CHEM 351 Study Guide - Final Guide: Mull, Stereoisomerism, Lead

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turquoisegnu128

9 Jan 2019

School

University of Calgary

Department

Chemistry

Course

CHEM 351

Professor

All

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Document Summary

Enter version number 1 on the computer answer sheet. The examination consists of parts 1 - 9, each of which should be attempted. Note that some parts provide you with a choice of questions, i. e. answer 4 out of 5. These will be graded in numerical order until the required number have been completed, regardless of whether they are right or wrong. Parts 1 - 5 will be computer graded, and parts 6 - 9 are to be answered in the answer booklet provided. Parts 1 - 5 consist of a series of multiple choice questions numbered. 1 - 40, which are to be answered on your computer answer sheet. Indicate your answer by blackening out the appropriate space, a, b, c, d or e on the answer sheet (this must be completed within the 3hrs). Use a pencil only not ink to completely fill the circle(s).

Related Questions

Chromatography: Separating Mixtures

Introduction:

Magic marker inks are often mixtures of several compounds. Paper chromatography is a common method of separating various components of a mixture. After separation, you can observe the different colors that make up a particular color of magic marker ink.

You can also calculate a ratio Rf, which compares how far each compound traveled to how far each solvent (substance that dissolves another substance) traveled during the experiment.

Rf = Ds/Df

Ds = Distance traveled by the compound

Df = Distance traveled by the solvent

Materials:

coffee filter, tape, isopropyl alcohol (rubbing alcohol), water, 3 different color magic markers (not permanent); 3 identical tall, narrow drinking glasses; metric ruler, 3 pencils

Pre-lab Questions:

List one extensive and one intensive property of marker ink.

Intensive: Amount Doesn't Matter

Extensive: Amount Matters

An extensive property of marker ink would be volume or ink.

An intensive property of marker ink would be the color of ink.

Define mixture.

A combination of two or more substances that are not chemically combine with one another.

Is tap water a heterogeneous or homogenous mixture? Explain your answer.

Tap water is a homogeneous mixture. I think this because I can see that it has uniform. It doesnât contain any different molecules as well.

Is isopropyl alcohol (rubbing alcohol) a heterogeneous or homogenous mixture? Explain your answer.

I believe rubbing alcohol is a homogeneous mixture. I think this because I can physically see that it has uniform. It also stays in the same phase.

Procedure:

1. Cut 3 strips of coffee filter. Be sure that the strips are much narrower and slightly taller than the drinking glasses.

2. In the center the strips, about 3 cm from one end, place a dot of the marker to be tested. The dots should be about 0.2 cm in diameter and dark enough to be clearly visible.

3. Place about 2 cm of water in each glass.

4. Tape the unmarked end of each strip to the center of a pencil so that the strip hangs down when the pencil is held horizontally.

5. Carefully insert the strips into the glasses, dotted end down. The dot must be above the water, and the sides of the coffee filters cannot touch the sides of the glasses.

6. Let the setup stand for 20 minutes. Follow procedure 8 as your set up stands.

7. Record your observations after 20 minutes in the table below. Measure Df (in cm) for the solvent. Measure the Ds (in cm) for each color that you see on the coffee filter (there may not be three). Calculate the Rf for each color using the equation in the Introduction section.

8. Repeat steps 1â7, except place about 2 cm of isopropyl alcohol (rubbing alcohol) in each glass instead of water.

9. Clean up your work area.

Solvent: isopropyl alcohol (rubbing alcohol)

5. What evidence is there that marker ink is a mixture?

The marker ink is a mixture. The evidence is when the marker ink separated.

6. Each compound in the marker ink is represented by a color. Did one compound travel farther than the others? Explain why you think that this is the case.

Yes, I found out that the darker of the three colors traveled further.

7. Did the compounds travel farther in the water or the isopropyl alcohol (rubbing alcohol)? Explain why you think that this is the case.

The compounds traveled faster in the water than the rubbing alcohol. I think the reason why is because water is smaller on a molecular level versus rubbing alcohol. So it is easier for the dyes to separate.

8. How could you improve upon the accuracy of your Rf measurements?

I feel that accuracy could be improved if we changed the scale measurement to millimeters (mm) instead of cm (centimeters).

Water traveled faster than the rubbing alcohol. I personally think it has to do with something like the size of the molecule like the smaller the molecule the easier it is.

please help me answer some science questions:

Question 1: Choose all answers that correctly complete the following statement:

Science is...

Question 1 options:

A)	a set of careful steps followed in order by people in lab coats.

B)	just a collection of facts.

C)	a process of learning about the natural world.

D)	unchanging and static - once we know a scientific fact it does not change.

E)	a method that can answer any question.

F)	testing ideas with evidence.

Question 2 : "What is the meaning of life?" is a question that cannot be answered by science because

Question 2 options:

A)	it is not an interesting enough question for scientists.

B)	it involves collaboration with others to fully answer.

C)	it deals with supernatural explanations.

D)	it only has one answer.

Question 3 : Ignaz Semmelweis wanted to explain the high rates childbed fever mortality in his hospital in the 1800s. How did he use science?

Question 3 options:

A)	He wore a lab coat while in the maternity ward. He did not wear a lab coat in the rest of the hospital.

B)	He tested the idea that doctors caused the deaths by comparing mortality rates of patients treated by doctors that disinfected their hands (in between patients) with the mortality rates of patients that had dirty-handed doctors.

C)	He read a scientific journal about bacterial causes of childbed fever.

D)	He changed birthing procedures so that women gave birth on their sides and were assisted by doctors that disinfected their hands.

Question 4 : When determining which hypothesis or model to accept, scientists should

Question 4 options:

A)	choose the most popular explanation.

B)	choose the hypothesis supported by evidence.

C)	go with their favorite hypothesis (as long as it's still shiny).

D)	support the most recent hypothesis to be proposed as a plausible explanation.

Question 5: What happens when new evidence does not support a current scientific hypothesis (or current understanding of a natural phenomenon)?

Choose all that are correct.

Question 5 options:

A)	We should re-evaluate the current understanding and possibly reject past ideas based on the new evidence.

B)	The scientific community labels the scientist that collected the evidence as an unreliable quack.

C)	Scientists throw out the new evidence since obviously the experimental design must be flawed.

D)	Scientists should test the idea in a novel way (inspire new ideas) to determine if the new evidence is consistent with a new understanding.

Question 6: To gain entrance to the Science club, you should:

Question 6 options:

A)	fabricate your data often to support your favorite hypothesis.

B)	take all the credit for yourself.

C)	check all the boxes on the science checklist. If you miss even one, you're denied your scientist ID card.

D)	behave scientifically (preferably in a lab coat).

Question 7 : Choose all the answers that correctly complete the following statement:

Scientists interact with the scientific community by...

Question 7 options:

A)	speaking at conferences.

B)	locking themselves in ivory towers.

C)	being inspired by other scientists and testing their ideas in new and novel ways.

D)	only listening to NPR (National Public Radio) on Science Fridays.

E)	publishing in science journals.

Question 8: Which of the following questions CANNOT be answered using the scientific method?

Question 8 options:

A)	How does migration affect the reproductive success of monarch butterflies?

B)	Should local communities invest money in sustainable farming practices instead of new infrastructure (e.g., roads and bridges)?

C)	How does coastal development affect wetland biodiversity (number and types of organisms present)?

D)	Is water a toxic substance?

E)	Do pesticides cause developmental changes in frogs?

Question 9 : Choose all of the following answers that correctly completes the following statement:

Representing the scientific method in a linear, cookbook sequence:

Question 9 options:

A)	incorporates the important concept of testing ideas with evidence

B)	does not capture how science really works.

C)	is too simplified.

D)	incorrectly implies that there is an endpoint to science. (If the scientific method is a simple progression, once a valid conclusion is reached, science is done!)

PLEASE HELP ME ANSWER THE POST LAB QUESTIONS. I did THE PRE LAB. I ALSO FILLED in the tables.

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 Switchcounterclockwise 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	88.3	0.055
425	73.7	0.132
450	43.6	0.362
475	23.8	0.623
500	15.7	0.804
525	16.0	0.797
550	38.9	0.410
575	73.0	0.37
600	85.3	0.069

MAXIMUM ABSORBANCE IS LOCATED AT __________500______nm.

TABLE 3 -Results measured at _500_____nm.

Test tube No.	% Transmittance	Absorbance	Molarity(M)
1	15.8	0.802
2	22.8	0.643
3	27.4	0.562
4	33.1	0.480
5	40.2	0.396
6	47.6	0.323
7	69.3	0.159

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			51.9	0.284
2			70.7	0.151
3			79.3	0.101

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 _____B_____

TABLE 4

Diluted concentration (M)	Transmittance (%T)	Absorbance (A)
Pure unknown B	8.7	1.062
1 mL of unknown in 1 mL of water	29.5	0.531

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:

If needed I did a graph slope and got y= 0.1896x

R^2=0.9951

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 351 Study Guide - Final Guide: Mull, Stereoisomerism, Lead

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