这是我奋战N个小时完成的化学作业（还有一大堆练习题，但是是手写的，所以不上传了。

Determination of the Molar Mass of Gases and Volatile Liquids Formal Lab Report

Title of lab: Determination of the Molar Mass of Gases and Volatile Liquids.

Purpose of lab: Determine the molar masses of various gases and volatile liquids.

Pre-Lab Questions:

1. Assuming that air is 79%nitrogen, 20% oxygen, and 1% argon, complete the chart.

2. Determine the molar mass of methyl alcohol

Temperature of boiling water bath                        99.5°C

Barometric pressure                                                738 mmHg

Temperature of room temperature water bath 24.0°C

Density of water at room temperature      0.9973g/mL

Mass of condensed methyl alcohol: 1.571-1.557-0.014g

Mass of water in filled pipet: 16.001-1.557=14.444g

Volume of pipet:14.444/0.9973=14.486mL

Molar mass of methyl alcohol (experimental): [0.014g*8.314atm/molK*(273+24)]/[(738mmHg/760mmHg)*(14.486/1000)]=24.3g/mol

Molar mass of methyl alcohol (theoretical): 12.011+15.999+1.008*4=32.042g/mol

Data Tables:

Part 1:  Mass of evacuated syringe:         40.073 g

Part 2:

            Temperature of boiling water bath:                                   98.5 °C

            Barometric Pressure                                                            757.8 mmHg

            Temperature of room temperature water bath     19.1 °C

            Density of water at room temperature                  g/mL

Post-Lab Questions and Calculations:

Part 1:

1. Why can the buoyancy force in this experiment be ignored?

            The syringe is first massed with no air in the same volume, then with a gas in the given volume. Thus, the effect of buoyancy is eliminated.

2. Determine the mass of each gas in the syringe. Enter these values in the Part 1 Data Table.

            Air: Mass of gas: 40.130-40.073=0.057g

            O₂: Mass of gas: 40.142-40.073=0.069g

            CH₄: Mass of gas: 40.117-40.073=0.044g

3. How should the number of molecules trapped in the syringe compare between the various gasses? Explain.

            There should be the same number of molecules trapped in the syringe for each gas, because different gases at the same temperature, pressure, and volume also have the same number of moles.

4. Determine the ratio of the mass of gas/mass of oxygen for each gas. Enter these values in the Part 1 Data Table.

            Air: Mass of gas/Mass of oxygen: 0.057/0.069=0.826

            CH₄: Mass of gas/Mass of oxygen: 0.044/0.069=0.638

5. How should the ratio of the mass of one molecule of gas/mass of one molecule of oxygen compare to the ratio of the mass of gas/mass of oxygen? Explain.

            The first would be comparing the molar mass of the two gases, while the second one would be comparing the mass of the gas in a fixed volume.

6. Use the molar mass of oxygen as a reference to determine the molar mass of each of the other gases tested in Part 1. Enter these values in the Part 1 Data Table.

            Air: Mass of gas/Mass of oxygen: 0.057/0.069=0.826

                        Experimental molar mass: 32.0*0.826=26.432g/mol

            CH₄: Mass of gas/Mass of oxygen: 0.044/0.069=00.638

                        Experimental molar mass: 0.638*32.0=20.416g/mol

7. Determine the accepted molar mass for each gas used.

            Air: Theoretical molar mass: 14.0067*2*0.79+15.999*2*0.2+39.948*0.01=28.930g/mol

            CH₄: Theoretical molar mass: 12.011+1.0079*4=16.043g/mol

8. Determine the percent error in the molar mass values.

            Air: Percent error: (26.432-28.930)/28.930=-8.63%

            CH₄: Percent error: (20.416-16.043)/16.043= 27.3%

9. How do the molar masses compare to the accepted values for each gas tested? Are there any patterns?

            For air, the molar mass was less than expected, while for CH₄ it was more. There is no pattern.

10. Which gases should have the greatest experimental uncertainty? Explain.

            CH₄, because while sucking in the gas, some air might have also gotten into the system.

Part 2:

1. Determine the mass of condensed, volatile vapor for each pipet trial and for each unknown in Part 2. Enter these values in the Part 2 Data Table.

Ethyl Alcohol:

            1: 1.144-1.121=0.023g

            2: 1.140-1.111=0.029g

            3: 1.118-1.098=0.020g

Acetone:

            1: 1.143-1.129=0.014g

            2: 1.104-1.091=0.013g

            3: 1.119-1.107=0.012g

Isopropyl Alcohol:

            1: 1.157-1.127=0.030g

            2: 1.130-1.103=0.027g

            3: 1.125-0.037=0.037g

2. Determine the density of water at the temperature of the room temperature water bath used in this experiment. Enter this density value in the Part 2 Data Table. Use this value and the mass of water

            Pipets used for Ethyl Alcohol:

            1          Mass of water in filled pipet: 5.963-1.121=4.842g

            Volume of pipet: 4.924g/0.998405 g/mL=4.932 mL

            2          Mass of water in filled pipet: 5.978-1.111=4.867g

            Volume of pipet:4.867g/0.998405 g/mL=4.875mL

            3          Mass of water in filled pipet: 5.922-1.098=4.824g

            Volume of pipet:4.824g/0.998405 g/mL=4.832mL

            Pipets used for Acetone:

            1          Mass of water in filled pipet: 6.045-1.129=4.916g

            Volume of pipet:4.916g/0.998405 g/mL=4.924mL

            2          Mass of water in filled pipet: 6.001-1.091=4.910g

            Volume of pipet:4.910/0.998405 g/mL=4.918mL

            3          Mass of water in filled pipet: 6.032-1.107=4.925g

            Volume of pipet:4.925/0.998405 g/mL=4.933mL

            Pipets used for Isopropyl Alcohol:

            1          Mass of water in filled pipet: 5.992-1.127=4.865g

            Volume of pipet:4.865g/0.998405 g/mL=4.893mL

            2          Mass of water in filled pipet: 5.924-1.103=4.821g

            Volume of pipet:4.821/0.998405 g/mL=4.829mL

            3          Mass of water in filled pipet: 5.985-1.088=4.897g

            Volume of pipet:4.897/0.998405 g/mL=4.905mL

3. Determine the mass of the condensed volatile liquids for each run. Enter these values in the part 2 Data Table.

Ethyl Alcohol: 0.023+0.029+0.020=0.072g

Acetone: 0.014+0.013+0.012=0.039g

Isopropyl Alcohol: 0.030+0.027+0.037=0.094g

4. Calculate the molar mass of the liquid used in each run and the average of the three runs for each volatile liquid.

Ethyl Alcohol:

1:[0.023g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.932mL*L/1000mL)]=115g/mol

2: [0.029g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.875mL*L/1000mL)]=146g/mol

3:[0.020g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.832mL*L/1000mL)]=102g/mol

Average: (115+146+102)/3=121g/mol

Acetone:

1:[0.014g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.924mL*L/1000mL)]=70.1g/mol

2:[0.013g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.918mL*L/1000mL)]=65.2g/mol

3:[0.012g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.933mL*L/1000mL)]=60.0g/mol

Average: (70.1+60.2+60.0)/3=63.4g/mol

Isopropyl Alcohol:

1:[0.030g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.893mL*L/1000mL)]=151g/mol

2:[0.027g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.829mL*L/1000mL)]=138g/mol

3:[0.037g*0.08206atm/molK*(292.1)]/[(738mmHg*atm/760mmHg)*(4.829mL*L/1000mL)]=189g/mol

Average: (151+138+189)/=159 g/mol

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

            They reach the gaseous phase faster, thus filling up the space more quickly. Also, the volatile liquids with lower boiling points will also condense quicker.

6. What effect would vapor condensation in the neck of the jumbo pipets have on the reported molar mass? How large an error might this introduce?

            The vapor might not condense, thus having a litter mass. This will introduce a noticeable error, but not by much.

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

            This would increase the experimental molar mass, because if dimers form, there would be less molecules in general, thus decreasing the number of moles and increasing the mass for each mole.

Summary

            The purpose of this entire experiment was to determine the molar masses of various gases and volatile liquids by using a special gas syringe for the gases in Part 1 and evaporating then condensing the liquids in Part 2.

            First, a 60mL gas syringe was found on the lab table, along with a nail and a cap to seal the syringe. The syringe was first evacuated and secured at the 60mL mark, then weighed to nearest 0.001 g. Evacuating and weighing the syringe before filling and weighing the syringe with any other gases was meant to eliminate the effect of buoyancy on the data. The weight of the empty evacuated syringe (40.073g) was obtained and filled into the data table. Then, the syringe was filled with air, and secured at the same mark as with the evacuated syringe. The weight (40.130) was also obtained and filled into the data table. The air was expelled from the syringe, and the syringe was brought to another lab table with two bags of gas, labeled "O₂" and "CH₄" respectively. The syringe was first filled with gas from the bag labeled "O₂", and filled to the 60mL mark. The syringe and gas was then weighed to the nearest 0.001g, and recorded (40.142g). This process was repeated with CH₄, which weighed 40.117g, including the syringe.. This concluded Part 1 of the entire lab.

            Next was Part 2 of the lab. While the original procedure asked for only 3 pipets, it was determined that using 9 pipets would be more efficient. If only 3 pipets were used for the entire part 2, then one must wait for one liquid to finish to continue on to the next one. By having 9 pipets, less time was spent waiting for the previous part to finish.

            The pipets were all stretched so that there was only a small opening at the very tip, thus to make sure that pressure remains the same inside and outside the pipet, while also losing the minimum amount of gas particles when evaporating the liquids. Then, each individual pipet was weighed and recorded. The pipets were labeled as follows: 1_1, 2₁, 3₁, 1₂, 2₂, 3₂, 1₃, 2₃, and 3₃. The large number represented the trial number: Trial 1, Trial 2, Trial 3. The smaller subscript represented the liquid number: ethyl alcohol was ₁, acetone was ₂, and isopropyl alcohol was ₃.  Pipets labeled 1­₁, 2₁, and 3₁ were brought to another lab table and partially filled with ethyl alcohol. Pipets 1₂, 2₂, and 3₂ were partially filled with acetone, and pipets 1₃, 2₃, 3₃ were partially filled with isopropyl alcohol.

            While the pipets and liquids were being prepared, a bunsen burner and stand was set up. A 400mL beaker was used to contain approximately 300mL of water. The bunsen burner was lit, and the water was set on top to boil. A 250mL beaker was filled with water to prepare for the cold water bath. The temperature of this water bath was taken, and was recorded as 19.1 degrees. A LabQuest had been set up in the front of the room, and it showed the pressure to be 738 mmHg.

            When the water began to boil, the temperature was taken and recorded as 98.5^oC. The ethyl alcohol was put in first, and evaporated quickly. The pipets were then placed in the cold water bath, and quickly weighed and recorded. The acetone pipets were placed inside the boiling water immediately after the ethyl alcohol was taken out. While the acetone was evaporating, the ethyl alcohol pipets were flushed and completely filled with water. The mass of the water filled pipets were also recorded. Then, the ethyl alcohol pipets were discarded. The same process happened to both the acetone pipets and the isopropyl pipets (put into cold water bath, weighed, flushed with water, filled with water, weighed again, and then discarded.) After cleaning up the lab area, the lab was completed.

            Post-lab calculations show that there were many errors during the process of the lab. For part 1, the gases sucked into the syringe could have been impure, especially for the oxygen and CH₄, thus leading to large percent errors. For part 2, errors also occurred, as the data from the three trials for each liquid in part two differed greatly. Such an error could have been caused by the overheating of gases, as overheating the gases would have caused most of the liquid to evaporate and escape out of the pipet, or too much air coming inside the pipet. This experiment could've been improved by being careful to put the same amount of liquid into each pipet for each type of liquid. Also, the pipets should have been taken out of the boiling water the moment there was no liquid left in the pipets.

            The experiment was somewhat successful, as it was finished without much obstacles and hardships. However, the data gained differed greatly from what the actual numbers should be(the molar masses were grossly off the mark), making it also somewhat unsuccessful.