Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
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Inductively Coupled Plasma and Mass Spectrometry
I was doing some homework and I was reading about how ICP is suitable for mass spectrometry and it said how its high temperature favours ionization which is good in MS. But also, because the ...
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1answer
58 views
XRF is “non-destructive,” but what actually happens to the sample?
Editing for clarity and more details.
My colleague has been using XRF to quantitatively analyze 47-mm diameter Teflon membrane filters for metals, minerals, and rare earths. Much of their analysis ...
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30 views
What substance is shown in this NMR spectrum? [closed]
Does anybody know what substance is shown in this NMR spectrum?
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Is the method for the measurement of free fatty acid content for oleic oil the same as other edible oils? [closed]
I know of a method to measure FFA content for oleic oil. But I'd like to measure FFA content of
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1answer
54 views
Difference between the terms “analyte” and “analyate” and their applicability
“Analyte” is the term that is usually universally understood and is listed in IUPAC Gold Book:
analyte The component of a system to be analysed.
However, recently I stumbled upon the word “...
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2answers
21 views
What is the purpose of atomisation in atomic absorption spectroscopy? [closed]
What is the purpose of the atomisation process in atomic absorption spectroscopy?
I understand that solution is evaporated by the flame and then the molecules decompose into atoms.
But why must the ...
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0answers
37 views
Calculate the percent composition of a sodium carbonate/sodium bicarbonate mixture
In a lab, we titrated a solid mixture of sodium carbonate and sodium bicarbonate with $\pu{0.1 M}\ \ce{ HCl}$. We are asked to calculate the percent composition by mass of sodium carbonate and sodium ...
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22 views
Activity-Corrected pH Problem [closed]
I am trying to solve this problem for the activity corrected pH. It reads:
You have a solution that is 6 mmol H2SO4 (Ka2 = 0.011)and 4 mmol of Na2HPO4 (Ka1 1.1e-2, Ka2 7.5e-8, Ka3 4.8e-13). Calculate ...
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3answers
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Do the procedure used to find the empirical formula from combustion analysis be extended in other cases when is not specifically mentioned?
The situation is as follows:
A sample of $\pu{19.40 g}$ from a certain compound consisting only in $\ce{K, Cr}$ and $\ce{O}$, receives a treatment. This gives $\pu{7.6 g}$ of $\ce{Cr2O3}$ and $\pu{...
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1answer
40 views
How does a mass spectrometer treat ions? [closed]
I always thought that in a mass spectrometer all the ionized fragments were going in the quadrupole at the same time, and then this quadrupole was sorting them by ratio.
But last week I learn that a ...
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1answer
17 views
How do I scale up to semi-prep from an analytical HPLC [closed]
I am looking for an equation that would allow me to change the variables injection volume, column size, and flow rate scaling up from an analytical HPLC to a semi prep instrument.
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30 views
How to clean pocket pH meter before storage?
Hello.
I read about different methods how to clean this specific(attached photo)pocket pH meter before storage and i can't figure out what is the right way.
One method says to stir the pH meter(...
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Can chloride concentration be measured as CaCO3 mg/l
I work in a chemical analysis lab.
today I received a sample from a client who wants chloride concentration expressed as ppm of CaCO3.
I suspect it's a mistake but I am not sure if there is any ...
2
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1answer
80 views
How is antioxidant activity of carotenoids determined?
I am doing some research regarding carotenoids and beta-carotene. After extracting the sample, I have not been able to find a way to measure antioxidant activity of beta-carotene. I have $\pu{0.1mM}$ ...
2
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1answer
80 views
How can one determine an atomic mass with high accuracy using gravimetric analysis?
In the Wikipedia article on gravimetric analysis it is said that gravimetric analysis was used to determine the atomic masses of many elements in the periodic table to six figure accuracy. There are, ...
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1answer
49 views
Determining structure from C-NMR spectrum, is my answer correct?
Determine the structure of the compound whose spectral data is given below and explain your reasoning (5 marks for structure, 15 marks for reasoning). The peak at 7.27 ppm does not belong to the ...
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1answer
67 views
Which chemical is used in drunken driver test?
Which chemical is used in drunken driver test?
Acidified K2Cr2O7
KMnO4
Chromyl Chloride
H2O2
On searching on Google, I got the answer as option 1, acidified potassium ...
4
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1answer
98 views
Crystal structures of heaviest nuclides' compounds
What is the heaviest element of the periodic table for which there is a compound whose crystal structure has been completely resolved by X-ray diffraction?
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29 views
Home test for the presence of sugar in erythritol
Is there a test to distinguish erythritol from sugar at home without expensive lab equipment or exotic reagents? Sometimes I purchase erythritol online and wonder if it's been diluted with sugar.
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What does it mean to have coupling in H-NMR spectra? [duplicate]
That's the thing I didn't really get about NMR. By coupling, are the hydrogens coupled in that they split each other?
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1answer
52 views
When disolving a iron pill for titration, why do I use sulfuric acid instead of nitric or hydrochloric acid?
In a titration to decide the iron content of a pill we dissolved the iron in sulfuric acid and then titrated it with cerium(IV) sulfate. But I just wondered what's wrong with using nitric and ...
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2answers
84 views
Why does not aqua regia burn filter paper?
We were doing basic radical analysis in lab and we were asked to add aqua regia on the filtered PPT collected on the filter paper and collect the formed solution , my question is if aqua regia can ...
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3answers
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Am I using these spectra to identify the compound correctly?
What is the structure of the molecule whose data is shown below? Explain your answer [...] EI mass spectrum: The highest peak observed is $m/z$ 210 and its abundance is low. The only other significant ...
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3answers
221 views
How is the distance between m/z axis values in mass spectrums called?
The output data of mass spectrometers is relative intensity (y axis) over m/z (x axis). How is the distance between m/z values on the x-axis called (in case of centroided data and profile/raw data ...
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1answer
42 views
Determining the hydrogen peroxide content in acetic acid [closed]
For a project I have to determine the peroxide content in some samples, for which we plan to use glacial acetic acid. Unfortunately, I don't know the peroxide content of my acetic acid and because we ...
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38 views
Analytical Organic Chemistry - Do you agree with my answer to this C-13 NMR question? [closed]
Question 2b:
Because of the 184.7 signal, I think it's either an ester or carboxylic acid. There isn't a DEPT signal based on 184.7 because the carbon is not bonded to any hydrogens. Since there ...
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1answer
47 views
Qualitative determination of the presence of cations [closed]
In "Introduction to Analytical Chemistry" I have been asked to propose various tests and chemical methods to determine whether a sample contains a series of metallic cations.
These metallic cations ...
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1answer
48 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 ...
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3answers
536 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 ...
4
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1answer
318 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 $\ce{Ba^2+},$ $\ce{Ca^2+},$ ...
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1answer
115 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 $\pu{0.20 M}$ $\...
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22 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 ...
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1answer
48 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.), ...
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35 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 ...
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0answers
28 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 ...
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1answer
47 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 ...
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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 ...
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1answer
67 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, ...
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2answers
78 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
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1answer
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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 ...
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33 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
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1answer
48 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 ...
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1answer
31 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.
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4answers
613 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
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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
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1answer
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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
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1answer
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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 ...
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6answers
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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 ...
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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. ...
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0answers
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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 ...
