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CHEM 1320 Study Guide - Torr

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coralsardine455
11 Mar 2014
School
Mizzou
Department
Chemistry
Course
CHEM 1320
Professor
Dr.Tanner

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Document Summary

The purpose of the clausius-clapeyron equation lab was to measure a change in vapor pressure with temperature, and thus measure enthalpy of vaporization. The results from the clausius-clapeyron equation lab clearly indicate that through temperature change you can calculate a change in vapor pressure. 1/t decreased so did ln(pvap), meaning that as temperature increased pvap also increased. Our starting temperature was 278. 15k and initial pvap was 735. 042 torr, as one increased so did that other one, until our final values were 354. 15k and 743. 569 torr. These results show that it is in fact possible to obtain pvap from using temperature change values. Likewise that it is possible to find other unknowns when using the clausius-clapeyron equation. The results did not vary from what was personally expected because as water heats up the pressure is going to increase. Although how this would affect pvap was not known.

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Related Questions

I need help writing a decent conclusion. Every time I submit a lab report the professor slams my conclusion saying it needs work. She wants us to state what the results mean and if they are as expected and explain the possible reasons for variation in your results. The lab is below with data/results. Please, please help.

The Ideal Gas Equation: The Determination of Gas Constant, R

Introduction:

The purpose of this experiment is to determine the gas constant R and the percentage of KClO3 in the KClO3 – KCl – MnO2 mixture using the moles of O2, the original weight of the mixture, and the stoichiometry of the reaction. Consider a plot PV vs. nT for a gas sample where P is the pressure of the gas, V is the volume occupied by the gas, n is the number of moles of gas, and T is the temperature of the gas in Kelvin. If the temperatures and pressures fall in normal ranges, the plot will yield a straight line. Thus, PV = nRT where R is the constant of proportionality between the PV product and the nT product. The object of this experiment is to determine P, V, n, and T for a gas sample and determine the gas constant R, using the equation PV = nRT. The gas sample used will be a sample of oxygen gas generated by the MnO2 catalyzed decomposition of KClO3. Following is the equation of the reaction:

For decomposition of the KClO3 in a KClO3 – KCl – MnO2 mixture, the mass of O2can be determined by taking the difference between the mass of the original mixture and the mass of the residue after the decomposition. This mass is then converted to moles of O2 using the molecular weight of oxygen. The volume of the sample will be determined by water displacement in such a way that the pressure of the sample can be determined from the barometric pressure and the vapor pressure of water. The temperature of the sample will be directly measured.

Procedure:

Assemble the equipment for the apparatus shown in figure 1. With the Florence flask filled to the neck with water, the beaker one-third filled with water, and the pinch clamp open, blow into the tube which connects to the test to create a siphon between the flask and the beaker. Reverse the siphon a few times by raising and lowering the beaker. This will fill the tube connecting the flask and the beaker with water and will also remove air bubbles from the system. Adjust the siphon such that the flask is filled to the neck with water, and close the pinch clamp.

Weigh the eight inch test tube. Add approx. 1.5 grams of the KClO3 – KCl – MnO2mixture to the test tube and weigh the test tube containing the mixture. Record each weight to three decimal places. (Also, be sure and record the sample number for the KClO3 – KCl – MnO2.)

Clamp the test tube to the ring stand, and insert the stopper as shown in figure 1. With the pinch clamp open, raise the level of the beaker such that the water level in the beaker is several inches above the water level in the flask. If a significant amount of water runs into the flask, there is an air leak in the system. If you have an air leak, it must be closed before proceeding. Equalize the pressure in the flask with atmospheric pressure by bringing the water level in the beaker to the same height as the water level in the flask. After closing the pinch clamp, empty and dry the beaker. Open the pinch clamp. A small amount of water will run into the beaker: this will not affect your results since later in this experiment, you will again equalize the pressure in the flask with atmospheric pressure. Ask your instructor to check your apparatus before proceeding.

Heat the mixture with a blue flame until the mixture first begins to melt and then solidifies again; and then heat for an additional 2 mins. (Don’t heat more than 7 mins.) Allow the system to cool for 15 mins. Equalize the pressure with atmospheric pressure, as before; then close the pinch clamp and open the system. Quickly measure the temperature of the gas in the flask; also measure the volume of water in the beaker. Record the barometric pressure reading from professor. Weigh the test tube with the residue and record the mass to three decimal places.

Data/Results:

Trial 1

Weight of test tube

41.912 g

Weight of test tube + mixture

43.343 g

Weight of mixture

1.431 g

Weight of test tube + residue

43.211 g

Weight of oxygen

0.132 g

Moles of oxygen

0.00413 mol

Temperature of water (under oxygen)

21.0 0C

Temperature of oxygen

20.5 0C

Barometric pressure

761.5 torr

Vapor pressure of water

18.7 torr

Pressure of oxygen

742.8 torr

Volume of water displaced

0.101 L

Gas constant, R

61.9

Mass of KClO3 in mixture (use balanced equation)

0.338 g

% of KCLO3 in mixture

23.6 %

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 I’m 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.