CHEM 322 Midterm: CHEM 325 Midterm 1 2005

35 views4 pages

turquoisegnu128

9 Jan 2019

School

Department

Course

Professor

For unlimited access to Study Guides, a Grade+ subscription is required.

Document Summary

Midterm 1 october 12, 2005: a lake sample contains 2. 5 ppb of 3,3",4,4" tetrachlorobiphenyl (bz 77). One liter of this water is passed through an organic resin and 100% of the organic compounds are isolated on this resin. This resin is then extracted with 50 ml of pentane and all of the organics are transferred to the pentane. Isooctane is added to the pentane solution and all of the pentane evaporated. C) you are required to make an external calibration curve to measure the bz 77 concentrations in similar water systems using the method outlined above. 1000 ppm and directed to make up 5 concentrations of bz 77 in 10 ml volumetric flasks. Select appropriate concentrations and describe how you would make these solutions. (make up your external calibration solutions in isooctane) Name: _____________________: a series of analysis were performed on single sample. Four measurements were made and concentrations determined using an external calibration curve.

Related Questions

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

I need help for my lab report please. It's only a-e Questions for study that I need help with, so any help or advice will be greatly appreciated! Underneath is more info on the lab if needed. Thank you!

Question for Study

1. A student performed this lab exercise, generating the following data:

Mass of H5IO6 used: 1.2320 g

Volume of thiosulfate used in blank titration: 47.93 mL

Volume of thiosulfate used in the unknown titration: 39.23 mL

a. What is the concentration of the sodium thiosulfate solution?

b. How many mmol of I3 â were present in the blank titration?

c. How many mmol of I3 â were present in the unknown titration?

d. How many mmol of glycol were present in the unknown titration?

e. What mass of ethylene glycol should be reported?

Introduction

The chemical analysis of organic compounds often presents major experimental difficulties. An accurate analysis depends upon the sample undergoing a single, well-defined reaction which quickly goes to completion. Often, organic compounds undergo several different reactions at the same time, and reaction rates are sometimes quite slow.

A functional-group analysis is one in which a particular grouping of atoms in a compound is made to react in a specific well-defined way with a particular reagent.1 In this experiment use is made of the reaction between an oxidizing reagent and an organic compound with the functional group COH-COH.

Analysis of Ethylene Glycol

Ethylene glycol reacts with periodate ion to form formaldehyde and iodate:

+ ð¼ð4 â â 2 ð»2ð¶ð +ð¼ð3 â + ð»2ð (8-1)

This oxidation-reduction reaction will proceed to completion with negligible side reactions under the appropriate set of conditions. The reaction is slow, but increases with increasing concentration of periodate. Here a known, fixed amount of periodate in excess of that needed to completely react with the glycol is added to the unknown. After the glycol has reacted, an excess of iodide is added to the solution. The iodide reacts with unreacted periodate according to:

ð¼ð4 â + 11 ð¼ â + 8 ð» + â 4 ð¼3 â +4 ð»2ð (8-2)

The iodide also reacts with the iodate produced in reaction 8-1 according to:

ð¼ð3 â + 8 ð¼ â + 6 ð» + â 3 ð¼3 â + 3 ð»2ð (8-3)

The triiodide produced in these reactions is then determined by titration with thiosulfate:

ð¼3 â +2 ð2ð3 2â â 3 ð¼ â + ð4ð6 2â (8-4)

To find the glycol content, a blank solution containing the same fixed amount of periodate but no glycol is treated similarly. The difference in the number of moles of ð¼3 â produced in the blank solution, and that produced in the sample solution, is equal to the number of moles of glycol in the sample solution.

Procedure

1. Prepare a solution from your unknown: a. Your unknown may have recently been refrigerated â make sure it is at room temperature before use. b. Transfer the vial contents quantitatively to a 250 mL volumetric flask. c. Dilute to volume with water and mix well.

2. Prepare a Periodic Acid standard solution (pronounced âpurr-eye-oh-dic acidâ): a. Weigh out 1.16-1.24 g of H5IO6 on an analytical balance. Periodic acid is very corrosive â to your skin and to metals. Do not spill any on the analytical balances. b. Quantitatively transfer the solid to a 100 mL volumetric flask, and dilute to volume with water.

3. Prepare a sodium thiosulfate solution: a. Weigh ~11.2 g of sodium thiosulfate pentahydrate. b. Transfer the solid to a 1L Pyrex bottle and dilute to 500 mL to produce an approximately 0.09 M solution. c. Add 0.10 g Na2CO3 and swirl to mix well.

4. Prepare a ~0.5 M solution of sulfuric acid: a. In a beaker (250 or 400 mL), combine 25 mL of 3 M sulfuric acid and 125 mL of water. Mix. Remember: âAcid Into Waterâ. What glassware is appropriate to measure these volumes?

5. Prepare samples for titration: a. Pipet 20 mL of your diluted unknown and 10 mL of the periodic acid solution into a 250 mL conical flask and swirl to mix. b. Wait a minimum of 45 minutes to allow complete reaction before titrating. Do the blank titrations while you wait! c. Prepare a total of 3 samples in this way.

6. Perform the sample titrations: a. Add ~1.5 g of KI to your conical flask and swirl to dissolve. b. Add 10 mL of your 0.5 M sulfuric acid (use a graduated cylinder). c. Titrate from a dark red initial colour to the first change to yellow. d. Add 2.0 mL of thiodene indicator solution. The solution will become a dark grey/violet colour. e. Finish the titration (fractional drops) to a sharp disappearance of the violet colour. 7. Perform the blank titrations: a. Pipet 10 mL of periodic acid solution into a 250 mL conical flask. b. Add 20 mL of water with a graduated cylinder. c. Add reagents and perform the titration as in Step 6 above. Calculations Report the total mass (in mg) of ethylene glycol in your unknown.

THIS IS A LAB REPORT THAT I NEED HELP WITH I NEED HELP WITH ANSWERING THE POST LAB QUESITON THAT IS ALL THE WAY IN THE BOTTOM PLEASE HELP ME ANSWER THE POST LAB QUESTIONS THANK YOU! THE PRE LAB I HAVE ALREADY DONE BTW!

Determination of Cobalt (II) Chloride

by UV/VIS Spectroscopy

Introduction

The absorption of specific quantities of electromagnetic (light) radiation by an element or compound allows electrons to move from lower energy level to a higher energy level. We say that the energy levels are quantized. Electrons, returning to lower energy levels, will release energy within the electromagnetic spectrum. The wavelengths may be in the ultraviolet, visible, or infra red regions of the spectrum. For cobalt (II) chloride, the compound of study, the visible region, of the spectrum will be addressed.

By knowing the wavelength (l) or frequency (n) of radiation, one may determine the energy of the transition. Relationship between energy, wavelength and frequency are:

c= ln and E= hn or E= hc/l

The light radiation absorbed in a solution of this salt is proportional to its concentration through a relationship provided by the Beer-Lambert Law:

A = kC

where A= absorbance, k is Beerâs Law constant, and C is the molar concentration in solution.

The absorbance (A), a unit-less number is dependant on the quantity of light energy absorbed and transmitted by the solution through the following equation:

A= -log T or A = 2-log %T

where T= transmittance= I/I⁰ where I is the absorbed light and I⁰ is the impinging light source.

Purpose

The purpose of this laboratory experiment is to practice, learn and carefully prepare molar solutions to investigate the relationship of concentration and spectrophotometer response. A 0.150 M solution of cobalt (II) chloride will be provided. You will prepare diluted solutions through the serial dilution method, measure the transmittance and calculate the absorbance values. You will prepare a Beerâs law graph of data; molar concentration vs. absorbance. Then determine Beerâs law constant using Microsoft Excel program.

You will also be given a concentrated sample of cobalt (II) chloride of unknown concentration and you must determine the appropriate dilution to prepare and thereafter determine the unknown concentration.

Procedure

In order to carry out this analysis procedure, it will be necessary to determine the wavelength of transition. Recall, that one specific energy maximum exists for each transition. We will study the transition in the range of 400- 600 nanometers (nm). This is the visible region of the spectrum.

Step 1. Prepare the following solution concentrations using the 0.150 M cobalt (II) chloride stock solution, 18 mm x 150 mm test tubes and Mohr pipets.

TABLE 1

Solution No.	0.150 M CoCl₂ (mL)	Volume water (mL)
1	5.0	0.0
2	4.0	1.0
3	3.5	1.5
4	3.0	2.0
5	2.5	2.5
6	2.0	3.0
7	1.0	4.0

Step 2. Carefully place a cork or rubber stopper over each solution and mix the contents.

Step 3. Measure the transmittance of a 0.150M solution between 400 nm and 600 nm at 25 nm intervals.

To accomplish this, follow these steps:

Caution: instruments are delicate. If you are uncertain about instrument operation, ask your instructor for assistance. (Instructions on instrument operation- see next page.)

SPECTRONIC is a registered trademark of Spectronic Instruments, Inc.

Instrument operation- edited version of product ^*Operatorâs Manual

Transmittance and Absorbance

1. Turn on the instrument by turning the Power Switch (10) clockwise. Allow the spectro-photometer to warm up for at least 15 minutes to stabilize.

2. After the warm-up period, set the desired wavelength with the Wavelength Control Knob.

3. Set the filter lever to the appropriate position for the selected wavelength (not required for SPECTRONICÂ® 20D).

4. Adjust the display to 0%T with the Zero Control (10). Make sure that the sample compartment is empty and the cover is closed.

5. Set the display mode to TRANSMITTANCE by pressing the MODE control key until the appropriate LED is lit.

6. Fill a clean cell with water and wipe the cell with a tissue (Kimwipe^TM) to remove liquid droplets, dust and fingerprints.

7. Place the cell in the sample compartment and align the guide mark on the cell with the guide mark at the front of the sample compartment. Press the cell firmly into the sample compartment and close the lid.

8. Carefully adjust the display to 100%T with the Transmittance/Absorbance Control (9). Move the knob slowly as you approach 100%T.

9. Remove the cell from the sample compartment and empty the water.

10. Rinse the cell twice with small volumes of the solution to be measured and fill it with the solution.

11. Wipe the cell with a tissue and insert the cell into the sample compartment. Align the guide marks and close the lid.

12. Read the appropriate value (%T) from the display.

13. Remove the cell from the sample compartment and repeat steps 10 through 12 for any remaining sample solutions.

14. When all measurements are completed, turn off the spectrophotometer by turning the Power Switch counterclockwise until it clicks.

Step 4. Using solution no. 1, follow the directions for instrument operation and record (%) transmittance values for each wavelength in Table 2.

Remember to reset the instrument to 100% for each wavelength investigated.

DO NOT DISCARD THIS SOLUTION,

Step 5. The wavelength that gives the largest absorbance value will provide the greatest sensitivity to concentration change. Generate an Excel graph of wavelength (x) vs. absorbance (y) using these values. At zero absorbance, there isnât any CoCl₂ so donât forget to include the (0,0) data point. Connect your data points with a smooth curve. This is the absorption spectrum of aqueous CoCl₂. Submit this with your lab report.

Step 6. Reset your spectrometer using this wavelength (step 5), and measure this solution and the other six solutions listed in Table 1, and record your % transmittance values in Table 3.

TABLE 2

Wavelength (nm)	% Transmittance	Absorbance
400
425
450
475
500
525
550
575
600

MAXIMUM ABSORBANCE IS LOCATED AT ________________nm.

TABLE 3 -Results measured at ______nm.

Test tube No.	% Transmittance	Absorbance	Molarity(M)
1
2
3
4
5
6
7

Step 7. Plot a graph of Molarity (M) vs. Absorbance for all seven solutions using Excel plotting techniques. This is called a calibration curve, whereby one establishes a measured response to a known solution concentration. Determine the slope of the line and include the linear equation of fit, and the correlation coefficient.

Recall the relationship A = kC or y = mx + b; where b is the (0,0) data point

Then: k = A/C

Step 8. The unknown solution to be analyzed is more concentrated than any of the standard solution concentrations that were measured to prepare the calibration curve.

Points to consider:

You must achieve a dilution such that the absorbance is within the absorbance range of the standards that were previously measured.

By using serial dilutions, will multiply many errors; thus it is best to obtain a dilution is one-step if possible.

Consider reducing the concentration by Â¾, or by Â½, and by Â¼ or to 0.10 of the original concentration and test the solution to see if the absorbance response is within range. You may also consider using the dilutions in Table 1. Once this is determined, proceed to the next step. Complete the dilution table for the diluted concentrations you prepared:

Trial	mL of unknown	mL of water	(%T)	A
1
2
3

Step 9. Using the desired dilutions, determined in step 8, measure two of the diluted solutions and record the measured transmittances in Table 4.

UNKNOWN NUMBER __________

TABLE 4

Diluted concentration (M)	Transmittance (%T)	Absorbance (A)

Calculation of absorbance, for diluted Unknown solution:

Step 10. Determine the concentration of the diluted solution using the linear equation of fit, knowing the absorbance and k, the slope of the line.

C = A/ k

Step 11: Determine the concentration in your original Unknown solution. Show your

back-calculation below to support your final answer to this experiment.

Calculations:

Unknown Solution No. ________ Concentration: ___________M

Prelab Questions

1. Consider a solution of 0.400M Co(NO₃)₂ provided by your lab instructor.

You are required to make the following dilute concentrations:

0.160M and 0.240M solutions. You are provided the following glassware: 5.0 mL Mohr pipet and 18 mm x 150 mm test tubes. Describe how you would prepare each solution, and support your description with your calculations. (Recall (M_c x V_c = M_d x V_d) where M_c is the molarity of the concentrated solution, V_c is the volume of the concentrated solution, M_d is the molarity of the dilute solution, and Vd is the volume of the diluted solution.)

Given 0.400 M Co(NO3)2 solution.

Lets say we pipette out 5 mL of this solution and dilute it to get 0.160 M solution. Then

Using, Mc x Vc = Md x Vd

0.400 x 5 = 0.160 x Vd or Vd= (0.400 x 5)/0.160 = 12.5 mL

Thus we need to add 7.5mL distilled water to 5 mL of cobalt nitrate. Since we are only provided with a 5 mL pipette, we can only measure out volumes in multiple of 5.

thus pipette out (5 x 2) 10 mL of cobalt nitrate solution in the test tube and dilute it by addition of (7.5 x2) 15 mL of distilled water.

Again for preparing 0.240 M solution

Lets say we pipette out 5 mL of this solution and dilute it to get 0.160 M solution. Then

Using, Mc x Vc = Md x Vd

0.400 x 5 = 0.240 x Vd or Vd= (0.400 x 5)/0.240 = 8.33 mL

Thus we need to add 3.33mL distilled water to 5 mL of cobalt nitrate. Again taking volumes only in multiples of 5, pipette out (5 x 3) 15 mL of cobalt nitrate solution in the test tube and dilute it by addition of (3.33 x3) 10 mL of distilled water.

2. In your own words, explain, in detail, what you will be learning during this lab. Address the chemical principles and, laboratory skills, in your answer.

Post - Lab Questions:

a) Letâs say, for a given concentration of salt solution, the maximum response at a wavelength maximum of 485nm, is 0.750. If an unknown solution is analyzed at a longer or shorter wavelength would the investigator obtain the same concentration for the Unknown solution? Explain why.

b) List all possible sources of errors that may result in this experiment.

CHEM 322 Midterm: CHEM 325 Midterm 1 2005

Document Summary

Get access

Related textbook solutions

Chemistry: Structure and Properties

Basic Chemistry

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Principles of Chemistry Molecular Approach

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

Related Documents

CHEM 322 Final: CHEM 325 Final Exam 2005

CHEM 322 Study Guide - Midterm Guide: Atomic Spectroscopy, Reagent, Spectroscopy

CHEM 322 Final: CHEM 326 Final Exam 2005

Related Questions