Lab 10 properties of gases Part B molar mass of a volatile liquid. You can do part B report sheet and post lab questions

PART B: MOLAR MASS OF A VOLATILE LIQUID

MATERIALS: 125-mL Erlenmeyer flask, one-hole rubber stopper with a short piece of glass tubing inserted, 3mL disposable pipette, ImL disposable pipette, two 400-mL beakers, boiling chips, thermometer, utility clamp, hot plate, ring stand, paper towels, unknown liquid, ice, 250-mL graduated cylinder, scissors.

1. Obtain a sample of unknown liquid from your instructor. Record the code number of the unknown liquid on the Report Sheet (1). The unknown liquid will be one of the liquids found in Table 1 (see Report Sheet).
2. Assemble a boiling water bath as in Part A using a hot plate to heat approximately 200 mL of water in a 400 mL beaker (Figure l). Warning: The unknown liquids areflammable — use a hot plate, NOT a Bunsen burner!
3. (Note: This step may be completed beforehand by the lab technician.) Using pliers, gently pull the thin stem of a 3mL disposable pipette until a

very fine (narrow) tip is created.

1. Using scissors, cut and trim the larger end of the 3mL pipette until it fits snugly on the outside of the glass tubing in the stopper assembly, then trim the fine tip to a length of approx. 1 cm (Figure 4). If the tip is frayed or otherwise damaged, obtain a new pipette and repeat Steps 2 and 3.

Figure 4. Stopper assembly with glass tubing and fine-tip pipette attachment.

1. Record the combined mass of a clean, dry 125mL Erlenmeyer flask and stopper assembly on Report Sheet (2).
2. Remove the stopper, and use a ImL disposable pipette to add 0.75 — 1 mL of the unknown liquid to the Erlenmeyer flask – do not exceed I mL of liquid. Replace the stopper assembly firmly in the neck of the flask — the narrow opening of the pipette stem will minimize evaporation of the unknown liquid at room temperature.
3. Attach a utility clamp to the neck of the flask, fasten to the ring stand, and lower the flask into the gently boiling water bath. If necessary, pour additional water into the beaker up to the neck of the flask, leaving a small space at the top so the water will not boil over.
4. The boiling water bath will provide heat to vaporize the contents of the Erlenmeyer flask. Record the temperature of the boiling water (5). This is assumed to be the temperature of the vaporized unknown in the flask (6). Do not let the thermometer touch the sides of the flask or the beaker.
5. While the flask is heating, prepare a cool water bath by adding cool tap water and a few pieces of ice to another 400-mL beaker.
6. Observe the contents of the hot flask: The flask contains more liquid than is required to fill the flask with vapor. As the liquid in the flask begins to vaporize, the liquid level will decrease and excess vapor will escape through the narrow tip of the pipette. At approximately 2-minute intervals, loosen the utility clamp and raise the flask out of the boiling water bath, dry the outside of the flask with a paper towel, observe the amount of liquid present (looking at both the flask walls and the stopper assembly), then lower the flask back in the boiling water bath. When no more liquid is apparent inside the flask or stopper assembly, continue to heatfor an additional 5 minutes. At this point, it is assumed that the Erlenmeyerflask isfilled with only vaporized unknown.
7. Using the utility clamp as a handle, carefully lift the hot flask out of the boiling water bath and place it upright in the cool water bath, until the flask cools to room temperature and droplets of condensed unknown liquid are once again apparent inside the flask (3 – 5 minutes). Record the local barometric pressure while the flask is cooling (7).
8. Remove the flask from the cool water bath, and thoroughly and efficiently dry the outside of the flask and stopper assembly, making sure that no

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water remains or condenses on the outside of the flask.

1. Moving quickly and efficiently, record the mass of the dry flask, stopper assembly, and condensed unknown liquid on the Report Sheet (3). Determine the mass of the condensed unknown liquid (4).
2. Remove the stopper assembly and discard the unknown liquid in the provided ‘Organic Waste’ container. To determine the total volume of the flask, fill the flask to the top with water and reinsert the stopper assembly – some water will spill out. Remove the stopper and pour the wate that filled the flask into a graduated cylinder of appropriate volume. Record the volume of wate in the flask on the Report Sheet (8).
3. Calculate the molar mass of the unknown liquid (9), and use this value to identify your unknown liquid from Table 1 (10).

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Name Dr. S. Partners Bob the Science Dog Date

PART B : Molar Mass of a Volatile Liquid

(1) Unknown liquid code : N/A

(4) Mass of condensed liquid : (3) – (2)

(5) Temperature of boiling water

• 1. Volume of Erlenmeyer flask 155 mL

• 1. Molar mass of the unknown: g/mol

• 1. Identity of unknown liquid from Table I :

Table 1. Volatile Liquid Unknowns

• 1. Calculate % error in Molar Mass:

,RßOPERTIES

REPORT SHEET

Nam e Partners Bob the Science DogDate

PART B : Molar Mass of a Volatile Liquid #2

(1) Unknown liquid code : N/A

1. Identity of unknown liquid from Table 1 :

Table 1. Volatile Liquid Unknowns

1. Calculate % error in Molar Mass:

posr LAB QUESTIONS

Name Partners Date

l. How does temperature affect the kinetic energy of gas molecules?

1. When can a real gas behave as an ideal gas? Are these conditions met in this experiment?
2. What happens to a real gas (e.g., nitrogen gas) as it cools from room temperature to 0 K, absolute zero? Would you expect it to “disappear” when it reached absolute zero? Explain your answer.
3. A sample ⁰ of neon gas occupies 75.0 mL at 25 ⁰C. What is its new volume, in milliliters, if the temperature decreases to -12 C, with P and n constant?
4. A 23.6 g gas sample occupies a 10.0-L flask at 2TC and 780. torr of pressure. Calculate the molar mass of the gas.