporating and cooling, rather than when it was in the liquid form:
1. Allows for accurate measurement: The mass of a liquid inside a beaker is challenging to measure accurately because there might be residual liquid sticking to the sides or bottom of the container. Additionally, it can be challenging to obtain an accurate measurement due to evaporation occurring during the measurement process. By evaporating the liquid and measuring the mass of the solid residue, we obtain a more accurate measurement of the substance's mass.
2. Eliminates effects of water: If we were to directly measure the mass of the liquid, it would include the mass of any water that may have evaporated along with the substance. By evaporating and cooling down the liquid, we can separate the substance from any water, ensuring that the final mass measurement is only of the substance itself.
In conclusion, boiling the liquid in a water-containing beaker ensures complete vaporization, allowing us to use the ideal gas law for molar mass calculations. Evaporating the liquid and measuring the mass of the solid residue provides a more accurate and precise measurement of the substance's mass, while also eliminating the effects of any water present.