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Slowinski Chemical Principles in the Lab 13e (Homework)

James Finch

Chemistry - College, section 1, Fall 2019

Instructor: Dr. Friendly

Current Score : 15.8 / 34

Due : Friday, February 1, 2030 00:00 EST

Last Saved : n/a Saving...  ()

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Question
Points
1 2 3 4 5 6 7 8 9 10
12/12 0/2 –/2 2/2 –/2 –/5 1/1 0.8/1 –/6 0/1
Total
15.8/34 (46.5%)

  • Instructions

    Engage your students and prepare them for success in your course with the student-friendly approach of Slowinski, Wolsey, and Rossi’s lab manual and WebAssign in Chemical Principles in the Laboratory, 13th edition. With the flexibility of WebAssign, you can remove barriers to learning and offer an engaging experience for all students.

    WebAssign provides a variety of question types that allow students to engage with the concepts covered in the course:
    • A PhET Simulation Tutorial (#1) uses a linked PhET simulation to provide opportunities for your students to engage with concepts outside of time spent in a physical lab space.
    • Concept Questions (#2-3) are used in pre-lab assignments that include questions and exercises specifically written to tie chemical concepts learned in lecture to the laboratory experiments.
    • Advanced Study Assignment Questions (#4-6) include sample questions, usually involving calculations, similar to those required in processing the data obtained in each experiment. Students who complete the ASA prior to lab should be well-positioned to work up the data they observe in the lab session.
    • LabSkills Modules (#7-10) prepare students for the lab experience virtually by focusing on lab technique, measurement and chemical reactivity through interactive simulations and auto graded quizzes.

Assignment Submission

For this assignment, you submit answers by question parts. The number of submissions remaining for each question part only changes if you submit or change the answer.

Assignment Scoring

Your last submission is used for your score.

1. 12/12 points  |  Previous Answers SlowChemLab13 SIM.1.001. My Notes
Question Part
Points
Submissions Used
1 2 3 4 5 6 7 8 9 10 11 12
1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1 1/1
2/100 1/100 1/100 1/100 1/100 1/100 1/100 1/100 2/100 1/100 1/100 1/100
Total
12/12
 
  • The PhET Simulation Tutorial uses a linked PhET simulation to provide opportunities for your students to engage with concepts outside of time spent in a physical lab space.

Beer's Law

Introduction
What if you were given an unknown solution and wanted to find out how much material was dissolved in that solution?
One method for determining the concentration of a solution involves finding its absorbance—by means of a transmittance measurement—using a spectrophotometer instrument.
This, in turn, will help you find the concentration using what is called "Beer's Law", which holds that the loss of light intensity is proportional to the concentration of a solution and path length.
Recall:
  • The concentration of a solution is a way to describe how much of a compound—the solute—is dissolved in a solvent.
  • Molar concentration or molarity is the number of moles of solute per liter of solution, symbolized as mol/L. The unit mol/L is also written as simply M.
Part 1 of 11
To learn how to use a spectrophotometer to measure the concentration of a solution, open the simulation "Beer's Law Lab" and select the "Beer's Law" option.
screenshot of the Beer's Law Lab simulation

Click to interact

(PhET Interactive Simulations by The University of Colorado are used under CC BY 2.0.)
The controls for this simulation are located at the bottom near the center.
  • Solution. (The default is "drink mix".)
  • Concentration. (The default is "100 mM".)
In this simulation, concentration is measured in units of millimoles per liter, symbolized as mM.
In case you need to reset the simulation, use the orange button with the circular arrow.
To begin, select "cobalt(II) nitrate" as the solution. Then, turn on the light source by clicking on its round, red button. Do not adjust any other values or settings at this time.
The transmittance of a sample tells you how much light passes through, or is transmitted, by a sample solution.
The absorbance of a sample tells you the opposite—how much light is absorbed by, or does not pass through, the sample.
What is the transmittance through the 100 mM cobalt(II) nitrate solution?
     Correct: Your answer is correct.
✓ Correct. This means 33.73% of the light can pass through the sample to the detector.
What is the absorbance through the 100 mM cobalt(II) nitrate solution?
     Correct: Your answer is correct.
✓ Correct. An absorbance value is unitless.
Part 2 of 11
You found the absorbance of the 100 mM cobalt(II) nitrate solution in Part 1.
Now adjust the concentration of the cobalt(II) nitrate solution to be 200 mM, but do not change any other settings.
How does the absorbance of the 200 mM solution compare to the absorbance of the 100 mM solution?
The absorbance of the 200 mM solution is double Correct: Your answer is correct. seenKey

double

 the absorbance of the 100 mM solution. ✓ Correct. The absorbance of the 200 mM solution is 0.94, and the absorbance of the 100 mM solution is 0.47.
Part 3 of 11
Now use the simulation to test your prediction.
What is the absorbance of a 400 mM solution of cobalt(II) nitrate?
     Correct: Your answer is correct.
✓ Correct. The absorbance of the 400 mM solution was higher than the absorbance of the 100 or 200 mM solutions.
Part 4 of 11
Consider your data for the absorbance of 100, 200, and 400 mM solutions of cobalt(II) nitrate.
How could you describe the relationship between the cobalt(II) nitrate concentration and the absorbance of light by the cobalt(II) nitrate solution?
As the cobalt(II) nitrate concentration increases, the absorbance of light increases Correct: Your answer is correct. seenKey

increases

 . ✓ Correct. The absorbance of the solution increased at a steady rate as the concentration was increased.
Part 5 of 11
Based on your results in Part 4, which equation could be used to represent how absorbance, A, depends on concentration of cobalt(II) nitrate, c? (Assume that k is a constant. We will explore this later.)
     Correct: Your answer is correct.
✓ Correct. The absorbance of the solution doubles each time the concentration doubles, which implies a linear relationship.
Part 6 of 11
In Part 5, you found the equation that represents the relationship between concentration and absorbance, where k is a constant.
However, what exactly is the constant k?
It is actually a combination of two variables, one of which depends on the pathlength of the light through the sample.
Set the simulation to measure absorbance on a 100 mM cobalt(II) nitrate solution.
Select the yellow, double-sided arrow and "pull" it towards the right, widening the sample container (called a cuvette).
What happens to the absorbance value as the cuvette width increases?
As the cuvette width increases, the absorbance of light increases Correct: Your answer is correct. seenKey

increases

 . ✓ Correct. The absorbance of the solution increased at a steady rate as the cuvette width was increased.
Part 7 of 11
The absorbance of a solution has a linear relationship with the concentration of the solution, as well as with the cuvette width of the sample container.
The wavelength of light also affects the absorbance of a solution.
So far, the light beam has looked green during the experiments on the cobalt(II) nitrate solution.
Note the "preset" wavelength value on the light source for the cobalt(II) nitrate solution. What is the "preset" wavelength (in nm) for the cobalt(II) nitrate solution?
     Correct: Your answer is correct.
✓ Correct. The preset wavelength for the cobalt(II) nitrate solution is 549 nm.
Part 8 of 11
You found the preset wavelength for the cobalt(II) nitrate solution in Part 7.
What happens if the wavelength differs from this preset value?
If not already so, set the simulation to measure absorbance on a 100 mM cobalt(II) nitrate solution.
Select "variable" instead of "preset" in the Wavelength box.
Using the slider on the color spectrum, adjust the wavelength of the light along the range of colors. Which statement best describes how the absorbance value relates to the wavelength of light?
     Correct: Your answer is correct.
✓ Correct. The preset wavelength for the cobalt(II) nitrate solution is 549 nm, because this wavelength was determined to be the wavelength of maximum absorbance for the cobalt(II) nitrate solution.
Part 9 of 11
In Part 8, you explored the relationship between the absorbance value of the cobalt(II) nitrate solution and the wavelength of the light in the light source.
How would the absorbance behave if the solution tested is something other than cobalt(II) nitrate?
In the simulation, choose nickel(II) chloride as the solution, using the dropdown.
Make sure the measurement is set to "Absorbance", that the light source is on, and that the Wavelength is set to "preset".
How does the wavelength of maximum absorbance of the nickel(II) chloride solution compare to the wavelength of maximum absorbance of the cobalt(II) nitrate solution?
The wavelength of maximum absorbance of the nickel(II) chloride solution is shorter than Correct: Your answer is correct. seenKey

shorter than

 the wavelength of maximum absorbance of the cobalt(II) nitrate solution. ✓ Correct. The wavelength of maximum absorbance of the nickel(II) chloride solution is 433 nm, which is shorter than the wavelength of maximum absorbance of the cobalt(II) nitrate solution, which was 549 nm.
Part 10 of 11
In Part 9, you compared the wavelength of maximum absorbance of the nickel(II) chloride solution to the wavelength of maximum absorbance of the cobalt(II) nitrate solution.
Why do you think the two solutions had a maximum absorbance of light at two different wavelengths of light?
To start answering this question, first think about the colors of light in the light source.
Did you notice anything about the colors of light at different wavelengths?
     Correct: Your answer is correct.
✓ Correct. The light at 433 nm is blue, and the light at 549 nm is green.
Part 11 of 11
This difference in the wavelengths and colors of light could be explained by the difference in colors of the solutions.
  • The red cobalt(II) nitrate solution absorbs the most light from the light source when the light is green.
  • The green nickel(II) chloride solution absorbs the most light from the light source when the light is blue.
If you test for the maximum absorbance wavelength of other solutions in the simulation, you would find that each solution has a unique wavelength of maximum absorbance.
Try it and see if you notice any patterns in what color light yields the maximum absorbance value for different solutions.
Based on your tests so far, do you think absorbance could be used to help identify an unknown solution?
     Correct: Your answer is correct.
✓ Correct. Because each compound has a unique molecular structure, it absorbs energy in unique ways. This means each compound in solution will have a unique wavelength of maximum absorbance, and absorbance can be used to help identify unknown solutions.
Conclusion: Beer's Law
You have completed this simulation.
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2. 0/2 points  |  Previous Answers SlowChemLab13 CQ.1.012. My Notes
Question Part
Points
Submissions Used
1 2
0/1 0/1
1/100 1/100
Total
0/2
 
  • Concept Questions (CQ) are used in pre-lab assignments that include questions and exercises specifically written to tie chemical concepts learned in lecture to the laboratory experiments.
(a)
How many grams of boron are present in 2.58 moles of boron tribromide?
WebAssign will check your answer for the correct number of significant figures. Incorrect: Your answer is incorrect. seenKey

27.9

 g
(b)
How many moles of bromine are present in 2.04 grams of boron tribromide?
WebAssign will check your answer for the correct number of significant figures. Incorrect: Your answer is incorrect. seenKey

0.0244

 moles


Solution or Explanation
The formula for boron tribromide is BBr3 and its molar mass is 250.522 g/mol.
(a)
To convert moles of BBr3 to grams of B, we proceed as follows.
First, multiply by moles of B per mole BBr3. Moles of BBr3 cancel out.
Then, multiply by grams of B per mole of B. Moles of B cancel out.
m(B) = 2.58 mol BBr3 ✕ 
1 mol B
1 mol BBr3
 ✕ 
10.81 g B
1 mol B
 
 = 27.890 g B ≅ 27.9 g B
(b)
To convert grams BBr3 to moles Br, we proceed as follows.
First multiply by moles of BBr3 per gram BBr3. Grams of BBr3 cancel out.
Then multiply by moles of Br per mole of BBr3. Moles of BBr3 cancel out.
n(Br) = 2.04 g BBr3 ✕ 
1 mol BBr3
250.522 g BBr3
 ✕ 
3 mol Br
1 mol BBr3
 = 0.024429 mol Br ≅ 0.0244 mol Br
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3. –/2 points SlowChemLab13 CQ.1.013. My Notes
Question Part
Points
Submissions Used
1 2
–/1 –/1
0/100 0/100
Total
–/2
 
  • Concept Questions (CQ) are used in pre-lab assignments that include questions and exercises specifically written to tie chemical concepts learned in lecture to the laboratory experiments.
Determine the molecular and empirical formulas for the substance shown in the ball-and-stick model below.
C: black
H: gray
Six black spheres form a ring. Each black sphere is connected to two gray spheres.
(a)
molecular formula

chemPad

Help

 
(b)
empirical formula

chemPad

Help

 
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4. 2/2 points  |  Previous Answers SlowChemLab13 1.ASA.001. My Notes
Question Part
Points
Submissions Used
1 2
1/1 1/1
1/100 1/100
Total
2/2
 
  • The Advance Study Assignments (ASA) include sample questions, usually involving calculations, similar to those required in processing the data obtained in each experiment. Students who complete the ASA prior to lab should be well-positioned to work up the data they observe in the lab session. This is question 1 of 3 that correlate with a single lab.
Many mass and volume measurements in chemistry are made by the method used below. This method is called "measuring by difference", and it is a very useful one.
A student obtained a clean, dry glass-stoppered flask. She weighed the flask and stopper on an analytical balance and found the total mass to be 45.020 g. She then filled the flask with water and obtained a mass for the full stoppered flask of 94.875 g.
From these data, and the fact that at the temperature of the laboratory the density of water was 0.9971 g/cm3, find the volume (in cm3) of the stoppered flask.
(a)
First we need to obtain the mass (in g) of the water in the flask. This is found by recognizing that the mass of a sample is equal to the sum of the masses of its parts.
For the filled and stoppered flask:
mass of filled stoppered flask = (mass of empty stoppered flask) + (mass of water)
So:
mass of water = (mass of filled flask) − (mass of empty flask)
 = WebAssign will check your answer for the correct number of significant figures. Correct: Your answer is correct. seenKey

49.855

 g
(b)
The density of a pure substance is equal to its mass divided by its volume:
density = 
mass
volume
So:
volume = 
mass
density
The volume of the flask is equal to the volume of the water it contains. Since we know the mass and density of the water, we can find its volume and that of the flask. Calculate the volume (in cm3) of the flask.
volume of flask = volume of water = 
mass of water (g)
density of water (g/cm3)
 = volume (cm3)
 = WebAssign will check your answer for the correct number of significant figures. Correct: Your answer is correct. seenKey

50.00

 cm3


Solution or Explanation
(a)
Calculate the mass of water in the flask.
mass of water = mass of filled flask − mass of empty flask
 = 94.875 g − 45.020 g = 49.85500 g ≅ 49.855 g
(b)
Find the volume of the stoppered flask.
volume of flask = 
mass of water
density of water
 = 
49.85500 g
0.9971 g/cm3
 = 50.0000 cm3 ≅ 50.00 cm3
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5. –/2 points SlowChemLab13 1.ASA.002. My Notes
Question Part
Points
Submissions Used
1 2
–/1 –/1
0/100 0/100
Total
–/2
 
  • The Advance Study Assignments (ASA) include sample questions, usually involving calculations, similar to those required in processing the data obtained in each experiment. Students who complete the ASA prior to lab should be well-positioned to work up the data they observe in the lab session. This is question 2 of 3 that correlate with a single lab.
Having obtained the volume of a flask (50.00 cm3), the student emptied the flask, dried it, and filled it with an unknown liquid whose density she wished to determine. The mass of the stoppered flask when completely filled with liquid was 85.173 g. The mass of the empty stoppered flask was 44.973 g.
Find the density of the liquid. (in g/cm3)
(a)
First we need to find the mass (in g) of the liquid by determining the difference.
mass of liquid = WebAssign will check your answer for the correct number of significant figures. g
(b)
The density of a pure substance is equal to its mass divided by its volume:
density = 
mass
volume
Since the volume of the liquid equals that of the flask, we know both the mass and volume of the liquid and can easily find its density. Calculate the density (in g/cm3) of the unknown liquid.
density of liquid = WebAssign will check your answer for the correct number of significant figures. g/cm3
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6. –/5 points SlowChemLab13 1.ASA.003. My Notes
Question Part
Points
Submissions Used
1 2 3 4 5
–/1 –/1 –/1 –/1 –/1
0/100 0/100 0/100 0/100 0/100
Total
–/5
 
  • The Advance Study Assignments (ASA) include sample questions, usually involving calculations, similar to those required in processing the data obtained in each experiment. Students who complete the ASA prior to lab should be well-positioned to work up the data they observe in the lab session. This is question 3 of 3 that correlate with a single lab.
Having obtained the volume of a flask (50.00 cm3), the student then emptied the flask and dried it. The mass of the empty stoppered flask was 44.711 g. To the empty flask she added pieces of a metal until the flask was about three-fourths full. She weighed the stoppered flask and its metal contents and found that the mass was 448.391 g. She then filled the flask with water, stoppered it, and obtained a total mass of 453.327 g for the flask, stopper, metal, and water.
Find the density of the metal. (in g/cm3)
(a)
To find the density of the metal we need to know its mass and volume. We can easily obtain its mass (in g) by the method of differences.
mass of metal = WebAssign will check your answer for the correct number of significant figures. g
(b)
To determine the volume of metal, we note that the volume of the flask must equal the volume of the metal plus the volume of water in the filled flask containing both metal and water. If we can find the volume of water, we can obtain the volume of metal by the method of differences. To obtain the volume of the water we first calculate its mass (in g), as follows.
mass of water = mass of (flask + stopper + metal + water)
    − mass of (flask + stopper + metal)
 = WebAssign will check your answer for the correct number of significant figures. g
The volume of water (in cm3) is found from its density (0.9979 g/cm3).
volume of water = 
mass of water
density of water
 
 = WebAssign will check your answer for the correct number of significant figures. cm3
(c)
From the volume of the water, we calculate the volume (in cm3) of metal, as follows.
volume of metal = (volume of flask) − (volume of water)
 = WebAssign will check your answer for the correct number of significant figures. cm3
From the mass and volume of metal, find the density (in g/cm3), using the following equation.
density = 
mass
volume
 
 = WebAssign will check your answer for the correct number of significant figures. g/cm3
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7. 1/1 points  |  Previous Answers SlowChemLab13 LS.1.002. My Notes
Question Part
Points
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1
1/1
1/100
Total
1/1
 
  • LabSkills modules prepare students for the lab experience virtually by focusing on lab technique, measurement and chemical reactivity through interactive simulations and auto graded quizzes. Detailed and instant feedback give students the help they need when they need it. This is an example of an introductory safety question.
Review the following material and then answer the question that appears below.
LabSkills
Lab Safety
  • Unauthorized experiments should never be performed in the laboratory.
  • Never work in the laboratory alone.
  • Eating and drinking is strictly prohibited. This includes chewing gum. If you ingest (or think you have ingested) any chemicals, seek immediate medical help, and show the container or label to a staff member.
  • Smoking is forbidden. This includes vaping devices and electronic cigarettes. Many chemicals found in the lab are highly flammable.
  • Keep long hair tied back.
  • Long accessories should not be worn; neckties and necklaces might get contaminated or caught in equipment.
  • Cell phones, music players, etc. must be switched off when entering the laboratory. Anything that interferes with your ability to hear what is going on in the laboratory is a potential hazard.
  • After reading all warnings and recommendations, use chemicals carefully and in a fume hood whenever possible.
  • Dispose of solvents in the correct container. Immediately return any chemicals you have used.
  • Keep your work area and common areas tidy and clean at all times. Clean up any spills, including water, on the floor or on your bench.
  • Wash your hands before leaving the lab to remove trace amounts of chemicals that you may have come into contact with.
  • Sign in and sign out on the laboratory attendance sheet.
  • Assume you are the only safe worker in the laboratory. Work defensively!
  • If you feel unwell during the lab and need to leave, you should immediately speak to a staff member.
Question
Under which circumstances is it appropriate to work in the laboratory alone?
     Correct: Your answer is correct.


Solution or Explanation
It is never safe to work in a laboratory alone.
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8. 0.8/1 points  |  Previous Answers SlowChemLab13 LS.4.005. My Notes
Question Part
Points
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1
0.8/1
1/100
Total
0.8/1
 
  • LabSkills modules prepare students for the lab experience virtually by focusing on lab technique, measurement and chemical reactivity through interactive simulations and auto graded quizzes. Detailed and instant feedback give students the help they need when they need it. This example provides the student with a video and asks a question corresponding to the concepts in the video.
Review the following material and then answer the question that appears below.
A bottle containing a reagent was weighed to show a mass of 56.2601 g.
Some material was carefully transferred to a reaction flask, and the bottle reweighed to show a mass of 54.9041 g.
What mass (in g) of the material was transferred to the flask?
WebAssign will check your answer for the correct number of significant figures. g
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9. –/6 points SlowChemLab13 LS.14.001. My Notes
Question Part
Points
Submissions Used
1 2 3 4 5 6
–/1 –/1 –/1 –/1 –/1 –/1
0/100 0/100 0/100 0/100 0/100 0/100
Total
–/6
 
  • LabSkills modules prepare students for the lab experience virtually by focusing on lab technique, measurement and chemical reactivity through interactive simulations and auto graded quizzes. Detailed and instant feedback give students the help they need when they need it. This is an example of a step-by-step question designed to take the student through a sample laboratory scenario.
This question has several parts that must be completed sequentially. If you skip a part of the question, you will not receive any points for the skipped part, and you will not be able to come back to the skipped part.
Lab Skills Exercise

Mole Calculations

This exercise is designed to allow you to practice finding how many moles of a pure inorganic solid are present in a sample of known mass.
A pure sample of solid potassium dichromate, K2Cr2O7, was found to have a mass of 7.55 g.
Calculate the moles of potassium dichromate in this sample.
  • In this exercise, the known values are:
    • mass,
    • compound formula, and
    • molar masses of the elements that make up the compound.
    This is enough information to determine the moles of solid present.
    • Recall the definition of molar mass.
      molar mass (g/mol) = 
      mass of compound (g)
      moles of compound (mol)
      Rearrange the equation to solve for moles of compound.
    • From:
      • the compound formula (which is given)
      • the molar masses of the elements that make up the compound (which are known)
    • From:
      • the mass of the compound (which is given)
      • the molar mass of the compound (which you can calculate)
      • the relationship between moles, mass, and molar mass (which is known)
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10. 0/1 points  |  Previous Answers SlowChemLab13 LS.33.001. My Notes
Question Part
Points
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1
0/1
1/100
Total
0/1
 
  • LabSkills modules prepare students for the lab experience virtually by focusing on lab technique, measurement and chemical reactivity through interactive simulations and auto graded quizzes. Detailed and instant feedback give students the help they need when they need it. This example gives the students an interactive guide and asks the student a question based on the information in the guide.
Review the following material and then answer the question that appears below.
What are gas traps commonly used for? (Select all that apply.)
Incorrect: Your answer is incorrect.



Solution or Explanation
Gas traps are used to prevent the release of harmful or odorous gases from the reaction. They are not used to prevent a reaction from overheating or to add gases into reactions.
In summary, the gas traps can be used:
  • to prevent inhalation of harmful gases
  • to stop the release of toxic gases into the atmosphere
  • to avoid the release of unpleasant odors
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