TCHEM 162 Clark Atlanta Oxytocin Gaze Positive Loop Lab Report

TCHEM 162 Lab 4 AnalysisTYPE a post lab summary which includes the items in italicized bold-type below, filled in or
answered. For this lab, you may copy and paste the tables and questions into your lab summary.
You MUST submit your post lab as a typed Word Document or PDF.
DATA ANALYSIS (20 points)
1. Fill out the following table from your lab data (3 points):
Table 1. Measured cell potentials for the spontaneous reactions
Electrochemical
Anode
Cathode
Cell Pair
(oxidation) (reduction)
Measured Eocell (V)
Theoretical Eocell (V)
% error
Cu & Fe
Cu & Pb
Cu & Zn
Zn & Pb
Zn & Fe
Fe & Pb
2. Show your calculation for the Theoretical Eocell value for the copper and zinc cell using the
reduction potentials in your textbook (2 points). Also show your calculation for % error of
the measured Eocell for copper and zinc (1 point).
Type equation here.
TCHEM 162 Lab 4 Analysis
3. For the concentration cell in Part 3, show the calculations for the expected potential (2
points), give the experimentally determined concentration cell potential (1 points) and
calculate the % error (1 point).
Type equation here.
4. Write the cell line notation for your battery in Part 4 (1 point) and give the measured
voltage (1 point). Remember to put the “;” between the two cells in the cell line notation.
Type equation here.
TCHEM 162 Lab 4 Analysis
5. Imagine that you need to make a galvanic cell with a measured potential of 0.50 V using
one of the measured Eocells from your table in Part 2.
a. Using the Nernst equation, pick a cell and determine the ratio of concentrations of
the anode ion and the cathode ion to reach a voltage of exactly 0.50 V. If one of
your cells had a measured voltage of exactly 0.50 V, then answer this question for a
measured potential of 0.51 V (4 points).
Type equation here.
b. Using the ratio of concentrations that you found in 5a, explain how you would
dilute the anode or cathode to achieve this ratio. Assume that you can use a 1.000
mL automatic pipette, a 5.00 mL automatic pipette and as many beakers as you
want. You will need at least 2 mL of the diluted solution to fill up your half-cell.
Give specific numbers in your answer (4 points).
Type equation here.
Lab 4 Write Up: Abstracts
Background on Abstracts
An abstract is a summary of a scientific paper. Readers read the abstract to decide whether the
paper is relevant to them. The content of an abstract must be accessible enough that the reader
can understand it without needing a large amount of background information, but specific
enough that the reader will know whether they are interested in further reading.
Typically, an abstract includes the following.
• An explanation of why the topic is important in your field/s.
• Your specific research question/problem
• An indication of your research methods and approach.
• A summary of the key results.
• An explanation of why your findings and key message contribute to the field/s and
possible future research directions.
Below is a real abstract for a paper published in the Science, one of the most prestigious journals
in the world. 1 This paper is also a fun read if you ever have some free time.:
Title: Oxytocin-gaze positive loop and the coevolution of human-dog
bonds
Abstract:
Human-like modes of communication, including mutual gaze, in dogs
may have been acquired during domestication with humans. We show
that gazing behavior from dogs, but not wolves, increased urinary
oxytocin concentrations in owners, which consequently facilitated
owners’ affiliation and increased oxytocin concentration in dogs.
Further, nasally administered oxytocin increased gazing behavior in
dogs, which in turn increased urinary oxytocin concentrations in
owners. These findings support the existence of an interspecies
oxytocin-mediated positive loop facilitated and modulated by gazing,
which may have supported the coevolution of human-dog bonding by
engaging common modes of communicating social attachment.
1
Nagasawa, Miho, et al. “Oxytocin-gaze positive loop and the coevolution of human-dog bonds.” Science 348.6232
(2015): 333-336.
Page 1 of 3
Lab 4 Write Up Assignment (15 points):
For the Lab 4 Write Up, you will write an abstract from Part 3, the concentration cell. Assume
that your audience is students who will perform this lab next quarter. The students know about
entropy and equilibrium, but do NOT know about electrochemistry and electrochemical
potential. Your Lab 4 Write up will be graded using the following rubric. The final abstract
will be one paragraph which includes:
Reason for writing (connection to the bigger picture):
In this section, answer why concentration cells are important to understand:
•
•
Give at least one example of an important application of a concentration cell. You can
look at the electrochemical cell chapter in the textbook for examples (1 points).
Explain why there is a voltage in a concentration cell and how this voltage relates to
change in entropy and equilibrium (2 points).
Problem:
In this section go from the larger picture of concentration cells to the concentration cells you
measured in lab.
• What concentration cell did you measure in lab specifically?
o Say what metal you used and give the concentrations of the two half cells for
this experiment. (2 points)
Methodology:
In this section, BRIEFLY explain how you measured potentials of the concentration cell:
• Give a very brief explanation of how you created the half cells and how you measured
the potential. You do not need to include any numbers, just give a qualitative overview.
This part should be 1 – 2 sentences. (2 point)
Results:
• Give your specific the voltage you measured for the concentration cell (1 point).
• Give the theoretical voltage and the % error from the theoretical values (2 points).
Implications:
•
Explain what changes should be implemented from the findings of your work. What
recommendations would you have for future students performing this experiment to
lower the percent error? (3 points). This should be 1 – 2 sentences.
Your abstract must be less than 400 words (2 points) which is a typical limit for journals.
Page 2 of 3
Write your abstract below:
Page 3 of 3
ELECTROCHEMICAL CELL LAB
“ELECTROCHEM LAB”
INTRODUCTION
A redox reaction involves the transfer of electrons from one chemical species to another. In an
electrochemical cell, the oxidation process and the reduction process are separated into two halfcells connected by an external wire. The half-cell with the oxidation process is losing negative
charge (e- loss) while the half-cell with the reduction process is gaining negative charge (e- gain).
A salt bridge must connect the two half-cells to permit the transfer of ions between the two
solutions completing the electrical circuit.
The transfer of electrons through the external wire creates a current that can do work. The
driving force pushing the electrons through the wire is the difference in the attraction for
electrons in the two half-cells. This potential energy difference is called the cell potential
(Ecell) and is measured in volts. The standard cell potential (Eocell) is directly related to the
magnitude of the equilibrium constant for the overall oxidation-reduction reaction occurring in
the cell. A reaction that more strongly favors product formation (larger K) will have a larger
Eocell than a reaction which only moderately favors product formation.
By definition, oxidation takes place at the anode and reduction takes place at the cathode.
Electrons flow from the anode to the cathode occurs through a wire connecting the electrodes.
The anode is designated as the “negative” electrode since it has a relative excess of electrons (or
negative charge) and the cathode is designated as the “positive” electrode since it has
a relative deficiency of electrons.
Standard cell potentials (E°cell) can be calculated from electrode potentials (E°) measured
under standard conditions (1.00 M solutions, 1.00 atm pressure, 298 K) using the equation shown
below:
E°cell = E°cathode – E°anode
(1)
A positive cell potential is observed for reactions that proceed spontaneously in the direction the
reaction is written; a reaction with a negative cell potential proceeds spontaneously in the reverse
direction.
When the concentrations of solutes or partial pressures of gasses are not at standard conditions,
the cell potential (Ecell) can be determined by the Nernst equation (2):
𝑅𝑇
𝐸𝑐𝑒𝑙𝑙 = 𝐸°𝑐𝑒𝑙𝑙 − 𝑛𝐹 ln (𝑄) (2)
Where:
R = ideal gas constant, 8.3145 J/molK
T = temperature in Kelvin
n = moles of e− transferred
F = Faraday’s constant, 96,485 C/mol eQ = reaction quotient
At 298K, RT/F is 0.0257 V.
The Standard Potential Table in your textbook lists many electrode half-reactions and their
potentials. These potentials are measured relative to the Standard Hydrogen Electrode (SHE)
which has the half-reaction:
2H+(aq) + 2e–
H2(g)
E° = 0.00 V.
These reactions are listed as reductions. The species most easily reduced have large positive
potentials and the species most easily oxidized have large negative potentials.
Cell notation has been devised as a shorthand way of describing galvanic cells. The reaction at
the anode, cathode, reaction conditions (concentration, pressure, etc.) and the type of electrodes
are all described.
Cell notation rules are described below:
1. The anode half-reaction is written on the left and the cathode half-reaction on the right.
Within a given half-cell the reactants are specified first and products last. As the reader’s
eye proceeds from left to right, they are reading a description of the oxidation reaction
first and then the reduction reaction (in other words – the direction of electron flow).
Spectator ions are not included in the description.
2. A single vertical line indicates that species are in different phases but in physical contact
with each other. A double vertical line indicates a salt bridge or porous membrane
separating the individual half-cells.
3. The phase of the species is always shown in parentheses. If the substances in the cells are
not in their standard states then their concentration, pressure or temperature should be
indicated in brackets. Conversely, if no concentration, pressure or temperature is noted
the species in the cells are assumed to be at standard conditions (1.00 M or 1.00 atm and
298K).
For example, a galvanic cell is constructed from solutions in two beakers connected by a salt
bridge and an external wire. One beaker contains 0.15 M Cd(NO3)2 and a Cd metal electrode.
The other beaker contains 0.20 M AgNO3 and Ag metal electrode. The net ionic equation for
the cell reaction is:
2Ag+(aq, 0.20 M) + Cd(s)
Cd2+(aq, 0.15 M) + 2Ag(s)
In the reaction above Cd(s) is oxidized (the anode) to form Cd2+(aq) and Ag+(aq) is reduced (the
cathode) to form AgO(s).
Cd2+(aq, 0.15 M) + 2e–
Anode:
Cd(s)
Cathode:
Ag(aq, 0.20 M) + e–
Using the rules above the cell notation is:
Ag(s)
Cd(s) | Cd2+(aq)(0.15 M) || Ag+(aq) (0.20 M) | Ag(s)
A Concentration Cell is an electrochemical cell in which concentration differences between cell
compartments containing the same components provides the driving force behind difference in
cell potential.
For a cell comprised of half-cell containing 1.0 M Cu2+ and another half-cell containing 0.0100
M Cu2+ the half-cell reactions would be:
Anode:
Cu(s) →
Cathode:
Cu2+(aq) (1.0 M) + 2e- → Cu(s)
Cu2+(aq) (0.0100 M) + 2e-
Overall the system will move towards the half-cells having an equal intermediate concentration
of Cu2+. As the concentrations change the half-cell potentials would converge to a common value
once the concentrations are equal the reaction would cease, and the Ecell will equal zero.
The purpose of this experiment is to investigate electrode potentials for several electrochemical
half-cells and explore the effect of concentration on electrode potential.
In Part 4 of the lab, you will connect electrochemical cells to create a battery. You will need to
connect the cells in series, which is Anode –> Cathode–> Anode –> Cathode. When connected
like this, the measured cell potential will be the sum of the individual cell potentials.
The cell line notation for a battery is the cell line notation for each electrochemical cells with a
semicolon, “;” in between the electrochemical cells.
PRE-LAB ASSIGNMENT
Read through the lab manual. Review electrochemical cells and concentration cells in the
textbook.
LAB NOTEBOOK SET-UP
•
Title
Record the title of this lab, the date you are doing it, your name, and your partner’s name
on a fresh page of your lab notebook.
•
Lab Objective(s)
As you read the lab, try to figure out WHY you are doing it – what questions do you hope
your data will allow you to answer when you are done? After you have read all the way
through the post-lab questions, come back and write your objectives.
•
Hypothesis
1) Explain how you know you are measuring Eocell in Part 2 of this lab, even though
the concentrations of the ion solutions are 0.1 M in this lab, not 1 M. (Hint, think
about the reaction quotient, Q)
2) Predict the voltage for the copper concentration cell in Part 3. Explain how you
determined your answer. Assume the room temperature is 20.0 oC.
3) Describe the setup for your battery in Part 4 and predict the voltage of the battery.
Explain how you determined your answer.
•
Physical & Chemical Properties Table
Here is a sample table. Copy this table into your lab notebook and finish filling in the
shaded areas. INCLUDE ALL REACTANTS AND PRODUCTS.
Chemical
Name
•
Chemical
Formula
Physical and Chemical
Properties
Purpose/ Use in
THIS Lab
Hazards & Response to
Exposure & Spills
Pre-Lab Questions
Answer the following questions BEFORE LAB. Your answers should be written in your lab
notebook. You do not need to include the graph in your notebook.
1) Fill out the following table with the reduction half reactions and reduction potentials
from your textbook.
Metal/Ion Pair
Cu2+/Cu
Pb2+/Pb
Zn2+/Zn
Fe2+/Fe
Reduction half-reaction
(include states of matter)
Standard Reduction
Potential, Eo (V)
2) Fill out the following table. Use the standard reduction potentials from your textbook to
calculate the theoretical standard electrochemical cell potential, Eocell. Do not use sources
other than your textbook.
Electrode Pair
Balanced, spontaneous, NET IONIC equation
(include states of matter)
Theoretical Eocell
(V)
Cu & Fe
Cu & Pb
Cu & Zn
Zn & Pb
Zn & Fe
Fe & Pb
3) Explain why you will measure the standard cell potential, Eocell, in Part 2 of this lab, even
though the metal ion concentrations are 0.1 M NOT 1 M.
•
Reaction Equations
Your balanced reactions should be in Pre-Lab Question #2.
•
Material & Methods
Remember you will NOT be allowed to bring this lab manual to the lab. Write instructions
for the experimental procedure from the procedure given below. You may want to draw
pictures or diagrams or a flow chart. A reference copy of the lab will be available from the
instructor if you and your partner are confused about any details. The section which follows
the Materials & Methods one contains the tables and data spaces you need to copy into your
lab notebook for recording data.
MATERIALS, METHODS, AND LAB PROCEDURES
Materials:
Materials and Chemicals
•
•
•
•
•
•
•
0.1 M Cu(NO3)2 solution
0.1 M FeSO4 solution
0.1 M Zn(NO3)2 solution
0.1 M Pb(NO3)2 solution
0.1 M KNO3 solution
1.0 x 10-4 M Cu(NO3)2 solution
Cu, Fe, Pb, Zn electrodes
Equipment
•
•
•
•
•
•
•
•
•
•
Sandpaper
Cellulose film
6 small pieces of PVC piping
Electrical leads
3 alligator clips
Fluke Multimeter
Current probe
Small beaker
2 x 150 mL beaker
Waste beaker
Using the Fluke Multimeter
Watch the following video on how to use a Fluke multimeter and write a methods section in your
lab notebook. Video link: https://www.youtube.com/watch?v=JQH7ydkBgcE
NOTE: Your electrochemical cell set-up will look different from the electrochemical cell in the
video.
Part 1. Assembling half cells
1) Wet a piece of cellulose film (taken from the spool) in water.
2) Cut the cellulose paper squares so that they are only slightly larger than the acrylic tubes.
3) Carefully place a square piece of cellulose film over the smoother end of the acrylic tube
and secure the cellulose on the end of the tube by sliding the PVC band over the filmcovered tube end, being careful not to rip the film (the PVC will be clear, not brown like
in Figure 1).
4) Make sure the film is stretched tightly and is wrinkle-free, to prevent leaks and provide a
reliable porous membrane for the “salt bridge.”
5) Use DI water to test for leaks prior to adding any metal ion solution in the final assembly
steps.
6) Rinse the inside of the tube with the desired metal ion solution into the waste then place a
metal ion solution. DO NOT FILL THE TUBE TO THE TOP. You only need enough
solution to submerge the metal electrode, roughly half way up the tube.
Figure 1.Constructing a half cell.
7) Sand the bottom of the metal electrodes and place the corresponding metal electrode into
the half-cell such that the metal is in contact with the solution, but is NOT touching the
cellulose film. For example, you will place the copper electrode in the half-cell with the
0.1 M Cu(NO3)2 solution.
Figure 2. Diagram of the 0.10 M copper half-cell
8) Repeat this procedure for 0.1 M FeSO4 and a Fe electrode, 0.1 M Pb(NO3)2 and a Pb
electrode and 0.1 M Zn(NO3)2 and a Zn electrode.
9) Record the solution concentrations on the bottle in Data Table 1.
10) Make one other half cell and set it aside. You will fill this cell in Part 3.
Part 2: Measuring Standard Cell Potentials
11) Place the assembled half-cells into a 150 mL beaker and add the KNO3 solution to the
bottom of the beaker so that the bottoms of the electrodes are immersed in the KNO3
solution. You may want to make 2 beakers if all the half-cells do not fit into one beaker.
The half cells must be in the same beaker to measure the potential.
Figure 3. Diagram of a completed electrochemical cell composed of two half cells in a
KNO3 salt bridge solution.
12) Measure the potentials for each electrochemical cell in Data Table 2. The measured
voltages must be positive. Indicate in Data Table 2 which metal in the anode and which
is the cathode.
13) Using the theoretical cell potential from your Pre-Lab Question 2, calculate the percent
error for your cell potential measurements. Show your calculations for the Cu & Fe pair.
Part 3: Copper Concentration Cell
14) With the remaining tube, prepare a half cell with the 1.0 x 10-4 M Cu(NO3)2solution and a
Cu electrode following the instructions in part 1.
15) Construct an electrochemical cell as in Part 2 using this half-cell and the half-cell
containing the 0.1 M Cu(NO3)2 solution. Measure and record the positive cell potential.
Figure 4. Diagram of the copper concentration cell in this lab.
16) Use the Nernst equation (2) to calculate the theoretical cell potential in the data section of
your lab notebook.
17) Calculate the % error of your measured cell potential to the theoretical cell potential in
the concentration cell.
Part 4: Making a Battery
18) Connect your half cells together such that the measured potential is greater than the
highest measured cell potential in Data Table 2. You will need to connect the cells in
series, which is Anode –> Cathode–> Anode –> Cathode (Hint: you will need to use an
additional alligator clip). Make sure that each Anode/Cathode pair is in the same beaker.
19) Write down the voltage in the data section of your lab notebook.
20) Write the cell line notation for the battery in the data section of your lab notebook. When
going from the cathode to the anode, use a semicolon in your cell line notation.
21) Calculate the theoretical voltage of your battery using the standard reduction potentials in
Data Table 2 and calculate your % error.
DATA SECTION:
Part 1. Measuring Cell Potentials
Data Table 1. Half-cell solution concentrations
Solution
Concentration on the Bottle (M)
0.1 M Cu(NO3)2 solution
0.1 M FeSO4 solution
0.1 M Zn(NO3)2
0.1 M Pb(NO3)2
1.0 x 10-4 M Cu(NO3)2
Record any observations from making your half cells.
Part 2. Measuring Standard Cell Potentials
Data Table 2. Measured cell potentials for the SPONTANEOUS reactions
Electrochemical
Anode
Cathode
Cell Pair
(oxidation) (reduction)
Cu & Fe
Cu & Pb
Cu & Zn
Zn & Pb
Zn & Fe
Fe & Pb
Measured Eocell (V)
Theoretical Eocell (V)
(from Pre-Lab question 2)
% error
Calculations for % error of Cu & Fe electrochemical cell:
% 𝒆𝒓𝒓𝒐𝒓 =
|𝒎𝒆𝒂𝒔𝒖𝒓𝒆𝒅 − 𝒕𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍|
𝒙 𝟏𝟎𝟎%
𝒕𝒉𝒆𝒐𝒓𝒆𝒕𝒊𝒄𝒂𝒍
Observations that could affect your results:
Part 3: Copper Concentration Cell
Temperature of the room: ______________
Measured cell potential of concentration cell:
Nernst equation:
R = 8.3145 J/molK
_____
𝑹𝑻
𝑬𝒄𝒆𝒍𝒍 = 𝑬°𝒄𝒆𝒍𝒍 − 𝒏𝑭 𝐥𝐧(𝑸)
F = 96,485 C/mol e-
Calculation for theoretical cell potential, Ecell (remember than temperature must be in Kelvin):
Theoretical cell potential of concentration cell:
Calculations for % error of concentration cell:
% error: ________________
Cell line notation for the concentration cell:
______
Part 4: Making a Battery
Measured voltage of the battery: _______________
Cell line notation for the battery (separate the 2 electrochemical cells in with a semicolon, 😉
Calculation of the theoretical battery voltage:
Theoretical battery voltage: _________________
% error of the battery voltage: ____________________