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Harris - Quantitative Chemical Analysis 9/e (Homework)

James Finch

Chemistry - College, section 1, Fall 2019

Instructor: Dr. Friendly

Current Score : 20 / 20

Due : Wednesday, September 25, 2019 07:40 EDT

Last Saved : n/a Saving...  ()

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20/20 (100.0%)

  • Instructions

    Dan Harris's 9th edition of Quantitative Chemical Analysis, published by W. H. Freeman, provides a sound physical understanding of the principles of analytical chemistry and their applications in the disciplines. The WebAssign component for this text engages students with an interactive eBook, formatting of chemical symbols with the chemPad tool, and structure drawing with the MarvinSketch drawing tool.

    Question 1 shows a numeric question, highlighting that uncertainty can be tracked and graded as well.

    Question 2 shows our chemPad tool, which allows formatting of chemical symbols, such as this equilibrium reaction.

    Question 3 shows how several multiple-choice options can be combined into a single question that makes guessing much more difficult.

    Question 4 shows structure drawing with our MarvinSketch drawing tool, which at this level can include radicals, charged species, and ionic pairs as shown here.

    Question 5 shows a combination of multiple-choice and multiple-select questions, allowing for the second portion to test the reasoning behind the initial answer.

    Question 6 shows randomization of numbers and uncertainty (highlighted in red) in a numeric question.

    Question 7 shows that numbers and uncertainty can be represented in scientific notation where appropriate.

    View the complete list of WebAssign questions available for this textbook.

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. –/2 points HarrisChem9 3.P.021. My Notes
Question Part
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–/2
 
Express the molecular mass (± uncertainty) of C17H19NO3 with the correct number of significant figures.
WebAssign will check your answer for the correct number of significant figures.(No Response) seenKey

285.34

 ± WebAssign will check your answer for the correct number of significant figures.(No Response) seenKey

0.02

 g/mol

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2. –/1 points HarrisChem9 6.P.034. My Notes
Question Part
Points
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1
–/1
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–/1
 
Write the autoprotolysis reaction of H3N.

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2 H3N  ⇌  H2N- + H4N+

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3. –/4 points HarrisChem9 3.P.010. My Notes
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0/100 0/100 0/100 0/100
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–/4
 
Explain the difference between systematic and random error.
(No Response) seenKey

Systematic

 error is always above or always below the "true" value if you make replicate measurements. In principle, you can find the source of this error (No Response) seenKey

and you can eliminate it

 in a better experiment so the measured mean equals the true mean. (No Response) seenKey

Random

 error is equally likely to be positive or negative and cannot be eliminated. However, (No Response) seenKey

random

 error can be reduced in a better experiment.

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4. –/1 points HarrisChem9 6.P.032. My Notes
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1
–/1
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–/1
 
Use electron dot structures to show why tetramethylammonium hydroxide, (CH3)4N +OH −, is an ionic compound. That is, show why hydroxide is not covalently bound to the rest of the molecule. (Assign lone pairs, radical electrons, and atomic charges where appropriate.)
(No Response)
Marvin JS

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5. –/2 points HarrisChem9 3.P.011. My Notes
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Suppose that in a gravimetric analysis, you forget to dry the filter crucibles before collecting precipitate. After filtering the product, you dry the product and crucible thoroughly before weighing them. Is the apparent mass of the product always high or always low?
    

Is the error in the mass systematic or random? Select all that apply.

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6. –/8 points HarrisChem9 3.P.018. My Notes
Question Part
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–/8
 
(a) Show that the formula mass of NaBr is 102.894 (±0.001) g/mol. (Enter exact values for the atomic masses and uncertainties. Enter unrounded values for the calculated answers. Use at least two more digits than given.)
Na      = (No Response) seenKey

22.98976928

 ± (No Response) seenKey

0.00000002

 g/mol
Br      = (No Response) seenKey

79.904

 ± (No Response) seenKey

0.001

 g/mol
NaBr      = (No Response) seenKey

102.89377

 ± (No Response) seenKey

0.00100

 g/mol

(b) To prepare a solution of NaBr, you weigh out 2.611 (±0.003) g and dissolve it to specification in a volumetric flask whose volume is 100.00 (±0.08) mL. Express the molarity of the solution, along with its uncertainty, with an appropriate number of digits.
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0.2538

 ± WebAssign will check your answer for the correct number of significant figures.(No Response) seenKey

0.0004

 M

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7. –/2 points HarrisChem9 3.P.023. My Notes
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–/2
 
Avogadro's number can be computed from the following measured properties of pure crystalline silicon: (1) atomic mass (obtained from the mass and abundance of each isotope), (2) density of the crystal, (3) size of the unit cell (the smallest repeating unit in the crystal), and (4) number of atoms in the unit cell. For the material that was used, the average atomic mass of Si is
mSi = 28.0853842 (35) g/mol,
 where 35 is the uncertainty (standard deviation) in the last two digits. The density is
ρ = 2.3290319 (18) g/cm3,
 the size of the cubic unit cell is
co = 5.43102036 (33) ✕ 10−8 cm,
 and there are 8 atoms per unit cell. Avogadro's number is computed from the equation below.
NA = 
mSi
(ρco3)/8
From the measured properties and their uncertainties, compute Avogadro's number and its uncertainty. To find the uncertainty of co3, use the function
y = xa
 in the rules for propagation of uncertainty table.
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6.0221369e+23

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4.8e+17

 mol−1

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