QUIM4015_informelab_CyclicVoltammetry_AngelizGiovanni
docx
keyboard_arrow_up
School
UPR Mayagüez *
*We aren’t endorsed by this school
Course
4015L
Subject
Chemistry
Date
Feb 20, 2024
Type
docx
Pages
15
Uploaded by ElderRock13387
2013
Graphite Furnace Atomic Absorption Spectroscopy Chromium
September 13, 2013
Determination of Ascorbic
Acid in Drinks and Nutritional
Supplements with Cyclic Voltammetry
Angeliz Caro Monroig
Giovanni Gonzalez Albo
Intructor: Queziel Rivera
Analytical Chemistry Division
QUIM3065 Sec060L
#5
GF-AAS
2
Abstract: Cyclic voltammetry is considered a very useful because it provides valuable
information about an electrochemical system, like for example, the chemical
reversibility of a redox reaction. This technique was used to measure the
concentration of Ascorbic Acid in a supplement tablet and compare it to the
reported value. A large amount of the population doesn’t consume the
recommended daily intake of 75 mg for women and 90 mg of Vitamin C for men
so they depend in taking this supplement to meet the body necessity for Ascorbic
Acid. This determination helped validate if the Members Mark
TM
Vitamin C
500mg supplement would provide the consumer with the alleged amount. For the
Vitamin C supplement, it was found that the tablet contained 452.72
±0.03
mg of
ascorbic acid. The value stated on the product label was 500mg. This is equal to a
% difference of 9.46% between the theoretical and experimental values. The
percent per weight of ascorbic acid in the supplement was also determined,
resulting in a value of 70.88%. Since there aren’t strict regulations with
Introduction:
Cyclic voltammetry is considered the most informative electrochemical
technique. This technique is very useful because it provides very valuable
information about an electrochemical system like for example the chemical
reversibility of a redox reaction. In cyclic voltammetry the voltage is in excess of
that predicted by the Nernst equation and the current that develops in the
electrochemical cell is measure. The reversibility of a redox reaction can be seen
by this method because after the CV reaches a certain potential, the working
electrode potential ramp is inverted.
The CV has three electrodes that have different functions in a
electrochemical cell. The first is the working electrode made of glassy carbon and
is where the reaction takes place, the function of this electrode is to control the
potential. The reference electrode is made of silver in silver chloride solution and it
is use as a reference standard for the working electrode, it functions as a 0 for the
working electrode. The auxiliary electrode is made of platinum and it is needed for
current flow. The electrons in solution are attracted by the working electrode, this
electrons saturates the electrode. To prevent the saturation of the working electrode
the auxiliary electrode sends pulsations to “organize the electrons”.
GF-AAS
3
There are three types of redox reactions: the reversible, quasi-reversible and
the irreversible. The reversible redox reaction is seen when the cyclic
voltammogram is symmetrical which means that the redox species in the solution
can donate or accept electron without any problem, it is easy for the redox species
to be oxidized and then reduce or vice versa to return to its initial state. Another
type of redox reaction is the quasi-reversible which is a redox reaction which can
donate or accept an electron but when the voltage is reverse it is difficult for the
specie to return to its original state by accepting or donating an electron, it is not as
favorable. The last redox reaction is an irreversible one which is when the redox
reaction only goes one way after it donates or accepts it cannot come back to the
original state; the cyclic voltammogram of this reaction is completely
asymmetrical.
This technique was used to measure the concentration of Ascorbic Acid in a
supplement tablet, this method can be used because vitamin C is a molecule that
can undergo redox reaction and any method that employs redox reaction can be
study with cyclic voltammetry. Another way to find the concentration of this acid
is by the titration of ascorbic acid with iodine. Many people don’t eat enough fruits in a day to consume the recommended
daily intake of 75 mg for women and 90 mg of Vitamin C for men (2) so they
depend in taking this supplement to meet the body necessity for Ascorbic Acid.
Vitamin C is essential in the human body for its role as an antioxidant and a free
radical scavenger, it is important for the body to convert the free radicals to more
stable molecules because these free radicals can cause cancer, heart disease and
arthritis (3). Vitamin C is also very important because it helps in the process of
producing collagen. Vitamin C is a water soluble vitamin which means that the
body doesn’t store it, the excess consume will not do any harm because it will be
expel from the body very fast but in the other hand since the body doesn’t retain
this vitamin the human body has to constantly be consuming Ascorbic acid to
supply the demand. It is very important for the people that consume this
supplement to be certain that the concentration of Ascorbic Acid in the tablet is in
the range that is indicated by the manufacturer. It is also important for the
manufacturer to know that their product is in the range of concentration of what
they are offering and this can be achieve with Cyclic Voltammetry.
Experimental
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
GF-AAS
4
Equipment
To obtain the CV (cyclic voltammograms) an Epsilon E was used with an
arrangement of three electrodes: the working electrode which had a surface made
of glassy carbon, a platinum auxiliary electrode and the reference electrode which
was a saturated calomel electrode of silver surrounded with a solution of silver
chloride.
Reagents
To make the buffers solid Citric acid was use with a formula weight of 192.13
g/mol provided by Fisher Scientific Company and Sodium Phosphate Dibasic with
a formula weight of 141.96 g/mol provided by Sargent-Welch. To produce an ionic
strength of .5M in the buffer Potassium Chloride with a formula weight of 74.55
g/mol was use, this reagent was provided by the instructor of the laboratory. A
tablet of vitamin C of the brand Members Mark- 500mg was use as the unknown. Experimental Procedure:
Preparation of the buffers
To prepare all the solutions that were needed for this experiment it was necessary
to prepared 1 L of pH 6 buffer with ionic strength of .5M, this was done by adding
45.2 g of Na2HPO4, 7.74g of H3C6H5O7 and 11.6 g of KCl to a 1L volumetric
flask and completing to the mark with distilled water. It was also necessary to
prepare 1 L of pH 2.2 buffer with ionic strength of .5M; this was done by adding to
a 1L volumetric flask 1.43 g of Na2HPO4, 20.6g of H3C6H5O7, 37.2 g of KCl
and completing to the mark with distilled water.
Preparation of the analytical standards
To prepare the standards that were going to be use for the calibration curve, a stock
solution had to be made with a concentration of .01M of Ascorbic Acid (AAc) in a
100 mL volumetric flask. From this stock solution three AAc standard with
concentration of 2.0x10^3M were made, this standard were made one with DI-
water, the other with pH 2.2 buffer and the last with pH 6 buffer in 50 mL
volumetric flasks. From the stock solution 4 additional 100 mL AAc std. were
prepared within 5x10
-4
to 6x10
-3
M range in buffer pH 2.2. Quality control
GF-AAS
5
One Qc standard of AAc was prepared in a 100 mL volumetric flask, within 5x10
-4
to 6x10
-3
M range in buffer pH 2.2.
Preparation of the commercial APAP sample (unk)
Before the solution of the AAc tablet was made the capsule had to be weight,
macerated and dissolved in pH 2.2 buffers. After the macerated tablet had been
dissolve this solution had to be quantitatively transferred to a 100 mL volumetric
flask and complete to the mark with pH 2.2 buffers. Then a 10 mL aliquot from the
previous made solution was transferred to a 100 mL volumetric flask and complete
to the mark with pH 2.2 buffer. This solution was called Unk. tablet aliquot.
Analysis of the solutions with a Cyclic Voltammogram (CV)
In this experiment a CV with three electrodes was use: a glassy carbon working
electrode, a platinum auxiliary electrode and silver in silver chloride reference
electrode. It is important to avoid tilting or drying the reference electrode. After
each run the auxiliary and reference electrodes have to be rinse with distilled water
and the working electrode has to be scraped in a surface which has alumina with
water.
The potential scan parameters were set as follow
Initial Potential
-0.1V
Sweep segments
2
High potential
+1.0
Sample interval
.001V
Low Potential
-0.1
Quiet time
10s
Direction of scan
Positive
Sensitivity
1x10
-4
A/V
Scan rate
50Mv/s
After the parameters are set the electrodes have to be clean and connected to
start the scans with standard of AAc in water. The scans were repeated three times,
the potential and the current were collected from each scan. Before removing the
solution from the CV the electrodes have to be disconnected and cleaned as was
explain earlier. The CV for the other two standard of AAc in buffer pH 2.2 and 6,
the four standards in pH 2.2 buffer, Qc and unknown aliquot were obtained in
GF-AAS
6
triplicate. After all the data was collected an analytical calibration was plotted for
the pH 2.2 standard to determine the AAc concentration in each of the original
samples.
Data Analysis
After obtaining all the cyclic voltammograms of the solution they were
compared with the figure 1 bellow.
Since the pH was manipulated in the samples it was seen how it affected the
analysis. After the calibration curve was made the R
2
, the equation of the line, and
limit of detection (LOD) was calculated. With the calibration curve the amount of
AAc in the tablet was determine with its propagated uncertainty, confidence level,
and percent of relative error. Based in the results from the Qc the reliability of the
experiment was determined. Safety Considerations
In this experiment is very important to use safety glasses to prevent eye irritation
due to many of the reactives that are being use. It is very important also to use
safety globes because many of the reactives are in a powder solid form. It is
important to use laboratory coat at all times to prevent the damaging of the clothes.
Results and Discussion:
Using the individual cyclic voltammograms, an overlay was created of all of
the cyclic voltammograms (
Figure 1.a)
. It was observed that the experimental
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
GF-AAS
7
voltammogram is inverted in comparison to the voltammogram presented in the
laboratory manual for the oxidation of Ascorbic Acid (
Figure 1.b)
. It is also
observed that the resulting currents are negative in the y-axis and results in a peak
current at 0.450V. This was surprising because Ascorbic Acid is a reducing agent
and therefore favors its oxidation. A literature search was conducted which
resulted in finding voltammograms that resemble the oxidation voltammogram
presented. The parameters used in the literature were compared to those found in
the laboratory manual and they were found to be very similar. Even though the
analytical parameters of the cyclic voltammogram were not changed by the
students prior to the analyzed, the parameters described in the literature and in the
manual were compared to those found in the data extracted from the cyclic
voltammogram. The difference between these parameters was found to be that the
voltage applied was negative. It was deduced that since this was the only different
factor in the analysis, the observed behavior must be attributed to it.
Because the voltage applied is negative, this means by definition that it is
heading towards the negative terminal. This is to say that we are adding electrons
to the sample; the sample was reduced. The initial potential was -100mV, the
switching potential was 1000mV and the final potential returned to -100mV. This
is why the voltammogram is inverted with respect to the oxidation voltammogram.
It is possible to observe how the current value increases as the voltage reaches
what should be the reduction potential of Ascorbic acid at pH=2.2 at these applied
potentials. The current then decreases as the ascorbic acid concentration near the
electrode surface diminishes. Another important observation is that the reaction is
not reversible because as the potential returns to the initial -100mV, the product
should be reoxidized demonstrating an oxidation peak with a shape that is similar
to the previously described reduction peak. Figure 1: Cyclic Voltammograms for different ascorbic acid concentrations
GF-AAS
8
a) experimental reduction
b) theoretical oxidation
In this analysis, the pH was varied to observe how it would affect the scan. As it is
observed, the current did not vary with change in solvent pH. However, the
potential did vary confirming the obvious assumption that redox potential is pH
dependent. Std Aac
Average Voltage
s
%RSD
Average Current
s %RSD
ddH2O
473.70
33.3
3
7.04
-31.460
3.01
8
-9.592
pH=2.2
638.40
6.60
1.03
-30.650
2.99
2
-9.763
pH=6.0
201.13
4.52
2.25
-29.257
4.01
7
-
13.730
Using the data obtained from the ascorbic acid standards, a calibration curve
was constructed and used to determine the concentration of Vitamin C in the
commercial tablet unknown sample. The equation for the calibration curved was
y=-19140x + 1.9217. The standard deviations for the slope and y-intercept were
797.923 and 1.9814, respectively. The LOD and LOQ for the calibration curve
analysis were also determined. The LOD was 0.000304 and the LOQ was
0.001012.
GF-AAS
9
0.00E+00
5.00E-04
1.00E-03
1.50E-03
2.00E-03
2.50E-03
3.00E-03
3.50E-03
4.00E-03
4.50E-03
-80.00
-70.00
-60.00
-50.00
-40.00
-30.00
-20.00
-10.00
0.00
f(x) = − 19139.79 x + 1.92
R² = 1
Standard Curve for Acetic Acid for the Analysis of a Vitamin C tablet unknown
Concentration
Current
Using this information, the amount of ascorbic acid in the commercial vitamin C
tablet was determined to be 454.72mg. The alleged value in the commercial tablet
is 500mg, allowing for a percent difference of 9.46%. For the analyzed tablet, it
was determined what the weight percentage of ascorbic acid was 70.88%. Table 1: Experimental and theoretical values of ascorbic acid mass in commercial Vitamin C tablet. tablet (g)
0.63870
aliquot (M)
0.00257
stock (M)
0.02570
grams
0.45272
experimental
(mg)
452.72
±0.04
theoretical (mg)
500.00
% difference
9.45
% w/w
70% ± .006
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
GF-AAS
10
Conclusion:
In this analysis, the reduction of Ascorbic Acid was observed experimentally
via Cyclic Voltammetry which resulted in a voltammogram with a negative current
peak with an unsymmetrical form showing the irreversible process. This technique
was used to determine the amount of ascorbic acid in a commercial vitamin C
tablet supplement was determined via cyclic voltammetry. Ascorbic Acid
standards were prepared and a calibration curve was constructed to find the
unknown concentration. The LOD and LOQ values were determined to ensure that
the analyte of interest was above the appropriate limits of detection and
quantification. For the Vitamin C supplement, it was found that the tablet
contained 452.72mg of ascorbic acid. A propagation error was done for this value,
resulting in ±0.03
. The value stated on the product label was 500mg. This is equal
to a % difference of 9.46% between the theoretical and experimental values. The
percent per weight of ascorbic acid in the supplement was also determined,
resulting in a value of 70.88%.
Supporting Information: Table 1: Experimental Data for Voltage for Cyclic Voltammetry
Solvent/
(M)
Potential
Averag
e
S
%RSD
Std Aac ddH2O
510.3
465.7
445.1
473.70
33.3
3
7.04
Std Aac pH=2.2
646
634.1
635.1
638.40
6.60
1.03
Std Aac pH=6.0
206.2
197.5
199.7
201.13
4.52
2.25
Std1
5.00E-04
441.4
437.5
427.7
435.53
7.06
1.62
Std 2
1.50E-03
454.9
448.9
448.4
450.73
3.62
0.80
Std 3
2.00E-04
418
415.8
413.6
415.80
2.20
0.53
Std 4
4.00E-03
449.5
436.4
437.5
441.13
7.27
1.65
Unknown
Vitamin C
Tablet 487.5
509.2
512.4
503.03
13.5
5
2.69
GF-AAS
11
Table 2: Experimental Data for Current for Cyclic Voltammetry
Solvent/(M)
Current
Average
S
%RSD
Std Aac ddH2O
-32.7
-33.66
-28.02
-31.460
3.018
-9.592
Std Aac pH=2.2
-33.57
-30.79
-27.59
-30.650
2.992
-9.763
Std Aac pH=6.0
-33.2
-29.4
-25.17
-29.257
4.017
-
13.730
Std1
5.00E-04
-7.34
-6.62
-8.89
-7.617
1.160
-
15.230
Std 2
1.50E-03
-25.43
-24.73
-23.13
-24.430
1.179
-4.826
Std 3
2.00E-04
-4.14
-3.45
-2.87
-3.487
0.636
-
18.235
Std 4
4.00E-03
-89.97
-65.78
-70.59
-75.447
12.805
-
16.973
Unknown
Vitamin C
Tablet -54.6
-46.96
-40.27
-47.277
7.170
-
15.167
Regression for Voltage vs. Concentration
SUMMARY OUTPUT
Regression Statistics
Multiple R
0.99917045
R Square
0.99834158
Adjusted R Square
0.99668316
Standard Error
2.0343244
Observations
3
ANOVA
df
SS
MS
F
Significanc
e F
Regression
1
2491.29397
6
2491.29
601.983
5
0.025933
Residual
1
4.13847578
3
4.13848
Total
2
2495.43245
2
Coefficients
Standard
Error
t Stat
P-value
Lower 95%
Uppe
95%
GF-AAS
12
Intercept
3.32376068
1.98147577
7
1.67742
0.34223
9
-21.85328
28.50
0.0002
-19577.436
797.927679
7
-24.535
0.02593
3
-29716.07
-943
RESIDUAL OUTPUT
Observation
Predicted -
3.48666666666667
Residuals
Standard
Residuals
1
-6.4649573
-
1.15170940
2
-0.8006
2
-26.042393
1.61239316
2
1.1209
3
-74.985983
-
0.46068376
1
-0.3203
Calculations:
magnitude
%rel error
m sdev
797.92768
0
-
19577.4359
-
4.07575171
7
b stdev
1.981476
3.32376068
4
% rel error tablet weight
0.62627
2
S stdev
7.17
-47.28
balanza
0.0004
% rel error w/w
8.50544
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
GF-AAS
13
8
10mL
0.02
10
0.2
100mL
0.08
100
0.08
w/w stdev
6.02875
8
s
magnitude
%rel error
for
subtracting
b: 7.43899721
7
-50.60
-
14.701451
divide by
slope
0.00021923
8
0.00258463
8.4823600
3
final relative stdev
8.48509467
5
0.00848509
5
final stdev
0.0384135
4
LOQ: ¿
10
×
(
sty
−
intercept stdev
slope
)
LOD
¿
3
×
(
sty
−
intercept stdev
slope
)
Questions:
1. Discuss the reliability of your findings and what you will do to improve this method. This results are very reliable because the technique of cyclic voltammetry is one of the most informative and accurate techniques to study redox reactions. Since we were studding a dietary supplement that is not regulated by the Food and drug administration the parameters of the concentration of their product are not as narrow as for products that are regulated by this agency so a ~10% of error is in the range of their acceptance concentration. This result is very reliable also because the concentration of the AAc in the tablet was inside of the calibration curve and was over the LOD and LOQ. It is important to notice that the calibration
curve was completely linear for the range that was study with a R
2
of .997 which means that the concentration of the tablet obtain is very reliable.
2. Based on the voltammetric results does the oxidation of AAc was reversible in your study?
GF-AAS
14
Base in the voltammograms that we acquired this oxidation was not reversible, this oxidation was completely irreversible. We concluded that the oxidation of ascorbic acid was completely irreversible because in the bottom part of the voltammogram there is a peak which is the peak when the acid donates electrons (oxidation) but in the upper part there is not a peak to show that the acid is accepting an electron again (reduction).
3. Based on the average oxidation potential AAc what would be the observed potential when a
SHE and calomel electrodes are used?
Since the oxidation potential for the AgCl electrode is 0.490V, with SHE the oxidation potential should be .073V and for SCE is should be 0.534V. (With respect to Ag electrode: SCE +.461 with SHE -0.417)
4. Does there was a difference in the precision and accuracy of the QC results vs. those of the unknowns? Explain
In this experiment we couldn’t do a Qc for a reactive limiting reason because our buffer pH 2.2 was completely used and the time left to analyzed the data was to short so we were not able to make and analyze a Qc sample. If we had done the Qc it was expected to be inside the calibration
curve and give a concentration very close to the one expected.
5. Why it is important to clean the working electrode between runs? It is important to clean the working electrode because the reaction of oxidation-reduction takes place in the surface of this electrode. The surface of this particular electrode which is made of glassy carbon gets saturated and to ensure the same conditions for each run the surface of the electrode has to be clean so the next reaction can take place again in the same surface. It is very important that the electrode is not saturated because if this happens it will get to a point where the electrode will not detect any more signal. References:
1.
1. Electroanalytical Chemistry. 2009. < http://www.aug.edu/~chmsam/Chemistry4840/ecchapter.pdf>
2.
2. Mayo Foundation for Medical Education and Research. Vitamin C (ascorbic acid), 2008. Web. 20 Aug. 2013. 08.
3.
Chem 333 Voltammetry CH 25, MSU 2007. < http://www.cem.msu.edu/~cem333/Week12.pdf >
GF-AAS
15
4.
De Jesus MA, Vera M, eta al. Instrumental Methods of Analysis Laboratory Manual. 2013
5.
Vitamin C Supplement. 2012. <http://umm.edu/health/medical/altmed/supplement/vitamin-c-ascorbic-acid>
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help
Related Documents
Related Questions
What are possible sources of error that may occur when performing a cyclic voltammetry experiment? How can they be improved? What are alternative methods of analysis?
arrow_forward
ll中国移动 4G
11:40 PM
© 1 26% O
electrochemistry homework
2. 简答题
Calculate the volume of hydrogen produced at r.t.p.
when a concentrated aqueous solution of sulfuric acid
is electrolysed for 15.0min using a current of 1.40A.
(F= 96500 Cmol-1; 1 mole of gas occupies 24.0 dm³
at r.t.p.)
输入答案
2/2
答题卡
提交
<上一题
(+
arrow_forward
(17,18-3,2) Select the most acidic hydrogen in the molecule below.
arrow_forward
Can you help me with the question please show work thank you very much
arrow_forward
One common way to determine phosphorus in urine is to treat the sample, after removing the protein, with Mo (VI) and then reducing the resulting 12-molybdophosphate complex with ascorbic acid to give an intense blue colored species called molybdenum blue. The absorbance of molybdenum blue can be measured at 650nm. A 24-hour urine sample was collected and the patient produced 1122mL in 24 hours. A 1.00mL aliquot of the sample was treated with Mo(VI) and ascorbic acid and diluted to a volume of 50.00mL. A calibration curve was prepared by treating 1.00mL aliquots of phosphate standard solutions in the same manner as the urine sample. The absorbances of the standards and the urine sample were obtained at 650nm and the following results obtained:
Solution Absorbance at 650nm:
1ppm P0.2302ppm P0.4363ppm P0.6384ppm P0.848Urine sample 0.518
How many grams of phosphorus were eliminated per day by the patient?
arrow_forward
explain the mechanism
arrow_forward
Calculate the absorbance of 0.00038 moles in 24.2 mL of solution given the molar absortivity is 1168 M-1 cm-1 and the path length is 0.6 cm.
Report your answer to 3 significant figures.
arrow_forward
Consider the galvanic series (shown below). From the choices provided below, please select the three metals or alloys that may be u
galvanically protect brass. Your possible choices are:
Cadmium, Copper, Silver, Titanium, Tin, Zine
Table 16.2 The Galvank Series
Platinuns
Gold
Graphite
Titanium
Shver
316 Stainlesa stoel (pamive)
304 Stainles steel (pamive)
Inconel (8IN-1JC-7) (pamive)
Nickel (passive)
Monel (70NI-C)
Incrcasingly inert (cathodic)
Copper-nickel alloy s
Bronzes (C-Sn alloys)
Copper
Brasses (Ce-Za alkoys)
Inconel (active)
Nickel (active)
Tin
Lead
316 Stainles stee (tive)
04 Stalnle stoel (tive)
Increasingly active (aodie)
Cast iron
Iroe and steel
Aluminum alleys
Camium
Carial pere aluminum
Zine Galv Ser
Magdremfagnesium alloys
Soevei M.G Foetana Corrosion Ergineering dedition Ceeright 1E by MGre a Boek
Company Reprinled wich permivicn.
Table 16.2
OJahn Wiley Sons Inc. All ghes ered
Save
arrow_forward
Write a one or two paragraphs of
-what was study in Introduction to Equilibrium Le Chateliers Principle
-Summarize what happened in these results shown below
-what results did this experiment end up with whether this lab was successful or not
arrow_forward
OCN-(aq) + OCI-(aq) → CO₂2-(aq) + N2(g) + Cl(aq) (basic media)
arrow_forward
4. The %Mn in steel can also be determined spectrophotometrically by oxidizing the
manganese to the intensely colored permanganate, MnO4-. Standard solutions of
permanganate gave the following absorbances (in a 1 cm cell):
ABSORBANCE
CONC. OF MnO4 (g/mL)
0.210
1.05 x 10-5
0.315
1.61 x 10-5
0.429
2.21 x 10-5
0.599
2.98 x 10-5
0.801
4.04 x 10-5
The following samples of steel were thoroughly reacted to convert the manganese into
permanganate and then diluted to 500.00 mL.
WT. OF STEEL (g)
ABSORBANCE
0.5886
0.611
0.3498
0.359
0.4555
0.482
Again using Excel, plot the calibration data and calculate the %Mn in the steel.
arrow_forward
calculate the [FESCN2+] using volumes of stock solutions. Presume that all of the
SCN- ions react. Next, record the light absorbance values of each standard
solution.
Volume
Volume
Volume
[FESCN2+]
Absorbance
Standard
Fe(NO3)3
SCN-
H2O
sample
(mL)
(mL)
(mL)
1
2.50
2.00
20.50
0.1811
2
2.50
1.50
21.00
0.3219
2.50
1.00
21.50
0.4981
4
2.50
0.50
22.00
0.6328
Stock [Fe(NO3)3] = 0.200 M, Stock [SCN-] = 0.0020 M.
%3D
arrow_forward
Chlorine pentafluoride
D (156) TESK - Green Sta
B Final assessmentpdf -
T Lab Reports - 202030
A www-awu.aleks.com/alekscgi/x/lIsl.exe/1o_u-IgNslkr7j8P3jH-lv-OZhvG1qYPWviNXOF96XoVW3_W7J0tF-2drAGbNSolpTW6rAkbtcy5PbEwUBck_5y4DIn88jVEEPfKWHKeGb8Pd1BB-lo?1oBw
Gmail
YouTube
A Home - SUNY Broo.
SUNY Broome Com.
= Calculus Preface (?)
E Brytwave Blackboard
O Clutch
Quizlet
Knowledge Check
Question 9
A student dissolves 14.9 g of potassium chloride (KCI) in 200. g of water in a well-insulated open cup. He then observes the temperature of the water fall from
20.0 °C to 15.2 °C over the course of 8.9 minutes.
Use this data, and any information you need from the ALEKS Data resource, to answer the questions below about this reaction:
KCl(s) → K (aq) + Cl (aq)
You can make any reasonable assumptions about the physical properties of the solution. Be sure answers you calculate using measured data are rounded to the
correct number of significant digits.
Note for advanced students: it's possible the…
arrow_forward
SEE MORE QUESTIONS
Recommended textbooks for you
Principles of Instrumental Analysis
Chemistry
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Cengage Learning
Chemistry: Principles and Practice
Chemistry
ISBN:9780534420123
Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Publisher:Cengage Learning
Related Questions
- What are possible sources of error that may occur when performing a cyclic voltammetry experiment? How can they be improved? What are alternative methods of analysis?arrow_forwardll中国移动 4G 11:40 PM © 1 26% O electrochemistry homework 2. 简答题 Calculate the volume of hydrogen produced at r.t.p. when a concentrated aqueous solution of sulfuric acid is electrolysed for 15.0min using a current of 1.40A. (F= 96500 Cmol-1; 1 mole of gas occupies 24.0 dm³ at r.t.p.) 输入答案 2/2 答题卡 提交 <上一题 (+arrow_forward(17,18-3,2) Select the most acidic hydrogen in the molecule below.arrow_forward
- Can you help me with the question please show work thank you very mucharrow_forwardOne common way to determine phosphorus in urine is to treat the sample, after removing the protein, with Mo (VI) and then reducing the resulting 12-molybdophosphate complex with ascorbic acid to give an intense blue colored species called molybdenum blue. The absorbance of molybdenum blue can be measured at 650nm. A 24-hour urine sample was collected and the patient produced 1122mL in 24 hours. A 1.00mL aliquot of the sample was treated with Mo(VI) and ascorbic acid and diluted to a volume of 50.00mL. A calibration curve was prepared by treating 1.00mL aliquots of phosphate standard solutions in the same manner as the urine sample. The absorbances of the standards and the urine sample were obtained at 650nm and the following results obtained: Solution Absorbance at 650nm: 1ppm P0.2302ppm P0.4363ppm P0.6384ppm P0.848Urine sample 0.518 How many grams of phosphorus were eliminated per day by the patient?arrow_forwardexplain the mechanismarrow_forward
- Calculate the absorbance of 0.00038 moles in 24.2 mL of solution given the molar absortivity is 1168 M-1 cm-1 and the path length is 0.6 cm. Report your answer to 3 significant figures.arrow_forwardConsider the galvanic series (shown below). From the choices provided below, please select the three metals or alloys that may be u galvanically protect brass. Your possible choices are: Cadmium, Copper, Silver, Titanium, Tin, Zine Table 16.2 The Galvank Series Platinuns Gold Graphite Titanium Shver 316 Stainlesa stoel (pamive) 304 Stainles steel (pamive) Inconel (8IN-1JC-7) (pamive) Nickel (passive) Monel (70NI-C) Incrcasingly inert (cathodic) Copper-nickel alloy s Bronzes (C-Sn alloys) Copper Brasses (Ce-Za alkoys) Inconel (active) Nickel (active) Tin Lead 316 Stainles stee (tive) 04 Stalnle stoel (tive) Increasingly active (aodie) Cast iron Iroe and steel Aluminum alleys Camium Carial pere aluminum Zine Galv Ser Magdremfagnesium alloys Soevei M.G Foetana Corrosion Ergineering dedition Ceeright 1E by MGre a Boek Company Reprinled wich permivicn. Table 16.2 OJahn Wiley Sons Inc. All ghes ered Savearrow_forwardWrite a one or two paragraphs of -what was study in Introduction to Equilibrium Le Chateliers Principle -Summarize what happened in these results shown below -what results did this experiment end up with whether this lab was successful or notarrow_forward
- OCN-(aq) + OCI-(aq) → CO₂2-(aq) + N2(g) + Cl(aq) (basic media)arrow_forward4. The %Mn in steel can also be determined spectrophotometrically by oxidizing the manganese to the intensely colored permanganate, MnO4-. Standard solutions of permanganate gave the following absorbances (in a 1 cm cell): ABSORBANCE CONC. OF MnO4 (g/mL) 0.210 1.05 x 10-5 0.315 1.61 x 10-5 0.429 2.21 x 10-5 0.599 2.98 x 10-5 0.801 4.04 x 10-5 The following samples of steel were thoroughly reacted to convert the manganese into permanganate and then diluted to 500.00 mL. WT. OF STEEL (g) ABSORBANCE 0.5886 0.611 0.3498 0.359 0.4555 0.482 Again using Excel, plot the calibration data and calculate the %Mn in the steel.arrow_forwardcalculate the [FESCN2+] using volumes of stock solutions. Presume that all of the SCN- ions react. Next, record the light absorbance values of each standard solution. Volume Volume Volume [FESCN2+] Absorbance Standard Fe(NO3)3 SCN- H2O sample (mL) (mL) (mL) 1 2.50 2.00 20.50 0.1811 2 2.50 1.50 21.00 0.3219 2.50 1.00 21.50 0.4981 4 2.50 0.50 22.00 0.6328 Stock [Fe(NO3)3] = 0.200 M, Stock [SCN-] = 0.0020 M. %3Darrow_forward
arrow_back_ios
SEE MORE QUESTIONS
arrow_forward_ios
Recommended textbooks for you
- Principles of Instrumental AnalysisChemistryISBN:9781305577213Author:Douglas A. Skoog, F. James Holler, Stanley R. CrouchPublisher:Cengage Learning
- Chemistry: Principles and PracticeChemistryISBN:9780534420123Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward MercerPublisher:Cengage Learning
Principles of Instrumental Analysis
Chemistry
ISBN:9781305577213
Author:Douglas A. Skoog, F. James Holler, Stanley R. Crouch
Publisher:Cengage Learning
Chemistry: Principles and Practice
Chemistry
ISBN:9780534420123
Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Publisher:Cengage Learning