I got think I got the following questions almost figured, but I just want someone to make sure that I am correct.
1) The whole experiment involves using the ideal gas law to predict the molar mass of an unknown liquid. The formula is molar mass of liquid = gR(0.0821)T(temperature in Kelvins) divided by Pressure(atm) multiplied by Volume (liters).
A student did not dry the erlenmeyer flask before weighing it. As a result of this error, would the molar mass be higher or lower than the correct value?
I said that the molar mass would be higher due to there is a greater difference in when one has to subtract the mass of the flask from the mass of the flask with the condensed liquid, there would be a greater difference and the mass of the substance would be calculated to be higher.
2) A student added 0.1mL of unknown liquid rather than 6mL to a 125mL flask. What effect would this action have on the calculated molar mass?
I said that there would be no difference because the volume of the flask is what the volume of the gas will be equal to.
I don't know exactly how the experiment was conducted but I think 1 is right. For 2, however, I think the results must be either too high or too low (but see the note below). If too little liquid is placed in the flask that means that vapor cannot fill the flask so your second weighing weighs all of the vapor produced and some air also. That means the mass of the vapor is too small which will lead to low results. Note: That answer assumes that 0.1 mL doesn't provide enough sample to fill the flask with vapor. If it did the result would not be changed.
1) Your explanation for the first question is partially correct, but let's go over it in a bit more detail to ensure complete clarity. When the erlenmeyer flask is not dried before weighing it, there could be residual water or moisture present on its surface. This will add to the mass of the flask, resulting in an erroneously higher measurement of the total mass of the liquid and flask combined. Consequently, the calculated molar mass of the liquid will also be higher than the actual value.
To get the correct molar mass, it is essential to subtract the mass of the empty, dry flask from the combined mass of the flask and liquid. The presence of additional mass from moisture or water skews this calculation, leading to a higher molar mass result.
2) For the second question, adding only 0.1mL of the unknown liquid instead of 6mL will indeed have a significant effect on the calculated molar mass. As per the ideal gas law, the volume (V) is a crucial variable in the equation. In this case, the volume of the unknown liquid is significantly less than the intended 6mL. This reduction in volume will cause the measured molar mass to be much higher than the actual value.
To obtain accurate results, it is crucial to measure the correct volume of the unknown liquid to ensure the proper application of the ideal gas law. In this scenario, the smaller volume introduced would result in a molar mass calculation that is higher than it should be.
Overall, it's important to pay attention to all the variables involved in the ideal gas law equation, including the cleanliness and dryness of equipment as well as the accurate measurement of volumes.