Hi!

there's 3 questions..if you can help on any that'd be great..thanks!

1. Volatile liquids with lower boiling points often give better results than those with higher boiling points. Suggest a reason for this.

2. What effect would vapor condensation in the neck of the 15-mL Beral-type pipets have on the reported molar mass? How large an error might this introduce?

3. Some liquids have enough attractions between molecules to form dimers. (Dimers are molecules formed from the combination of identical molecules, A + A --> A2.) What effect would this have on the experimental molar mass?

You need to give some more details. I have no idea what kind of experiment you are doing. And with regard to question 1, "give better results (for what) than those with higher boiling points.

we are determining the molar masses of various volatile liquids: ethyl alcohol, acetone, and isopropyl alcohol. The liquids are volatized and condensed to a fixed volume. The condensed vapor is massed and the liquid's molar mass is calculated from the experimental data.

sry!..that was me up there!...that's the explanation of the lab.

ffff

Ap Chem lab on Determination of the Molar Mass of volatile liquids.

I am stuck on the same questions.

the answer to number one is along the lines of the results are more accurate with the lower temperatures because the preasure and weight are easier to determine

No problem! I can help you with these questions based on the information provided.

1. Volatile liquids with lower boiling points often give better results than those with higher boiling points. Suggest a reason for this.

To understand why volatile liquids with lower boiling points give better results in this experiment, we need to consider the process of volatizing and condensing the liquids. Volatile liquids evaporate easily and form vapors at a lower temperature, which allows for a faster and more efficient volatization process.

During condensation, the vapors are cooled and converted back into liquid form. Liquids with lower boiling points condense at a lower temperature, meaning they cool down more quickly. This faster condensation reduces the loss of liquid through evaporation during the cooling process, leading to more accurate and reliable measurements.

2. What effect would vapor condensation in the neck of the 15-mL Beral-type pipets have on the reported molar mass? How large an error might this introduce?

If vapor condensation occurs in the neck of the pipets, it can lead to a decrease in the observed mass of the condensed vapor. This is because the condensed vapor in the neck gets mixed with the liquid in the pipet, resulting in an underestimation of the actual mass of the vapor.

The error introduced by vapor condensation in the neck depends on the amount of condensed vapor lost and the accuracy of the measurements taken. The error could range from negligible to significant, depending on the extent of condensation in the neck and the sensitivity of the balance used to measure the mass.

To minimize this error, it is important to ensure proper handling of the pipets, avoiding any excessive cooling or condensation in the neck area. This can be achieved by using a suitable insulating material or gently warming the neck to prevent vapor condensation.

3. Some liquids have enough attractions between molecules to form dimers. What effect would this have on the experimental molar mass?

When some liquids have enough intermolecular attractions to form dimers, the molar mass calculated from the experimental data may be higher than the actual molar mass of the individual molecules. This is because the dimers are counted as one molecule during the calculations, leading to an overestimation of the molar mass.

For example, if the liquid molecules combine to form dimers (A2) during the experimental process, the molar mass calculated would be double the actual molar mass of the individual molecules (2 x molar mass of A). This distortion in the experimental molar mass is due to the presence of the larger dimer molecules.

To mitigate this effect, it is important to account for the presence of dimers when analyzing the experimental data. This can be done by understanding the molecular structure of the liquid and considering the possibility of formation of larger molecular aggregates. By considering the correct stoichiometry and the presence of dimers, a more accurate molar mass can be determined.