CHM 2045 Lecture Notes - Lecture 8: Ideal Gas, Relative Change And Difference, No. 5 Group Raf

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sapphirecrow670

13 Oct 2015

School

University of Florida

Department

Chemistry

Course

CHM 2045

Professor

Horvath James Charles

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Document Summary

In this experiment, the amount of coating of zinc on nails was measured to determine whether the company that galvanizes nails is charging the right price for its services. Gravimetric analysis and gasometric analysis were used during each trial and compared for effectiveness. Gravimetric analysis was useful for this experiment because it involved measuring the mass lost by nails. Gasometric analysis was useful because it measured a by-product of the reaction to determine the amount of zinc coating. Each nail was weighed before being placed in a flask with hydrochloric acid. The flask had a stopper with rubber tubing that connected to a 100 ml inverted cylinder that was in a 600 ml beaker about halfway full of water. As the hydrochloric acid dissolved the zinc on the nail, hydrogen gas was a by-product and displaced some of the water in the 100 ml cylinder.

Related Questions

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.

1.) average number of moles of NaOH dispensed

2.)average concentration of the acid (mol/L)

3,) Based on your coarse titration volume, do you expect the acetic acid solution to have a higher or lower concentration than the NaOH solution?

higher could you please tell me if number 3 is right

please help with these 2 questions

Part 1: Prepare the NaOH Solution

Lab Results

How many mL of water were used to prepare the NaOH solution?

200mL

Data Analysis

Calculate the molarity of the NaOH solution. The molar mass of NaOH is 39.997 g/mol.

0.1M

Calculate the amount of benzoic acid to be neutralized by 20.00 mL NaOH solution, in both moles and grams. The molar mass of benzoic acid is 122.12 g/mol.

1.207 g

Part 2: Perform a Coarse Titration

Lab Results

Record the following data from your course titration in the table below.

mass of benzoic acid used (g)	0.26614g
pH of benzoic acid solution before titration	2.96
volume of NaOH in the burette before titration (mL)	50.0mL
volume of NaOH in the burette after titration (mL)	28.89mL
volume of NaOH dispensed in the titration (mL)	21.11mL

Data Analysis

How do you expect your coarse titration volume to compare to your fine titration volumes?

I expect the values to be a little off from each other since in the first titration we let out a lot at a time and didnt slowly do the titration. should only be off by a few mL.

Part 3: Perform Fine Titrations

Lab Results

Record the volume of NaOH solution dispensed in the 3 fine titrations.

20 mL dispenced ,20.34mL, 20.30mL

Data Analysis

Calculate the average concentration of the NaOH solution, using the average volume of NaOH solution dispensed in the 3 fine titrations. Report your answer using enough significant figures to distinguish it from the expected concentration of 0.100 M.

V = (V₁ + V₂ + V₃) / 3

V = (20.03 mL + 20.06 mL + 20.02 mL) / 3 = 20.04 mL

M = n / V = 0.00200 moles / 0.02004 L = 0.0998 M

Learning objective: Determine the concentration of a solution.

20.21= ----> 0.0999M

Experiment 2: Use the Standardized NaOH Solution to Determine the Concentration of an Acid

Part 1: Perform a Coarse Titration

Lab Results

What was the pH at the end point of the coarse titration?

3.87ph

Data Analysis

Based on your coarse titration volume, do you expect the acetic acid solution to have a higher or lower concentration than the NaOH solution?

higher

Part 2: Perform Fine Titrations

Lab Results

For the 3 fine titrations of the acid of unknown concentration, fill in the following data.

	Titration #1	Titration #2	Titration #3
volume of acid (mL)	59.11	40.97	40.98
volume of NaOH dispensed (mL)	9.05	9.03	9.02

Data Analysis

Calculate the following quantities and record the data in the table below.

average volume of NaOH solution dispensed (mL)	9.03
average number of moles of NaOH dispensed
average concentration of the acid (mol/L)

Conclusions

Phenolphthalein is pink over the range of pH 8 â 12. Why was it a useful indicator of when the equivalence point was reached?

This was helpful because once I got to the ph of 7 I knew that I would be getting closer to the end point which would change the color to pink.

Suppose a student titrated a sample of monoprotic acid of unknown concentration using a previously standardized solution of NaOH.

volume of 0.125 M NaOH dispensed	24.68 mL
volume of acid solution	50.00 mL

Given the data in the figure above, what is the concentration of the unknown acid?

0.0617M

Lab NOTES:

ex1

Take sodium hydroxide from the Materials shelf and add 0.800 g to the beaker.

Take water from the Materials shelf and add 200 mL to the beaker.

Ph 2.96

inital volume in burett

inital volume 50ml

1.) volume43.78mL

volumes dispenced =6.22ml

2. volume =38.05

volume dispenced =11.95ml

3.)volume = 32.06

volume dispenced=17.94

4.28.89ml

volume dispenced=21.11ml

ph=10.95

--------------------------------------

Ex 2

inital ph= 2.96

volume30.33

dispence 20.05

1. volume 39.92ml

volume dispenced=10.08

2.volume 29.66

voiume dispence 20.34

final ph10.43

initial valume in burett 50ml

--------------------

ex3

final ph9.43

volume 30.28

volume dipenced=20.00

----------------------------------------------------------------------

2nd Ex

initial ph 3.11

volume 50

1. volume 48.95mL

dispenced 1.05mL

ph 3.87

2. volume 45.88

dispenced 4.12

ph 4.67

3 volume 42.99

dispenced 7.01

ph 5.29

4 volume 39.93

dispence 10.07

ph 11.45

--------------------

final ph 9.99

volume 59.11

dispenced 9.05

ph 9.59

volume 40.97

dispenced 9.03

ph 9.50

volume 40.98

9.02

I need help writing a purpose for a chemistry experiment. I feel I was always do a great job, but my professor always gives me 3 out of 6. Iâm out of ideas. She 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. She also said not to go into depth on calculations just summarize each section in procedure. Please, please help me right a better purpose for the experiment below. Thanks.

Experiment 5 Analysis of Copper in a Brass Sample

Introduction

A.General

The purpose of this experiment is to determine the percentage of copper present in an unknown brass sample spectrophotometrically using a Spectronic 20. Brass is an alloy consisting of tin, lead, copper, and zinc. The brass sample has already been ground to a fine powder.

A standard curve (graph) will be made for Cu⁺² in which a plot of absorbance (instrument reading from the Spectronic 20) versus molarity of Cu⁺² for various solutions will be made. These standard Cu⁺² will be made by dissolving the appropriate amount of CuSO₄ * 5H₂O is distilled water. The brass samples will be made by dissolving the brass in concentrated HNO₃ to produce Pb⁺², Cu⁺², Zn⁺² is solution along with the finely divided white hydrated tin (IV) oxide solid. After the properly prepared solutions have been filtered to remove the tin (IV) oxide, the absorbance of these solutions will be measured using the Spectronic 20. The molarity of Cu⁺² in these solutions will be obtained from the standard curve. Then the percent copper in the brass sample will be calculated.

B.Method of Analysis

In each of the 5 solutions (3 for determining the standard curve and 2 for the determination of copper in brass) the molarity of Cu⁺² present will be determined spectrophotometrically using the Bausch & Lomb Spectronic 20. The only species in the solution that absorbs at 620 mÂµ (this wavelength corresponds to the visible portion of the electromagnetic waves) in Cu⁺². In this aqueous solution Cu⁺² is really present as the aquo complex [Cu(H₂O)₆]⁺². The other species Pb⁺², Zn⁺², H⁺, NO₃^-, SO₄^-2, and H₂O do not absorb at the 620 mÂµ wavelength of light (and tin is precipitated as hydrated tin (IV) oxide).

In the Spectronic 20, light of wavelength of 620 mÂµ and certain initial intensity, I₀ is allowed to pass through the sample. The wider the sample tube (width = b) and the greater the molarity of Cu⁺², the more absorption will occur causing the intensity of the 620 mÂµ wavelength (I) to be less as it leaves the solution. The following equation describes the process quantitatively: A = log I₀ / I = abM, where A = absorbance (quantity actually measured by the Spectronic 20), M = molarity of the absorbance species (Cu⁺² in this experiment), b = tube diameter, and a = constant which is characteristic of each absorbing species. Since the same tube (a special tube called a cuvette is used for spectrophotometry) is used throughout the experiment, b remains constant. Hence, we can define a new constant, K = ab. Therefore, the above equation becomes: A = KM = K [Cu⁺²]. A plot of A (the absorbance value measured by the use of the Spectronic 20) versus the molarity of Cu⁺² should be a straight line going through the origin (A = 0.000 and M = 0.000).

Three standard Cu⁺² solutions will be made by dissolving a known amount of CuSO₄ * 5H₂O in distilled water. Hence, the molarity of these solutions will be known. Then the absorbance value for each of these three solutions will be measured using the Spectronic 20. A plot of the three absorbance values versus the corresponding Cu⁺² molarities will be done. The best straight line is drawn through these three points and the origin.

With the standard curve, the molarity of Cu⁺² in any Cu⁺² solution can be determined by measuring the absorbance value of the solution (always using the same cuvette and Spectronic 20) and referring to the standard curve to find the molarity of Cu⁺² that corresponds to that absorbance value. Thus, the molarity of Cu⁺² in the brass sample solutions can be obtained from the standard curve after their absorbance values have been measured on the Spectronic 20.

Procedure

Preparation of Brass Sample Solutions

Weigh two brass samples between 0.6 to 0.8 g (to three d.p.). This is done by putting a small clean, dry beaker (100 or 150 mL) on the pan of the balance. Zero the balance. Carefully add the unknown to the beaker until you get a weight somewhere between 0.6 to 0.8 g (Record to 3 d.p.). To each beaker (under the hood) add 12 mL of 8 M nitric acid very slowly. The reaction of 8 M acid with the finely divided brass sample occurs vigorously. The 8 M must be added slowly to prevent splattering of the brass sample out of the container. The reaction is performed in the hood to prevent toxic brown NO₂ gas from entering the lab. After the initial reaction, leave the beaker in the hood but mix occasionally over 30 mins (during this 30 mins the known CuSO₄ * 5H₂O solutions (Part B) can be measured on the Spectronic 20.)

After the brass has reacted with the 8 M nitric acid, wash down the sides of the beaker with some distilled water from a squeeze bottle. Quantitatively, with no spillage transfer the mixture to a clean 50 mL volumetric flask. After solution is poured into the volumetric flask, add more distilled water to the beaker, washing the sides of the walls. Pour this quantitatively into the volumetric flask as mentioned above. Repeat this two more times. Then add enough distilled water until the 50.00 mL mark is reached by the bottom of the meniscus of the solution. Stopper and mix very well by continually shaking the flask in the upright and inverted positions.

The blue solutions must be filtered to remove the tin (IV) oxide or an incorrect high reading will be obtained for the absorbance reading due to the scatter of the light waves. Filter each of the solutions through dry Whatman No. 1 filter paper. (Use 2 pieces to avoid another filtration. Place one piece on the other. Fold in half and then fold in half again. Open it up into a cone and place it into a filter funnel.) Collect the filtrate in clean, dry beakers. If the filtrate is not a clear pale(blue) color, then another filter again with new Whatman filter paper and with clean, dry beakers. One to three filtrations maybe needed, depending on how much tin was present in the brass sample. Now measure the absorbance of these two solutions as described in the section âUse of the Spectronic 20.â Be sure you do these absorbance measurements and the three from part B on the same Spectronic 20.

Preparation of known CuSO₄ * 5H₂O solutions

The three known (standard solutions have already been prepared for you. They are ready for use in their cuvettes by the side of the Spectronic 20 instrument. These three solutions were prepared for you by the stockroom personnel as described in the procedure in the next paragraph. All you need to do is to measure the absorbance of these three prepared standard solutions.

Weigh three 50 mL volumetric flasks (to 3 d.p.). To each of these volumetric flasks add about 1.000, 2.000, and 3.000 grams of CuSO₄ * 5H₂O. Again weigh the volumetric with the CuSO4 * 5H2O (to 3 d.p.). Add 6.0 mL of concentrated nitric acid (measured with a graduated cylinder) and approx. 25 mL of distilled water to each flask. Mix until CuSO₄ * 5H₂O dissolves. Then add distilled water until the bottom of the meniscus of the solution hits the 50.00ML mark. Stop and mix well (as previous section for making the brass solutions). Measure the absorbance of each solution as described in the section âUse of the Spectronic 20.â Be sure you do these absorbance measurements and the three from part A on the same Spectronic 20.

Use of Spectronic 20

How to use the Spectronic 20 and measure the absorbance of each solution is described on another document I will give. Remember wavelength should be set at 620 mÂµ.

CHM 2045 Lecture Notes - Lecture 8: Ideal Gas, Relative Change And Difference, No. 5 Group Raf

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