Ana Chem LAB Flashcards
(95 cards)
1
Q
What is potentiometric titration?
A
A method involving graphing the volume of titrant added against the voltage change (or pH) in the solution being titrated.
2
Q
What indicates the equivalence point in potentiometric titration?
A
A sharp pH change.
3
Q
What types of reactions can potentiometric titration be used for?
A
- Acid-base reactions
- Redox reactions
- Precipitation reactions
- Complex formation reactions
- Non-aqueous systems
4
Q
How does potentiometric titration compare to visual indicator titrations?
A
It achieves comparable speed and often enhanced accuracy.
5
Q
What is the role of the reference electrode in potentiometric titration?
A
It maintains a constant potential.
6
Q
What is the function of the indicator electrode?
A
Its potential depends on the reactants or products in the reaction.
7
Q
What are common electrodes used in potentiometric titration?
A
- Calomel (reference)
- Glass (indicator)
8
Q
What should be included in titration curves?
A
The entire data set, emphasizing the point of maximum slope.
9
Q
How can accuracy be improved when identifying the equivalence point?
A
By creating a detailed graph extending 1-2 mL before and after the actual equivalence point.
10
Q
What are key sources of error in potentiometric titration?
A
- Failing to draw a smooth curve
- Inaccuracies in pinpointing the inflection point
11
Q
What is the significance of the half-equivalence point?
A
It indicates equal concentrations of the acid (HA) and its conjugate base (A-).
12
Q
How can pKa be estimated?
A
As the pH of the solution at the half-equivalence point.
13
Q
What is a common discrepancy when comparing experimental pKa values?
A
Differences between molar concentrations and activities in equilibrium expressions.
14
Q
What does the first derivative of the titration curve identify?
A
The equivalence point as the maximum on the plot.
15
Q
How does the second derivative aid in equivalence point determination?
A
It refines the identification by plotting the rate of change of the first derivative.
16
Q
What caution should be taken when using derivative methods?
A
They may accentuate noise in the data.
17
Q
What information aids in identifying unknown acids?
A
- Collected equivalence volumes
- pKa values
18
Q
What complication arises when identifying unknown acids?
A
The unknown acid may be monoprotic or diprotic, complicating identification if pKa values are close together.
19
Q
What does the calculated molecular weight reflect for diprotic acids?
A
It will be half of the actual molecular weight.
20
Q
What initial measurements must be recorded in the experimental procedure?
A
Initial pH measurements of the solution.
21
Q
How should NaOH be administered near the equivalence point?
A
In smaller increments of 0.20 mL.
22
Q
What must be done after observing the curve flatten post-equivalence?
A
Larger increments of NaOH may again be introduced.
23
Q
What must be adhered to during waste disposal?
A
Safety protocols.
24
Q
What should be done with all relevant data?
A
Collect it meticulously in a notebook for submission.
25
What software can be used to plot titration curves?
Excel.
26
What types of plots must be created for thorough analysis?
* Derivative plots (first)
* Derivative plots (second)
27
How is the unknown acid identified?
By comparing experimental values with literature values.
28
What reaction is utilized for sensitive iron determination?
The reaction between iron(II) and 1,10-phenanthroline to create a red complex
29
What is the molar absorptivity of the Fe-phenanthroline complex?
11,000 at a wavelength of 508 nm
30
What pH levels do not affect the color intensity of the Fe-phenanthroline complex?
pH levels between 2 and 9
31
What oxidation state must iron be in for the determination method?
+2 oxidation state
32
What reducing agent is commonly used in the iron determination method?
Hydroxylamine hydrochloride
33
What law applies to the iron determination method?
Beer's Law
34
What is the main objective of the experiment in activity 2?
To quantitatively determine the mass of iron in dietary supplement tablets
35
How should red solutions containing the Fe-1,10-phenanthroline complex be disposed of?
In designated containers
36
What is the preparation method for a 0.1% 1,10-phenanthroline solution?
Dissolve 0.1g in 100mL distilled water
37
What is the concentration of hydrochloric acid prepared in the experiment?
6M
38
How is the ferrous ammonium sulfate solution prepared?
Weigh 0.0700g, dissolve in water, and dilute with 2.5mL of 3M sulfuric acid to prepare a solution containing 100mg Fe/mL
39
What is the first step in the sample preparation process?
Weighing five tablets of the dietary supplement
40
What is the purpose of grinding the tablets?
To obtain a fine powder for efficient extraction of iron
41
What solution is added to the powdered sample for digestion?
25 mL of 6M hydrochloric acid
42
What is the purpose of filtering the solution after digestion?
To separate any undissolved residue from the liquid
43
What is the final labeling for the collected solution after filtration?
'Stock sample solution'
44
What is added to the sample solution to convert Fe³⁺ to Fe²⁺?
Hydroxylamine Hydrochloride
45
What is the optimal pH range for the reaction to occur effectively?
Between 6 and 9
46
What is the final volume to which the sample solution is diluted in act 2?
10 mL
47
What is measured using a UV-VIS spectrophotometer?
The absorbance of the resulting solution
48
What is used to determine the concentration of iron in the diluted sample?
The linear regression equation from the calibration curve
49
What is calculated to find the mass of iron per tablet?
The total mass of iron in the stock solution divided by the number of tablets
50
What is the first step in the determination of iron in dietary supplements?
Preparation of the Sample: A known volume of the sample stock solution (200 µL) is transferred into a 10-mL volumetric flask. This sample is derived from the previously prepared stock solution, which contains the digested iron from the supplement tablets.
51
What reagents are added to the sample in the volumetric flask?
- Hydroxylamine Hydrochloride (500 µL): This reducing agent converts Fe³⁺ to Fe²⁺.
- Sodium Acetate (800 µL): Buffers the solution to maintain a pH of 6-9.
- 1,10-Phenanthroline Solution (1000 µL): Reacts with Fe²⁺ to form a red [Fe(phen)₃]²⁺ complex.
52
What is the purpose of Hydroxylamine Hydrochloride in the determination of iron?
Hydroxylamine Hydrochloride is a reducing agent that converts iron from the +3 oxidation state (Fe³⁺) to the +2 oxidation state (Fe²⁺).
53
Why is Sodium Acetate added during the analysis?
Sodium Acetate buffers the solution to maintain an appropriate pH (between 6 and 9), which is essential for the stability and formation of the iron-phenanthroline complex.
54
What does 1,10-Phenanthroline Solution do in the determination of iron?
1,10-Phenanthroline reacts with Fe²⁺ ions to form a stable red complex, [Fe(phen)₃]²⁺, which is the basis for the spectrophotometric measurement.
55
After adding the reagents, what steps are taken before measuring absorbance?
The solution is diluted to the final volume of 10 mL and allowed to stand for five minutes to ensure the reaction between iron and 1,10-phenanthroline goes to completion.
56
At what wavelength is the absorbance measured, and why?
The absorbance is measured at the wavelength corresponding to the maximum absorbance (λmax) obtained from the standard solutions, as this provides the most accurate results.
57
How is the absorbance data analyzed to determine iron concentration?
The absorbance data is used in conjunction with a calibration curve created from standard iron solutions. Beer’s Law allows determination of the concentration of iron in the diluted sample based on its absorbance.
58
What is the final step in calculating the amount of iron in the dietary supplement?
The concentration of iron in the diluted sample is back-calculated to find the concentration in the original stock solution. The mass of iron in the stock solution is then calculated to determine the amount of iron per tablet.
59
Why is this spectrophotometric method reliable for determining iron content?
This method is sensitive and reliable, allowing for accurate determination of iron levels, which is crucial for assessing the nutritional value of dietary supplements.
60
What does the photometric titration method involve?
The photometric titration method involves studying metal ions by using a ligand, EDTA (Y4), to bind with a metal (M) in solution.
61
How is the equivalence point of a titration determined in photometric titration?
The concentration of the metal is held constant while the amount of ligand is varied to determine the equivalence point of a titration.
62
What kind of plot is produced in photometric titration, and what does the intersection indicate?
A straight-line plot with different slopes is produced, and the intersection of these lines indicates the amount of titrant needed at the equivalence point.
63
What is the reaction equation for the titration experiment?
H2Y2 + Cu²⁺ ⇌ CuY²⁻ + 2H⁺.
64
What does HY2 refer to in the reaction equation?
HY2 refers to Na₂H₂Y, which is the disodium salt of EDTA.
65
At what wavelength is the titration conducted, and why?
The titration is conducted at a wavelength of 625 nm, since both copper (II)-EDTA complex and copper (I) ion absorb at this wavelength, but the complex has a much higher molar absorptivity.
66
Why is it crucial to correct absorbance values during the titration?
It is crucial to correct absorbance values for volume changes due to titrant additions to ensure accurate endpoint determination.
67
What does a plot of absorbance versus EDTA volume indicate near the endpoint?
A plot of absorbance versus EDTA volume shows deviations in the endpoint region, indicating incomplete reaction at the equivalence point.
68
What happens to absorbance after the equivalence point?
After the equivalence point, added titrant leads to dilution, causing a slight decrease in absorbance.
69
Why is maintaining a pH between 2.4 and 2.8 important during the titration?
Maintaining a pH between 2.4 and 2.8 using an acetate buffer is essential to avoid significant changes in the effective binding constant of EDTA with metal ions.
70
What does the low pH allow for during the titration?
The low pH also allows for the titration of copper in the presence of other metal ions that have weaker complexation with EDTA.
71
What reagents are required for the photometric titration?
Reagents include 0.015M EDTA, acetate buffer at pH = 4.00, and an unknown Cu(II) solution.
72
What laboratory equipment is needed for this experiment?
Necessary laboratory equipment includes pipettes, micropipettes, aspirators, UV-VIS spectrophotometer, and 10 mL test tubes.
73
How is 0.015M EDTA prepared?
To prepare 0.015M EDTA: Dissolve 1.3959 g of EDTA disodium salt in distilled water and dilute to 250 mL.
74
How is the acetate buffer prepared?
For the acetate buffer: Prepare a 0.1 M acetic acid solution, adjust pH to 4.00 with sodium acetate.
75
What is the source of the unknown Cu(II) solution?
The unknown Cu(II) solution will be provided during the lab session.
76
How are the test tubes prepared for the titration?
Using a 1000 µL micropipette, transfer 500 µL of the Cu(II) solution into ten test tubes, then add 1.5 mL of acetate buffer to each and swirl.
77
What does Table 1.0 specify about the test tube setup?
The volume of EDTA and water added to each test tube is specified in Table 1.0, which outlines various reagent volumes.
78
What does the example setup of test tubes include?
Example for the setup of test tubes includes combinations of Cu(II), buffer, EDTA, and water with resulting absorbance values ranging from 0.00 to 5.00.
79
What is quantitative fluorescence analysis applicable for?
Quantitative analysis is applicable for both excitation and emission spectra, facilitating high accuracy through appropriate methods.
80
What are the methods used in quantitative fluorescence analysis?
Methods include one wavelength calculation, two wavelength calculation, and three wavelength calculation, which is selected based on the sample type.
81
What is the primary compound of interest in the experiment?
The experiment focuses on analyzing a solution of Rhodamine B, which serves as the primary compound of interest.
82
What are the required reagents for Rhodamine B analysis?
Required reagents include a 100 ppm Rhodamine B stock solution for the class and 1 ppm Rhodamine B solutions for individual groups.
83
What are the key procedural steps in Rhodamine B fluorescence analysis?
Key procedural steps involve peak searching for Rhodamine B, capturing excitation and emission spectra, preparing standard solutions at various concentrations, measuring fluorescence intensity, and preparing a calibration curve to determine unknown concentrations.
84
What are the specific tasks in the Rhodamine B analysis?
Specific tasks include performing three measurement cycles for each standard concentration and assessing the unknown Rhodamine concentration after calibration.
85
What is the process for determining the excitation wavelength?
First, determine the excitation wavelength. This is the shorter wavelength range. (Note: set the lambda_Em higher than the highest range.)
86
What is the process for determining the emission wavelength?
Determine the emission wavelength, which has a longer wavelength range. But, set the lambda_ex as shorter than the lowest range.
87
How is fluorescence intensity measured in Rhodamine B analysis?
Measure the fluorescence intensity by pressing 'Measure 6' and set each wavelength for Em and Ex. Perform 3 cycles per standard concentration.
88
Why do magnesium ions fluoresce when complexed with 8-hydroxyquinoline?
Magnesium ions in isolation do not exhibit fluorescence; however, upon complexation with 8-hydroxyquinoline in an alcohol solution, they display fluorescence at specified excitation and emission wavelengths (Xex 420 nm and Aem 530 nm).
89
What is the procedure for preparing Mg²+ solutions for fluorescence analysis?
The procedure begins with the preparation of various volumes of 10 ppm Mg²+ solutions mixed with 100 ppm 8-hydroxyquinoline.
90
How are excitation and emission wavelengths determined for Mg²+ fluorescence analysis?
Excitation and emission wavelengths need to be determined by scanning the highest concentration standard solution, with Xex and Xem recorded for further analysis.
91
What is the purpose of preparing a calibration curve in fluorescence analysis?
The calibration curve plots fluorescence intensity against Mg²+ concentration and helps quantify the concentration of an unknown Mg²+ solution.
92
What are the final steps in Mg²+ fluorescence analysis?
Final steps include calculating the regression coefficient, determining the slope and equation of the calibration line to evaluate the linear relationship between fluorescence and concentration, and quantifying the concentration of an unknown Mg²+ solution using the established curve.
93
Why is determining the excitation spectrum important?
The excitation spectrum helps identify the optimal wavelength for exciting a given fluorescent compound, enhancing measurement accuracy.
94
What is the difference between excitation wavelength (Xex) and emission wavelength (Xem)?
Excitation wavelength (Xex) is the specific wavelength utilized to stimulate fluorescence, while emission wavelength (Xem) is the wavelength at which the emitted fluorescence is detected.
95
Why is evaluating fluorescence intensity for both the sample and the blank important?
Evaluating fluorescence intensity for both the cell (sample) and the blank is crucial for establishing a baseline measurement, ensuring reliability, and minimizing potential interference from environmental variables or contaminants.
