. Does the value of the equilibrium constant change when the concentration of either the reactants or products is altered? Why or why not? Explain this based on your calculations of Keq:
. Does the value of the equilibrium constant change when the concentration of either the reactants or products is altered? Why or why not? Explain this based on your calculations of Keq:
Chemistry by OpenStax (2015-05-04)
1st Edition
ISBN:9781938168390
Author:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Publisher:Klaus Theopold, Richard H Langley, Paul Flowers, William R. Robinson, Mark Blaser
Chapter15: Equilibria Of Other Reaction Classes
Section: Chapter Questions
Problem 11E: The Handbook of Chemistry and Physics (http://openstaxcollege.org/l/16Handbook) gives solubilities...
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help with Part B Please.
5. Compare the values of Keq for each of the five solutions:
a. Are any of the values outside the sample standard deviation for the set?
b. Does the value of the equilibrium constant change when the concentration of either the reactants or products is altered? Why or why not? Explain this based on your calculations of Keq:
c. What caused variation (three reasons) in your values of Keq?
- NOTE: the standard deviation is 3.9x102
- The procedure is in the images
Data:
| Unknown solution | Equilibrium concentration of {FeNCS2+} in unknown solution(M) | Equilibrium concentration [Fe3+](M) | Equilibrium concentration [SCN-](M) | Keq |
| 1 | 3.7x10-5 | 9.6x10-4 | 1.6x10-4 | 2.4x102 |
| 2 | 6.2x10-5 | 9.4x10-4 | 3.4x10-4 | 1.9x102 |
| 3 | 1.1x10-4 | 8.9x10-4 | 4.9x10-4 | 2.5x102 |
| 4 | 1.1x10-4 | 8.9x10-4 | 6.9x10-4 | 1.8x102 |
| 5 | 1.8x10-4 | 8.2x10-4 | 8.2x10-4 | 2.7x102 |
Transcribed Image Text:2. Make a data table that allows you to record the actual volumes of the solutions you use to make
the unknown solutions. Record what you actually do-do not assume that just be- cause the
lab manual says to add a particular volume, that you actually added that volume. Always record
what
you
do!
Colorimetric Method to Determine the Equilibrium Concentration of
{FENCS}2+
Use test tubes (18 x 150 mm) that have approximately the same diameter. Prepare a table in your
notebook to collect data containing the following information for each of the five unknown
solutions.
• Unknown solution #
Matching standard concentration (of {FeNCS}2+) and/or identity (A-D)
Depth of standard solution
Depth of unknown solution
Colorimetric Procedure
1. Transfer unkown mixture #1 to a clean test tube, saving the beaker (labeled 1) for use in step
3. Using a sheet of white paper on the laboratory bench as a background, hold the test tube
containing Solution #1 next to test tube A. Look directly down both these test tubes to compare
color intensities. Replace test tube A with each of the other standards B-D, comparing color
intensities each time, until you find one that matches closely with the unknown solution
#1. You may find that the color intensity of solution #1 lies between that of two successive
standards, thus establishing a concentration range for equilibrium solution #1. The method
used here is the standard series method.
2. If unknown solution #1 closely matches one standard solution (which should be less intense
than solution #1), proceed to step 3. If solution #1 has a color intensity between two successive
standards, select the standard of lower concentration to continue with Step 3.
3. Now, you will use the balancing method to determine accurately the equilibrium concentration
of {FENCS2+}. Using the standard selected in Step 2, place it side by side with unknown solution
#1 against a white background. If you have selected the correct standard, you will find that
its color is slightly less intense than that of the unknown solution. Carefully pour out small
volumes of the unknown solution into the beaker labeled 1, until the color intensities of the
unknown solution and standard are matched very closely. Measure the depths of the matching
columns of standard and unknown solutions, using a ruler, and record your data in the
appropriate space in your lab notebook. Return the unknown solution from the test tube to the
appropriate beaker.
4. If you have only one test tube, wash the test tube from step 3 well, rinse with distilled water,
and finally rinse with a small amount of unknown solution #2. Fill the test tube with the
remaining unknown solution #2. Repeat steps 1-3 to match color intensities using first the
standard series method and then the balancing method. Record your measured depths of the
matching columns.
5. Perform step 4 for each of the remaining unknown solutions #3, #4, and #5.
![M
with the letters A-D. Label your volumetric flask with the letter corresponding to the standard
Stock Solutions (I-IV)
comm
option
tube, and pass the remaining solution to the other members of your group. Obtain about 20 mL
Each student in each group will obtain all four of the following from the reagent bench to prepare
Standard and Equilibrium Solutions. The solvent for all solutions is 0.5 M nitric acid, which prevents
the precipitation of the Fe as Fe (OH),.
Standard solution
[Fe"],"
(SCN ].
7.5mL
5mL
2.5mL
1.0mL
1.5 x 10 M
II
III
IV
1.0 x 10 M
- 60 mL of Fe(N0,),
70 mL of Fe(NO,),
2 x 10 M in 0.50 M HNO,
0.20 M in 0.50 M
40 mL KSCN
C
5.0 x 10 M
HNO,
2 x 103 M in 0.50 M HNO,
100 mL HNO,
Used to make Equilibrium
0.50 M
2.0 x 10 M
Used to make
Used to make both
Solutions
Standard and Equilibrium
Standard Solutions
Used as solvent for
*Determined as part of the pre-lab exercise.
Solutions
all solutions
2. Although your TA will check your calculations, each group is responsible for the proper
Preparation of its own set of solutions. The members of the group should decide who will
prepare each solution. They should check each other's calculations and proposed procedure
to make sure that each of the solutions will be properly prepared. Each student in the group
These stock solutions will be available in containers or carboys. Obtain only the quantities specified
above in clearly labeled glassware (beakers or Erlenmeyer flasks). Please do not take any more of
these solutions than called for in this experiment! Wastes must be kept to a minimum. Label your
beakers/flasks carefully and note the actual concentrations as recorded on the containers.
soluticr sign up for one 100.00 mL volumetric flask and prepare only one of the standard
solutions A-D. Each student will obtain about 20 mL of each of the other four standard
solutions from members of the group. To avoid confusion, label four clean, dry test tubes
Preparation of Standard Solutions (A-D)
solution that you prepared. Save about 20 mL of your standard solution in the appropriate test
of each of the other four standard solutions, taking special care to put them in the appropriate
test tubes. You must have a complete set of about 20 mL of each of the standard solutions, A-D,
in your labeled test tubes.
NOTE: As discussed above, each of these standard solutions will contain a rather high concentration
of Fe3+, which reacts with various much lower concentrations of SCN. This means that the
equilibrium Fe+ + SCN = {FeNCS}²+ will be forced far to the right, causing essentially all of the
SCN to be converted to the {FeNCS}2+ complex ion [Why?]. The [SCN ], is known, and you can
assume that all of it reacts to form {FeNCS}2+ therefore the concentration of {FeNCS}2* present can
be calculated. (They are not exactly equal because of the dilution of the solution through the mixing
of solutions.)
in
3. Be sure to record what you did to make your solution and the names of the other people your
group. Make a table with the concentrations of the solutions in your standard series.
Unknown Mixtures. (Work in pairs from this point on)
1. Prepare five unknown mixtures (1-5) by adding the amounts indicated to separate,labeled, ary
beakers. Mix thoroughly.
1. Four standard solutions (100.00 mL each) with varying initial concentrations of KSCN will
be prepared. You will work in groups of four to prepare these standard solutions-each one
of you preparing 100 mL of one standard. By sharing 20 mL of each of the solutions
the members of each group, each of you will end up with the complete set of standard solu-
mL of IV
Solution #
mL of II
mL of III
among
8.0
1
10.0
2.0
tions, A-D.
6.0
10.0
4.0
Each standard solution is prepared in a 100 mL volumetric flask by placing into the flask:
3
10.0
6.0
4.0
a. 50.0 mL of Solution I (measured with a graduated cylinder). This will give you excess Fe*
2.0
4.
10.0
8.0
in the final solution.
b. the calculated volume* of Solution III, measured with a graduated pipette, that gives the
desired initial concentration of KSCN when the final volume of 100.00 mL is reached.
10.0
10.0
0.0
c. enough of Solution IV to bring the total volume up to the 100 mL line on the
volumetric flask.
NOTE: You will need to use a graduated pipette to deliver solutions III and IV. It is more
important to know the volume added as accurately as possible rather than to add exactly 2, 4, 6
or 8 mL. (Your TA will explain how to do this.)
5mL
The initial concentrations of Fet and SCN in the standard solutions are:
1.0X10TM xDomL](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F688553c1-a29d-4d73-a765-adb59e2cd2b6%2F3b29da91-9609-4a28-872c-950f1864cb77%2Fclonfuo_processed.jpeg&w=3840&q=75)
Transcribed Image Text:M
with the letters A-D. Label your volumetric flask with the letter corresponding to the standard
Stock Solutions (I-IV)
comm
option
tube, and pass the remaining solution to the other members of your group. Obtain about 20 mL
Each student in each group will obtain all four of the following from the reagent bench to prepare
Standard and Equilibrium Solutions. The solvent for all solutions is 0.5 M nitric acid, which prevents
the precipitation of the Fe as Fe (OH),.
Standard solution
[Fe"],"
(SCN ].
7.5mL
5mL
2.5mL
1.0mL
1.5 x 10 M
II
III
IV
1.0 x 10 M
- 60 mL of Fe(N0,),
70 mL of Fe(NO,),
2 x 10 M in 0.50 M HNO,
0.20 M in 0.50 M
40 mL KSCN
C
5.0 x 10 M
HNO,
2 x 103 M in 0.50 M HNO,
100 mL HNO,
Used to make Equilibrium
0.50 M
2.0 x 10 M
Used to make
Used to make both
Solutions
Standard and Equilibrium
Standard Solutions
Used as solvent for
*Determined as part of the pre-lab exercise.
Solutions
all solutions
2. Although your TA will check your calculations, each group is responsible for the proper
Preparation of its own set of solutions. The members of the group should decide who will
prepare each solution. They should check each other's calculations and proposed procedure
to make sure that each of the solutions will be properly prepared. Each student in the group
These stock solutions will be available in containers or carboys. Obtain only the quantities specified
above in clearly labeled glassware (beakers or Erlenmeyer flasks). Please do not take any more of
these solutions than called for in this experiment! Wastes must be kept to a minimum. Label your
beakers/flasks carefully and note the actual concentrations as recorded on the containers.
soluticr sign up for one 100.00 mL volumetric flask and prepare only one of the standard
solutions A-D. Each student will obtain about 20 mL of each of the other four standard
solutions from members of the group. To avoid confusion, label four clean, dry test tubes
Preparation of Standard Solutions (A-D)
solution that you prepared. Save about 20 mL of your standard solution in the appropriate test
of each of the other four standard solutions, taking special care to put them in the appropriate
test tubes. You must have a complete set of about 20 mL of each of the standard solutions, A-D,
in your labeled test tubes.
NOTE: As discussed above, each of these standard solutions will contain a rather high concentration
of Fe3+, which reacts with various much lower concentrations of SCN. This means that the
equilibrium Fe+ + SCN = {FeNCS}²+ will be forced far to the right, causing essentially all of the
SCN to be converted to the {FeNCS}2+ complex ion [Why?]. The [SCN ], is known, and you can
assume that all of it reacts to form {FeNCS}2+ therefore the concentration of {FeNCS}2* present can
be calculated. (They are not exactly equal because of the dilution of the solution through the mixing
of solutions.)
in
3. Be sure to record what you did to make your solution and the names of the other people your
group. Make a table with the concentrations of the solutions in your standard series.
Unknown Mixtures. (Work in pairs from this point on)
1. Prepare five unknown mixtures (1-5) by adding the amounts indicated to separate,labeled, ary
beakers. Mix thoroughly.
1. Four standard solutions (100.00 mL each) with varying initial concentrations of KSCN will
be prepared. You will work in groups of four to prepare these standard solutions-each one
of you preparing 100 mL of one standard. By sharing 20 mL of each of the solutions
the members of each group, each of you will end up with the complete set of standard solu-
mL of IV
Solution #
mL of II
mL of III
among
8.0
1
10.0
2.0
tions, A-D.
6.0
10.0
4.0
Each standard solution is prepared in a 100 mL volumetric flask by placing into the flask:
3
10.0
6.0
4.0
a. 50.0 mL of Solution I (measured with a graduated cylinder). This will give you excess Fe*
2.0
4.
10.0
8.0
in the final solution.
b. the calculated volume* of Solution III, measured with a graduated pipette, that gives the
desired initial concentration of KSCN when the final volume of 100.00 mL is reached.
10.0
10.0
0.0
c. enough of Solution IV to bring the total volume up to the 100 mL line on the
volumetric flask.
NOTE: You will need to use a graduated pipette to deliver solutions III and IV. It is more
important to know the volume added as accurately as possible rather than to add exactly 2, 4, 6
or 8 mL. (Your TA will explain how to do this.)
5mL
The initial concentrations of Fet and SCN in the standard solutions are:
1.0X10TM xDomL
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