L07 Chem 111A Quiz: Gen Chem Quiz 1 Notes

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salmonyak403

10 Sep 2015

School

WUSTL

Department

University College - Chemistry

Course

L07 Chem 111A

Professor

Daschbach

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Document Summary

Cathode (attracts cations (+)): negative, anode (attracts anions (-)): positive (electrolytic cell) Flipped cathode ray experiment: positive plate with a negative plate with hole. If in vacuum, no beam will hit the phosphor wall on the other side of negative plate with hole. If with helium gas (actual experiment): beam will hit phosphor due to electrons hitting helium atoms making them he+ causing them to be attracted by negative plate which hit the phosphor wall. When e (total) is positive, the distance between particles is infinite. When e (total) is negative, the distance between particles is finite.

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Please help me finish lab...my lab stopped working and I can'tget the labs to finish. I highlighted and underlined my answers. Ibolded the questions that I could not finish.

1-4: Investigating the Properties of Alpha and BetaParticles

As scientists began investigating the properties of atoms, theirfirst discovery was that they could extract

negatively charged particles. They called these particleselectrons, but they are also known as beta

particles in the context of nuclear decay. Robert Millikan usedbeta particles in his famous Oil Drop

Experiment. Another particle ejected during nuclear decay is thealpha particle. An alpha particle is a

helium nucleus, or a helium atom without its two electrons.Consequently, an alpha particle is positively

charged. Ernest Rutherford used alpha particles in his Gold FoilExperiment.

1. Start Virtual ChemLab and select Alpha and BetaParticles from the list of assignments. The lab will open inthe Quantum laboratory.

2. What source is used in this experiment? Drag yourcursor over the source to identify it.

ElectronGun

What type of charge do electrons have? Negative

What detector is used in this experiment? A phosporScreen

3. Turn on the Phosphor Screen. (Click on the green/redbutton.)

What do you observe? A dot in the center of thescreen

The phosphor screen detects charged particles (such aselectrons) and it glows momentarily at the positions where theparticles impact the screen.

4. Drag the lab window down and left and the phosphor screenwindow up and right in order to

minimize the overlap. Push the Gridbutton on the phosphor screen, and set the Magnetic Fieldto 30

?T. (Click the button above the tens place three times. If youmistakenly click between digits, it will

move the decimal point. Click it to place it where it wasoriginally and then click above the tens

place.)

What happens to the spot from the electron gun on thephosphor screen? the dot moves to theright

5. Click once above the tens place on the ElectricField meter. Observe the spot. Click a second time

above the tens place on the Electric Field.

What happens to the spot from the electron gun on thephosphor screen? The dot moves to theleft

6. Zero out the Magnetic Field and ElectricField meters by clicking on the appropriate digit buttonsuntil the spot on the phosphor screen is centered again.

7. Double-click or click and drag the electron gun to move it tothe Stockroom counter. Enter the Stockroom byclicking inside the Stockroom. Double-click the electrongun to move it back to the shelf. Double-click on the alpha sourceto select it and move it to the Stockroom counter. Clickon the green Return to Lab arrow to return to the lab.Drag the alpha source from the Stockroom counter and placeit on the table where the electron gun was originally placed (themiddle spot light). Click on the front of the alpha source to openthe shutter.

What appears on thephosphor screen?

Atomic Theory

8. Change the unit for the Magnetic Field from ?T to mTby clicking once above the unit. Click above the hundreds placethree times to set the Magnetic Field to 300 mT(millitesla). This magnetic field is one million times strongerthan what we used for the electron gun.

Whichdirection is the spot deflected when the magnetic field isincreased this time?

How doesthis compare with the direction of movement when the magnetic fieldwas turned on for the electrons?

9. Change the unit for the Electric Field from V to kVby clicking once above the unit. Observe the spot as you increasethe Electric Field strength from 0 kV to 5 kV. Themovement is slight so pay careful attention.

Whichdirection is the spot moved when you increase the ElectricField?

How doesthis compare with the direction of movement for the electron beamin the Electric Field?

Why does ittake significantly stronger magnetic and electric field strengthsto move the beam of alpha particles compared with the beam ofelectrons (beta particles)?

10. Return the values on the two meters to zero. Double-click(or click and drag) the alpha source and the phosphor screen toreturn them to the Stockroom counter. Enter theStockroom. Double-click on the alpha source and thephosphor screen to place them on the shelf. Select the laser andthe video camera by double-clicking on them, and then click on thegreen Return to Lab arrow to return to the lab. Place thelaser in the center spotlight on the left and turn the laser on(click on the red/green light). Place the video camera on thecenter spotlight on the right and click the video camera to turn iton. Set the laser intensity to 1 nW and the wavelength to 20 nm.This wavelength is in the x-ray region of the electromagneticspectrum. The purple dot is a representation of the x-rays hittingthe video camera. Change the Electric Field andMagnetic Field to determine the effect on the x-rays.

Did theelectric or magnetic fields affect the x-rays? Why or whynot?

Summarizewhat you have learned about electrons (beta particles), alphaparticles, and x-rays.

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.

(a) A part is made out of two pieces of metal welded together â one iron and one chromium. The part is put into service in a dilute acidic environment with 0.0001 mol/L of HCl acid, 0.004 mol/L of Cr³⁺ cations, hydrogen gas dissolved with an equivalent partial pressure of .01 atm, and no other dissolved constituents, at a temperature of 90^oC. What corrosion reaction(s) will take place? Write both half-cell reactions and the overall reaction. Which material will be the anode and which will be the cathode? The standard emf series is included below. What is the name of the type of corrosion that would occur?

(b) In the situation from part a, what will be the equilibrium potential for the corrosion reaction that takes place? Will the actual corrosion potential be larger or smaller in magnitude than the equilibrium potential, and why?

L07 Chem 111A Quiz: Gen Chem Quiz 1 Notes

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