Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
681
questions
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0answers
14 views
FTIR Michelson Interferometer [on hold]
Calculate the change in path length (x) in the Michelson Interferometer required for total interference. (sum = 0) for 200 cm-1.
0
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0answers
9 views
How can I make a reference humidity environment with NaOH pellets?
I have NaOH pellets at my disposal. Some of the pellets are degraded, but most are not, and I can provide a new batch if needed.
I would like to test several humidity sensors in an environment with a ...
1
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1answer
40 views
Winkler's method in the absence of iodide
I'm currently doing an IB chemistry individual investigation on the effect of adding bleach to water on the water's dissolved oxygen content. I've used Winkler's method for this and I'm just wondering ...
9
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3answers
500 views
How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?
Question 3:
It said $m/z = 122,$ and $m/z = 124$ is in a $3:1$ ratio, so I figured that meant that chlorine is present. Then I thought $m/z$ was the actual compound's molecular mass.
So I used ...
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0answers
17 views
How can I calculate molar concentration from a precipitate? [closed]
In a sample of water, $V=\pu{1000 mL}$, I found the concentrations of $\ce{Mg^2+}$ and $\ce{Ca^2+}$ ions that cause the hardness of the water. Then added enough $\ce{Na2CO3}$ to get $\ce{MgCO3}$ and $\...
4
votes
1answer
283 views
Calcium ion and sulfate did not form precipitate
I was in the chemistry lab earlier this week. We were doing a qualitative experiment (no concentration given for any solution).
I added an unknown solution that contains $\ce{Ba^2+},$ $\ce{Ca^2+},$ ...
1
vote
1answer
73 views
Preparation of acetate buffer from sodium acetate and hydrochloric acid
A $\pu{1.0 L}$ buffer solution of $\mathrm{pH}~4.43$ is made up of $\pu{0.30 M}$ sodium ethanoate and $\pu{0.20 M}$ $\ce{HCl}$ solutions. Calculate the volume of sodium ethanoate and $\pu{0.20 M}$ $\...
0
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0answers
21 views
Can the presence of radon (Rn-222) be determined by testing dust?
If a relatively unventilated area, like a basement, were to be exposed to radon gas (Rn-222), would the dust in the area possess a detectable amount of lead? Considering lead 214 is a decay product of ...
0
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1answer
37 views
When will the Lassaigne's method for detection of nitrogen and Kjeldahl's method for quantitative estimation of nitrogen fail?
Lassaigne's method:
The organic compound is fused with dry $Na$ in a fusion tube. The fused mass after extraction with water is boiled and filtered. This filtrate is called sodium extract (S.E.), ...
0
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0answers
23 views
Use of a top-loading balance
When a weight measurement enters directly into the calculation of a quantitative analysis result that is to be reported in a four significant figures, is an ordinary top loading balance satisfactory ...
0
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0answers
25 views
Is it possible to skip H2S completely for group III cation (or beyond) identification?
Group I cation identification (group I) requires dilute $\ce{HCl}$ to precipitate. If the centrifugate (product of centrifuge that does not precipitate) resulted, then we move to group II. Group II ...
0
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1answer
43 views
SO3 in wood ash
I have seen several sources note that wood ash typically contains 3–4 % $\ce{SO3}$ by weight. My question is, why would ash have any $\ce{SO3}$? $\ce{SO3}$ boils at 45 °C, so it should have all boiled ...
4
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0answers
39 views
CuAAC “Click” reaction giving inconsistent results
I apologize in advance for the large amount of text and thank all those who take the time to read it.
The "Click" reaction after Fokin and Sharpless is known to achieve high yields without long ...
0
votes
1answer
62 views
How do I explain the existence of these 2 peaks in this mass spectrometry?
Question about HRMS:Phosphatidylcholines and phosphatidylethanolamines are common types of glycerophospholipids found in biological membranes. Because of the high amount of heteroatom content, ...
0
votes
2answers
75 views
Could dimerization account for weak IR signals?
How would you interpret the IR spectrum of your product if it's peaks match the literature spectrum, but the signals are weak? Could the argument that the sample was very dilute and lots of water was ...
4
votes
1answer
83 views
Timescales in Chemical Analysis
Has anyone seen a comparative list of typical run times of the techniques used in analytical chemistry? I am making a list of rough timescales of analytical techniques (for a slide). Assume that the ...
0
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0answers
30 views
BOD5 respirometric method
I operate in a wastewater treatment plant laboratory and I use respirometric method for BOD5 measurement (hach direct plus). Recently I am obtaining high value for BOD (biological oxygen demand) for ...
2
votes
1answer
40 views
In Flame Emission Spectroscopy, what part of the flame is used to measure the concentration of the analyte?
Flame Emission Spectroscopy is an analytical measuring device that relates the intensity of the emitted light relative to to the concentration of the sample.
As I am reading an article about FES, I ...
1
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1answer
23 views
Organic solvent for cleaning autosampler syringe
I work in a laboratory where gas chromatography is used extensively. We handle phthalates. What are the possible wash solvent for autosampler syringe? I've been using acetone.
6
votes
4answers
578 views
accurate measurement from inaccurate tools [closed]
It is a very general question. Is there a good way to systematically increase the accuracy and precision of a measuring tool using only mathematical means? For example, average 10 measurements can ...
20
votes
2answers
2k views
Why does the weaker C–H bond have a higher wavenumber than the C=O bond?
My understanding is that a stronger bond has a higher wavenumber in IR spectrum. But why does the C–H vibration have a higher wavenumber than the C=O vibration? The latter is a double bond, so I think ...
3
votes
1answer
33 views
HPLC Columns For Compounds Not Soluble In Non- Or Low Polar Solvents [closed]
Can someone recommend HPLC columns for compounds which are not soluble in no- or low polar solvents (hexane, isopropanol, toluene, and dichloromethane)?
3
votes
1answer
90 views
Choosing LC-MS modifier - why only acids?
During method selection our chromatographists have options like NH4, TFA, Formic Acid. What's the point of choosing only between acid? Why not use the strongest that guarantees ionization? The sample ...
16
votes
6answers
5k views
Is there a commercial liquid with refractive index greater than n=2?
For an application I need a commercial, transparent liquid with refractive index $n>2$.
Is this kind of liquid available?
What's the chemical composition of this?
On the web, only $n=1.81$ is ...
1
vote
0answers
29 views
Determining the composition of basic copper sulfate by titrimetry
A colleague shared an undergraduate level classical gravimetry/titrimetry experiment on determining the stoichiometry of basic copper sulfate. I am looking for a reference for this type of experiment. ...
3
votes
0answers
29 views
Ethyl acetate produces red colour on ceric ammonium nitrate test
When I did CAN test on ethyl acetate red colour was seen. I thought water may get added with Ethyl acetate to produce
this compound which in turn gave red coloration but carbon should not make three ...
1
vote
2answers
56 views
Can I normalize my data in order to compare it?
I have three chromatograms of the same eluted protein but at different concentrations, since it got diluted during purification process) and hence peak maximums at very different absorbances.
The ...
2
votes
0answers
33 views
Increasing concentration of acetylcholine via SPE
I am trying to increase the final yield of acetylcholine (ACh) in my biofluid samples. I need to get the yield high enough for high confidence annotation of ACh (currently all I can really say is that ...
2
votes
1answer
29 views
What is the equation for solving the concentration of the unknown from a Single-point Standard Addition Calibration for Potentiometry?
I know how to use the standard addition equation for a single-point analysis from an equation I got from the Analytical Chemistry book "Quantitative Chemical Analysis" 9ed by D. Harris.
However, ...
3
votes
1answer
58 views
Which compounds react positively in the aniline dye test?
I read that to test for the presence of phenol groups in an organic compound the aniline dye test can be performed. If the solution has phenol present it gives a red or orange precipitate to confirm ...
2
votes
0answers
39 views
What instrument is used to detect heavy metals? [closed]
If i have blood sample, organ tissue sample or food sample, what analytic technique is used in laboratory to detect the ppm levels of heavy metals? What electronic intrument they use?
9
votes
2answers
848 views
What are the limitations of the Hendersson-Hasselbalch equation?
Our instructor told us that prior to the equivalence point, the $\mathrm{pH}$ of a solution is dependent on the HH equation. However, when I tried practicing for polyprotic acid titration, I came upon ...
1
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1answer
74 views
Is the cathode and anode on the cell notation of an Electrolytic cell on the same side as if how you will write it for a Galvanic cell?
I was reading an online material then I came upon a cell notation for an electrolytic cell (I determined that it was an electrolytic cell because of the absence of a salt bridge). Usually, I will ...
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1answer
15 views
How many calcium ions is needed to displace hydronium ions in an strong acid ion exchange resin?
If 1 mole of Ca2+ can displace 2 moles of Na+ in an ion exchange resin, can it do the same for H+? Will Ca2+ ion displace 2 moles of H+ in a strong acid resin?
0
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0answers
23 views
How can I calculate for the theoritical potential needed to precipitate a metal in an electrolytic cell?
We were given a problem where we are to calculate the theoretical potential needed to initiate the deposition of $\ce{Cu^2+}$ in a solution buffered to $\mathrm{pH} = 4.00$ and the IR drop associated ...
1
vote
1answer
33 views
Why do impacting electrons have a low probability of causing ionization?
In a section on ionization efficiency and ionization cross section, my mass spectrometry textbook, Mass Spectrometry by Jürgen Gross [1, pp. 38–39], says the following:
The ionization energy ...
1
vote
1answer
42 views
What is the correct equation for calculating the electric potential of an electrochemical cell?
When I'm studying electrochemistry, we were given an equation that all chemistry students are familiar with, which is:
...
7
votes
1answer
126 views
In the last step of Kjeldahl Method, is the reaction of ammonium to NaOH not taken into account?
In the last step of Kjeldahl method, the unreacted $\ce{HCl}$ in the solution is back titrated with a standard $\ce{NaOH}$ and the concentration of $\ce{HCl}$ that has been used to neutralize the ...
0
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1answer
43 views
What causes positive and negative deviations when weighing analytical samples?
Positive deviations are when the measured mass is more than the true mass of the sample and negative deviations are when the measured mass is less than the true mass of the sample. What steps causes ...
1
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1answer
181 views
Why do we use hydrochloric in the test for sulfate ions but nitric acid for halide ions?
Recently, I have learnt about testing for ions in qualitative analysis (BBC Bitesize).
The link above which I used for reference mentions that for the test for sulfate anions, hydrochloric acid $(\ce{...
0
votes
1answer
47 views
How can spike recovery be over 100%?
I am confident enough about my knowledge about spiking and the process of standard addition but I came across this process which claimed to have a percent recovery of 115% and it was considered as a ...
8
votes
1answer
933 views
Strange batch of potassium nitrate with lower than expected melting point
I'm part of a rocket building team and I'm working with propellants. We use saltpeter as the oxidizer, bought as fertilizer and purified by recrystallization. Recently we bought it from another source,...
2
votes
1answer
66 views
Test for unsaturation
Ethene and ethyne can be distinguished by employing the test
a. $\ce{Br2}$ in organic solvent
b. Baeyer's test
c. Phenyl hydrazine
d. Tollen's reagant
According to me it ...
-1
votes
1answer
51 views
To how much significant figures do I reduce my absolute uncertainty if it has more significant figures than my measurement?
They say that the absolute uncertainty in my measurement should always be reduced to 1 significant figure but I don't understand why.
0
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0answers
39 views
Using concentrated sulfuric or nitric acid during titration of permanganate with oxalic acid
During titration of $\ce{KMnO4}$ with $\ce{H2C2O4}$, can we use concentrated $\ce{H2SO4}$ or $\ce{HNO3}$ instead of bench sulfuric acid?
1
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0answers
30 views
Protein purification pressure limits confusion, about the X-MPa limit for FPLC?
I have always been a bit confused about column pressure limits. I have to elaborate a bit on the problem to get to my question:
In protein purification we use the äkta purification machines (e.g. ...
1
vote
2answers
55 views
Calculating amount of base needed to achieve a specific pH in a mixed ethanol-water solvent
I'm looking for some way to calculate how much base I will need to add to an unbuffered solvent consisting of a mixture of ethanol and water in order to basify it to a specific reading (10) on an a pH ...
0
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0answers
12 views
Positive or negative error using FAAS
if we want to determine the quantity of zinc in an insulin formulation, we make standard solutions for the measurements and we also have the physical samples. In standard solutions it contains water, ...
19
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2answers
2k views
Does ultrasonic bath cleaning damage laboratory volumetric glassware calibration?
As an analytical chemist, I'm always ensuring my glassware is thoroughly clean before I start an analysis. However, my supervisor always states that using ultrasonic bath to clean volumetric glassware ...
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0answers
31 views
Calculating Sensitivity in Mass Spectrometry
My mass spectrometry textbook gives the following example:
Calculating sensitivity Magnetic sector instruments are specified to have a sensitivity of about $4 \times 10^{-7} C \ \mu g^{-1}$ for the ...
