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13 Dec 2019

Procedures: 1. Obtain a thermometer and place it on the bench at your work area. Be careful it does not roll off the bench. 2. Weigh an empty Erlenmeyer flask with a rubber stopper firmly capping it. Record the mass. 3. Place a small piece of solid CO2 (dry ice) in the flask (use about twice the amount you calculated in pre-lab question c). Place the stopper loosely on top of the flask. Watch the flask while the CO2 sublimes. Firmly stopper the flask immediately after all the solid CO2 disappears. 4. Wait until the flask is equilibrated to room temperature (around 5-10 minutes), and then âburpâ it by lifting one side of the stopper, and then quickly pushing it back in. This is to ensure that the pressure is the same inside and outside the flask. 5. Dry off any accumulated moisture from the outside of the flask, weigh the stoppered flask (on the same scale) and record the mass. 6. To determine the volume of the flask: fill the flask all the way to the brim with water and stopper it while holding it over a sink. If there is any air trapped inside, try again until only water is present inside the stoppered flask. The volume of the water should be the same as the volume of the air in the stoppered flask. Dry off the outside of the flask completely. Measure the volume of water in a graduated cylinder in batches and add up the volumes to get the total volume of all the water in the flask. Record this as the stoppered flask volume. 7. Read the thermometer in your work area and record the temperature. 8. Read the barometer in the lab and record the pressure in mmHg. Ask me if you need help with the barometer. Donât forget to correct the barometer reading for room temperature using the table hanging on the wall. Q: Why do we measure the volume of the flask with water rather than using the volume listed on the side?

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I need help writing a purpose for a chemistry experiment. I feel I was always do a great job, but my professor always disagrees and Iâm out of ideas. The professor wants us to summarize the introduction, and summarize what you will do in each section of the experiment and state how this work will support the goal of this experiment being longer than 1/2 a page. Please, please help me right a better purpose for the experiment below. Thanks.

Experiment 9 Molecular Weight Determination of a Pure Substance Using the Ideal Gas Equation.

Introduction:

The purpose of this experiment is to determine the molecular weight of a volatile, essentially non-polar liquid. An excess amount of pure unknown volatile liquid will be placed into a flask, whose volume will also be determined. The flask will be placed into a hot water bath, whose temperature corresponds to the temperature of the gas in the flask. The liquid will evaporate, driving out the air while the excess liquid evaporates. The pressure of the gas in the flask will correspond to the atmospheric pressure. After the excess unknown liquid has been allowed to evaporate, the flask will be stoppered, cooled, and weighed to determine the grams of the unknown liquid that will be present at the temperature of the water bath as a gas. In this experiment the ideal gas equation will be used PV = nRT = (g/M)RT where R = 0.0821 L*atm/mol*K, T = temperature in K, P = pressure in atm, V = volume in liters, n = moles of gas, g = grams of gas, and M = molecular weight of gas (in units of g/mole). Solving for the molecular weight, M: M = gRT/ PV.

If the molecular weight of a gas is to be determined, the m, T, P, and V must be determined experimentally in the lab. Even though the ideal gas equation is only an approximation of the behavior of gases, molecular weights can still be obtained within 5% of the correct values, as long as volatile non-polar compounds or compounds with only slight amount of polarity are used. For example, C, H, compounds as CH₄ are essentially non-polar, whereas compounds as H₂O are highly polar. Hence, the ideal gas equation would not be a good approximation for describing the behavior of gaseous water.

Procedure:

At the very beginning of the period get a one-liter beaker. Put about 800 mL (your instructor will tell you the exact amount needed) of tap water into the one-liter beaker. Put the one-liter beaker with water onto the hot plate. Set the heat setting of the hot plate to the maximum value. The water in the beaker should be boiling very lightly prior to doing the actual experiment. Therefore, after the water starts boiling in the hot water bath, it may be necessary to cut the heat setting back from highest value. This will take some time. While the water is heating, get the rest of the things needed for this experiment. The setup is shown in figure 1. Record the barometric pressure (in torr to one decimal place). Obtain the rest of the setup consisting of a 250 ml flask, properly prepared rubber stopper with glass tube and aluminum foil, a no-hole rubber stopper, thermometer, and glass stirring rod.

Make sure the 250 mL Florence (or Erlenmeyer) flask is dried (if it is not dry, rinse with 5 mL of acetone, pour off the acetone into the waste bottle in the hood, and then clamp the 250 mL Florence flask onto the ring stand in the inverted position to allow the last traces of acetone to drain out and evaporate. Place the dry no-hole stopper on the flask and weight the flask with the rubber stopper on the balance to 3 decimal places. Record this weight for the weight of the flask plus rubber stopper and moist air. Place 5 mL with a graduated cylinder of unknown liquid into the flask. Place the one-hole rubber stopper, with tube and aluminum foil in the flask. This one-hole stopper, which contains a glass tube that sticks out on the top by 3 mm and is flush with the bottom of the stopper, is covered with aluminum foil with a hole punched into the bottom where the glass tube is. This one-hole rubber stopper is already prepared for you. Push it down firmly into the flask. Remove it. Do this 2-3 times to smooth out the aluminum foil so that the stopper will go down into the flask as much as possible. Then push the stopper down so that it fits snugly but not too tightly to allow it to be removed while the flask is hot. Clamp the flask about the top lip of the Florence flask. That is, the center of the clamp goes about the rim of the flask. Push the flask as far down into the water bath as possible while holding the end of the clamp with your other hand. It is important to be sure that the water in the water bath is always at least 5 mm above there the bottom of the stopper is in the flask. More water may have to be added as some of the water evaporates during the duration of this experiment. (A beaker with hot water (extra) should be present in the hood. One or two of these beakers of hot water should be enough for everyone.) If the water level is not kept to its proper height, the liquid will condense in the upper part of the flask and the excess liquid will never be removed. Be sure that the aluminum foil on top makes a protective wind breaker for the short glass tube sticking out of the rubber stopper so that condensation does not occur there also. As the liquid evaporates from the flask, mix the water in the water bath occasionally and check to see that the temperature remains constant. Record the temperature value of the water bath as the temperature of the gas in the flask for the temperature of the gas would have equilibrated to the temperature of the water bath. After all the liquid has evaporated (takes 2-5 mins for the liquid to evaporate.) from the flask (check carefully that all of the liquid has evaporated-since observing when all the liquid has been evaporated maybe difficult, you should carefully shake slightly the clamp holding the Florence flask to observe the movement of the unknown liquid and when it has disappeared) and none is condensed on the surface walls; (if condensation occurs, be sure all precautions mentioned above are taken) then (these next several steps are to be done quick) remove the rubber stopper with the glass tubing and aluminum foil without excessive shaking. There could be a condensed liquid droplet or two in the glass tube that is not visible. The droplets could drop back into the flask and cause a false high reading for the measured weight of gas in the flask. Immediately replace the rubber stopper (with the glass tube and aluminum foil) with the no-hole stopper, which was used when the flask was originally weighed. This step must be performed quickly to prevent the unknown gas vapors from escaping and being replaced by moist air. Place the no-hole rubber stopper in the Florence flask firmly. Remove the flask from the bath and again check to be sure that the no-hole rubber stopper is firmly in place. Cool the flask by running tap water over the flask for 30-60 seconds. If the stopper is not fitted firmly, air will enter the flask as the liquid inside the flask condenses. As the gas cools and changes to the liquid state, a partial vacuum is created inside the flask. Hence, air will enter the flask if the rubber stopper is not fitted firmly. Completely dry the flask and weigh it on the balance to three decimal places. Record the weight of flask plus stopper and unknown gas.

Repeat this entire procedure a second time and record the date. After, second trial, completely fill the flask with distilled water. Place the no-hole rubber stopper in the flask allowing the excess water to overflow. Wipe the outside completely dry. Then measure the volume of the water in the flask by pouring water into a graduated cylinder. Record this volume.

Experiment 3: Charlesâ Law (Part 2)

Using the air in a flask, measure the change in volume with temperature.

Materials:

2-Hole Rubber stopper
250 mL Erlenmeyer flask
Thermometer
100 mL Graduated cylinder
10 mL Syringe
Syringe dispensing tip

*Microwave or stovetop
*Ice
*Water
*Water bath container

*You must provide

Procedure

Connect the syringe dispensing tip to the end of the syringe.

Set up your experiment by unscrewing the cap off the 250 mL Erlenmeyer flask. Then, press the 2-hole rubber stopper into the 250 mL Erlenmeyer flask. Push the thermometer into one of the holes in the stopper, and the syringe dispensing tip (connected to the syringe) in the remaining hole.

Create an ice water bath by filling an empty container (large enough to fit the 250 mL Erlenmeyer in it) with water and ice. The exact volumes do not matter.

Place the flask in the bath and allow the flask to cool to 0 Â°C (32 Â°F). You may need to pour additional ice around the flask to sufficiently decrease the temperature.

Monitor the temperature until the air reading in the flask is 0 Â°C.

Remove the flask from the ice bath and discard the ice/water from the bath container.

Allow the flask to warm to room temperature. As the flask warms up, record the volume on the syringe and the temperature on the thermometer in Table 4. The volume and temperature at room temperature are the initial (Time = 0) data. Note: The gas in the flask expands as it warms, slowly pushing the piston out of the syringe. The total volume of the gas in the system is equal to the volume of the flask plus the volume of the syringe.

Use the graduated cylinder to measure and add 100 mL of hot (but not boiling) water to the water bath container and place the flask in the warm water.

Continue to record the volume reading on the syringe and the temperature on the thermometer as the gas in the flask heats every five minutes for 30 minutes. Record your results in Table 4.

Table 4: Temperature vs. Volume Data
Syringe Volume (mL) and Temperature (Â°C) at Room Temperature (Step 7)	Time (minutes)	Temperature (Â°C)	Total Volume (mL)
	0
	5
	10
	15
	20
	25

Post-Lab Questions:

Graph your results as temperature vs. total volume. Draw a best-fit straight line through your data pointsand determine the formula for the line in Y = mx +b form. Donât forget to title your graph and label your axes. You may also use a graphing software program for more accurate data plots.

According to your graph, what would the total volume be at a temperature of 70 Â°C? 30 Â°C?

How do your results demonstrate Charlesâ Law? Use mathematical expressions to explain your answer.