CHEM-115 Midterm: CHEM 115 Georgetown Exam1(2002)

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turquoisegnu128

15 Feb 2019

School

Georgetown University

Department

Chemistry

Course

CHEM-115

Professor

All

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Please read each question carefully before you begin. Your exam should have a total of 6 pages. You will have two hours in which to complete this exam; be sure to save time to check your answers after you"re finished. The backs of the pages may be used for rough work, but your answers should be written clearly on the front of the page in the spaces provided. Show your work clearly, and you may receive partial credit for partially correct answers. Energy costs for interactions in alkane conformers (e in kcal/mol) Energy difference between the axial and equatorial conformations of substituted. Ch3 (b) (c: (5 pts each, 15 total) draw a structure for each compound (low energy conformation please). (a) (ch3)3cch2ch(c(ch3)3)ch2ch3. Page 3 of 6 (b) spiro[5. 2]octane (c) cis-decalin. 1 bonus point for the iupac name of molecule (c) ___________________________________: (10 pts) briefly explain the difference in meaning of the double arrows in the following two expressions.

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PROCEDURES :

Rinse and flush a burette with the solution of NaOH provided and set it up. Fill the burette with the solution of NaOH solution.

Using a 15-mL volumetric pipette, collect an accurate volume of the 0.1 M HC1 solution and add it to a 250-mL beaker that contains about 50-mL of deionized water and a magnetic stir bar. Place the beaker on a stir plate and begin stirring.

Turn on the Vernier LabQuest by pressing the silver power button in the upper left corner. Connect a pH probe into the slot marked CH 1, this slot is located on the top edge of the LabQuest. The LabQuest will automatically recognize the type of probe and begin to display the pH data.

Using the stylus provided tap the tabs displayed at the top of the screen to toggle between the Meter screen, Graph screen and Data Table screen.

Conduct the titration by adding the basic solution from the burette to the acid solution. You should take the pH reading after every addition of I.00 mL of the base solution. Continue the titration process until you have added 30.00 mL of the base solution.

Rinse the probe several times with tap water followed with deionized water.

Insert the clean probe you just rinsed in the acid solution labelled X and determine its pH.

Insert the clean probe you just rinsed in the base solution labelled Y and determine its pH.

Dispose the waste according in the labeled waste disposal container.

graph of pH vs. volume of NaOH solution added that will be graded according to the graph guidelines provided below;

GRAPH GUIDELINES

Submit a FULL PAGE OF titration curve by stapling it to this report sheet. Your graph will be graded based on the âChemistry Graph Checklistâ posted on Blackboard, which includes overall appearance. You may seek out help from peers while learning to use Excel, but your graph must be your own.

1. Appropriate tittle (5 points)

2. Correct labelling of both axes (10 points)

3. Correct units on both axes (10 points)

4. Graph occupying at least Â¾ of the page used (5 points)

5. Correct scales for both axes (10 points)

6. General shape of the graph (10 points)

Please someone helps me I did it but i dont know what im missing

can someone complate what I miss

How is the binding of F- to cations minimized in your experiment.

CHEM 319, QUANTITATIVE ANALYSIS LA8ORATORY EXERCISE à¸®6 QUANTIFYING FLUORIDE USING AN ION SELECTIME ELECTRODE PRE-LAD READING Read Harris pages 303-306 311-317 (on-selective electrodes) Lean how to prepare samples for analysis from dmicut to wark with starting materials Learn how to prepare calibration curves from ISE data EXPERIMENT OVERVIEW For this lab, you will determine the fuoride content in commercial mouthwashes using an ion selective electrode. This lab uses the direct potentiometry method, which assumes that matrix interferences are not a problem for determining the concentration of fuoride in toothpaste. To combat possible matrx problems, the total ionic strength adjustment buler (TISAB) solution used in the experiment contains 12 gand ensures that cations of meta's such as iron and copper in the sample will not complex the fuoride on. The TISAB will also adjust and stablize the lonic strength of the measured solutions lonic strengt can be a large factor affecting accuracy in ion selective electrode (ISE) measurements MATERIALS Total ionic strengh adjustment bulffer (TISAB) Fluoride stock solution (500 ppm wv) Two commercial mouthwashes (one control and one unknown) Fluoride lon selective electrode 10 mL volumetric fasks Sar bars 20-mL vials 1. Prepare five 10 mL standard solutions (2 ppm. 5 ppm, 20 ppm. 50 ppm, and 100 ppm)each containing 50%w/v ofthe TISAB andthe residual volumne comprised of D' water Transfer these standards to abeled 20-mL viais. 2. In a 10mL vourmetric flask, prepare a sample that contains 1.00 mL mohash and 50% vv TISAB The solution will be quite foamy, so take care not to add the TISAB and Dil water too vigorously. You may also want to add the TISAB and some of the DI water prior to adding the mouthwash (be sure that you do not overshoot the mark, though). Mix well. Repeat for the other mouthwash sample. Transfer these samples to labeled 20-m vials 3. When all of your samples are prepared, add a small magnetic stir bar to the sample to be measured Put the vial onto strplate and carefully lower tuonde eectode the solton Record the potential (in mV). Remove the stir bar and wipe it dry with a Kimwlpe. Repeat for each standard and Prepare a calibration curve from your data (see page 313 of your textbook about how to do so) and use it to determine the concentration of your unknown and control samples. From these caiculated concentrations, determine the % wiv of fuoride in each sange not, that this reported as Neper 100 mL solution. You should also report the mg of NaF per 10 mL dose The waste generated from this lab can be safely washed down the drain. Data Determincd Table I of Solutions AB ( 50%) 0 rem Table 2: Data Determined pem 0 ppm 0 ppen 100 ppm 0 mV 5.3 mV 1 mV 18.0 mV 0 mV 74 mV

Show transcribed image text CHEM 319, QUANTITATIVE ANALYSIS LA8ORATORY EXERCISE à¸®6 QUANTIFYING FLUORIDE USING AN ION SELECTIME ELECTRODE PRE-LAD READING Read Harris pages 303-306 311-317 (on-selective electrodes) Lean how to prepare samples for analysis from dmicut to wark with starting materials Learn how to prepare calibration curves from ISE data EXPERIMENT OVERVIEW For this lab, you will determine the fuoride content in commercial mouthwashes using an ion selective electrode. This lab uses the direct potentiometry method, which assumes that matrix interferences are not a problem for determining the concentration of fuoride in toothpaste. To combat possible matrx problems, the total ionic strength adjustment buler (TISAB) solution used in the experiment contains 12 gand ensures that cations of meta's such as iron and copper in the sample will not complex the fuoride on. The TISAB will also adjust and stablize the lonic strength of the measured solutions lonic strengt can be a large factor affecting accuracy in ion selective electrode (ISE) measurements MATERIALS Total ionic strengh adjustment bulffer (TISAB) Fluoride stock solution (500 ppm wv) Two commercial mouthwashes (one control and one unknown) Fluoride lon selective electrode 10 mL volumetric fasks Sar bars 20-mL vials 1. Prepare five 10 mL standard solutions (2 ppm. 5 ppm, 20 ppm. 50 ppm, and 100 ppm)each containing 50%w/v ofthe TISAB andthe residual volumne comprised of D' water Transfer these standards to abeled 20-mL viais. 2. In a 10mL vourmetric flask, prepare a sample that contains 1.00 mL mohash and 50% vv TISAB The solution will be quite foamy, so take care not to add the TISAB and Dil water too vigorously. You may also want to add the TISAB and some of the DI water prior to adding the mouthwash (be sure that you do not overshoot the mark, though). Mix well. Repeat for the other mouthwash sample. Transfer these samples to labeled 20-m vials 3. When all of your samples are prepared, add a small magnetic stir bar to the sample to be measured Put the vial onto strplate and carefully lower tuonde eectode the solton Record the potential (in mV). Remove the stir bar and wipe it dry with a Kimwlpe. Repeat for each standard and Prepare a calibration curve from your data (see page 313 of your textbook about how to do so) and use it to determine the concentration of your unknown and control samples. From these caiculated concentrations, determine the % wiv of fuoride in each sange not, that this reported as Neper 100 mL solution. You should also report the mg of NaF per 10 mL dose The waste generated from this lab can be safely washed down the drain. Data Determincd Table I of Solutions AB ( 50%) 0 rem Table 2: Data Determined pem 0 ppm 0 ppen 100 ppm 0 mV 5.3 mV 1 mV 18.0 mV 0 mV 74 mV

Gather 2 pieces of square filter paper, the scissors, a pencil, and a ruler. DO NOT use a pen

or any form of ink. Create a strip of filter paper that measures 14 cm by 7 cm. See Figure 3.

Use the ruler to measure 14 cm across the edge of the paper. Use the pencil to draw a small

âxâ at 14 cm. On an adjacent edge of the paper, use the ruler to measure 7 cm up the edge

of the paper. Use the pencil to draw a small âxâ at 7 cm. Using the ruler as a straightedge,

lightly trace a rectangle that is approximately 14 cm by 7 cm. Use the scissors to cut out the

rectangle. Create two additional strips of paper.

Note:There should be enough filter paper to create a fourth 14 x 7 cm strip of paper if needed.

2.Gather the 25 mL graduated cylinder, 100 mL beaker, distilled water, and salt. Use the

graduated cylinder to add a total of 50 mL of distilled water to the beaker. Add a pinch of salt

to the beaker. Use the stirring rod to stir the solution until the salt has completely dissolved,

resulting in a salt solution of approximately 0.1% NaCl.

3.Gather 2 sheets of the filter paper â 14 x 7 cm from step 1.

a.Create a base line by drawing a thin horizontal line with a pencil (NOT a pen!)

across the paper, 10 mm (1 cm) from the bottom. The line should barely be visible.

b.With a pencil, draw 9 small cross lines along the horizontal line, 1.5 cm apart,

Experiment

Chromatography of Food Dyes

4.Repeat step 3 for the second piece of filter paper.

5.On Sheet 1, from left to right, use a pencil to lightly label each section between the cross lines

with the abbreviation for the six FD& C food colors from your experiment bag that will be

tested: B1, B2, R3, R40, Y5, and Y6.

6.Also on Sheet 1, after Y6, place the labels KG and KS to represent the Kool-

Grape and Kool-Aid

Â®Strawberry drink mixes to be tested.

7.On Sheet 2 from left to right, use a pencil to lightly label each section between the cross lines

with the abbreviation for the grocery store food coloring that will be tested: SR, SY, SG, and SB.

8.Also on Sheet 2, after SB, place the label âUKâ for unknown and then âMâ plus a letter for the

color of 4 different candies from your bag of M&Ms: such as; M-R (for M&MÂ® red), M-Y, M-B,M-G.

9.Set Sheet 2 aside and perform the following for Sheet 1. After you have completed the

experiment for Sheet 1, repeat for Sheet 2.

10.Put on your safety gloves and goggles.

11.For each dye on the sheet to be tested:

a.Use the scissors to cut open the pipets and place them in the 24-well plate, bulb

side down, using the well plate as a pipet holder.

b.Place a few drops of the dye in a well of the 24-well plate, as shown in Figure 4.

Dye drops and pipets in well

12.Once the paper is spotted with all the dyes, allow the spots to dry for a few minutes.

13.Form the spotted filter paper into a cylinder (colored spots on the inside) with the edges

touching, but NOT overlapped, and staple at the top and bottom as shown in Figure 7. (You

may want to use small pieces of tape on the outside to lightly hold the cylinder together

while you securely staple it. If so, remove the tape after stapling.) Set the cylinder aside for a

moment.

14.The salt water (~0.1% NaCl) you previously prepared will be your eluting solvent and a Petri

dish will be your elution chamber. Pour salt water into the clean and empty Petri dish to a

depth of about 1/4 cm. This is just enough to cover the bottom of the elution chamber.

15.Set your paper cylinder next to (not in) the Petri dish, with the spots at the bottom, and look

to make sure the solvent level is below the base line. If it is not, pour out a little solvent until

it is.The base line (and spots at the bottom of the chamber) must be above the solvent level

for this experiment to work.

16.Carefully place the paper cylinder into the eluting chamber, making sure not to touch the Petri

dish sides. See Figure 8. The solvent-front will travel up the paper rapidly at first and then will

slow down. Let the solvent-front rise, monitoring every few minutes. Immediately remove the

cylinder if any dye or the solvent front moves up higher than 2 cm from the top of the paper.

If all the solvent is soaked up before the front has time to move toward the top of the paper

carefully add a little more solvent to the Petri dish.

17.When the solvent-front has traveled up the filter paper, 2 cm from the top, remove the filter

paper cylinder from the chamber and immediately mark the top the solvent-front, on the dry

part of the paper, with a pencil. See Figure 9.

18.Allow the paper to dry, carefully remove the staples,

and draw an outline around each spot

using a pencil.

19.Take a photograph of your chromatogram after you have circled the spots.

Resize and insert the photograph of your chromatogram in Data Table 1of your

Lab Report Assistant

20.Use the ruler to measure the distance of the solvent front, in millimeters. Use Figure 1 in the

Background section as needed. Record the distance of the solvent front in Data Table 2 of your

Lab Report Assistant

For each of the dye spots on the filter paper chromatogram, measure and record to the

nearest millimeter the distance each of the spots has traveled up the solvent front. Start from

the original horizontal pencil line (base line) and measure to the top center of where the dye

stops in each column on the paper. See Figure 2 in the Background section as needed.

22.Calculate the Rf value for each spot and record in Data Table 2

23.Repeat steps 10 through 22 for the second sheet of filter paper. Record all data for this

chromatogram in Data Table 3 of your Lab Report Assistant

24. Compare the Rf values for the spots of the Kool-Aid Â®, unknown sample, store food colorings,and M&Ms Â®

, to those of the known FD&C food dyes, to determine which FD&C dyes are used in the Kool-AidÂ®, the grocery store food colorings, and in the M&Ms Â®.

25.Record the FD&C dyes present in each of the samples in Data Table 4 of your Lab ReportAssistant

26.Clean up all equipment and return to the lab kit for future use.

27.When you are finished uploading photos and data into your Lab Report Assistant, save your

file correctly and zip the file you can send it to your instructor as a smaller file.

Enter the results from chromatography filter paper Sheet 1 of your experiment in the following tables. If more than one colour is present in a sample, please indicate colour when referring to distance and Rf measurement.

Sheet 1: FD&C Food Colours

Colour	Blue 1	Blue 2	Red 3	Red 40	Yellow 5	Yellow 6	Solvent
Distance (mm)
Rf							--

Sheet 1: Drink Mixes

Substance	Kool-AidÂ® Grape	Kool-AidÂ® Strawberry	Solvent
Distance (mm)
Distance (mm)			--
Rf			--
Rf			--

Enter the results from chromatography filter paper Sheet 2 of your experiment in the following tables. Indicate the colours of M&Ms used in the experiment.

Sheet 2: Store Food Colours

Substance	Store Red	Store Yellow	Store Green	Store Blue	Solvent
Distance (mm)
Distance (mm)					--
Rf					--
Rf					--

Sheet 2: Candy Colours and Unknown

Substance	M&M	M&M	M&M	Unknown	Solvent
	Colour:	Colour:	Colour:
Distance (mm)
Distance (mm)					--
Distance (mm)					--
Rf					--
Rf					--
Rf					--

Answer the following questions based on your experimental results.

Show the calculation for the Rf value for Red40.

What FD&C colour(s) make up the unknown sample?

What FD&C colours make up the food colourings? State the brand used.
What FD&C colours make up the Kool-AidÂ® drinks and M&MsÂ®?

CHEM-115 Midterm: CHEM 115 Georgetown Exam1(2002)

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