Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
658
questions
3
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1answer
60 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
5answers
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
24 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
15 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
50 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
28 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
24 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, ...
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
798 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
vote
1answer
55 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 ...
-1
votes
1answer
12 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
votes
0answers
22 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
32 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
38 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
113 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
votes
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
vote
1answer
45 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
32 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
925 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
56 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
47 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
votes
0answers
35 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
vote
0answers
29 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
48 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
votes
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
votes
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 ...
1
vote
0answers
26 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 ...
0
votes
0answers
19 views
Procedure for determining the levels of Acrylamide from a cup of coffee
For experimental purposes, I want to determine the level of Acrylamide in cups of coffee. Is there a method that doesn't use spectrometric analysis to determine it as I do not have access to it in the ...
13
votes
3answers
1k views
How is hair tissue mineral analysis performed?
This might be a mixed chemistry / physics question, but I've always wondered what methods were used to precisely determine the levels down to trace amounts of all minerals in human tissues. I know ...
2
votes
1answer
32 views
Evaluate indicator choice (phenolphthalein)
A student wishes to find the concentration of a $\pu{50 mL}$ solution of acetic acid $(K_\mathrm{a} = \pu{1.8e-5}).$ He performs a titration using a solution of $\pu{0.2 M}$ sodium hydroxide. The ...
1
vote
0answers
30 views
Comparing the emission spectrum of ethanol and mixture of alcohols
Sorry if this question has a simple answer, but I've been unable to find it elsewhere.
Using a diffraction grating, burning ethanol (99.9%) will produce a rainbow of colours. However, when burning ...
5
votes
1answer
48 views
How can I figure out if my store bought chlorine is the percentage it says it is?
Chlorine is an important part of maintaining any pool. I've read horror stories of people buying chlorine from pool stores or big box stores and the chlorine being ineffective.
If stored long enough ...
1
vote
0answers
28 views
Acid and base separation on an anion exchange column [closed]
I'm new with this concept and so I would need some advice.
I want to separate an acid and a base in a water solution. The acid has $\mathrm{p}K_\mathrm{a}(\ce{HA}) = 5$ and the corresponding acid of ...
9
votes
2answers
578 views
Testing thermite for chemical properties
I'm writing a movie in which a bunch of military explosive ordnance experts destroy a turbine with thermite and the local fire chief has to work out whether it is plain $\ce{Fe2O3}$ and aluminium ...
3
votes
3answers
54 views
Applying vacuum at the end of a flash chromatography column
I know that flash chromatography uses a positive or pushing pressure to achieve the goal which is separation. Would the same goal be achieved if you had a vacuum on the other end instead of a ...
1
vote
1answer
27 views
What is responsible for the smell of incomplete hydrocarbon burning and what sensor can detect it?
After I pass the smoke from partially burned fuel oil through a filter, I can still very strongly detect the smell. It is the same thing you smell from the exhaust when an old car or truck goes by.
...
11
votes
3answers
679 views
Why are isotopes an issue in reading mass spectra?
It is my understanding that the isotope distribution for carbon and hydrogen, for example, are skewed heavily toward one species, i.e., one isotope accounts for ~99% of the abundance of the element in ...
4
votes
0answers
36 views
What does “at%” mean and how it differs from “mol%”?
Sorry if my question is a bit obvious, but for some reason I'm getting confused with the percentages in this question:
Concentration of $\ce{A}$ is $\pu{80 at\%}$ and concentration of $\ce{B}$ is $...
1
vote
1answer
36 views
Redox titration or iron(II)
The concentration of $\ce{Fe^2+(aq)}$ can be determined by a redox titration using
A. $\ce{KBr}$
B. $\ce{SnCl2}$
C. $\ce{KMnO4}$ (basic)
D. $\ce{KBrO3}$ (acidic)
Can anyone please ...
8
votes
0answers
48 views
Quantitative Transfer of Volatile Standards
(Edited w/ updates) Okay, long story short I work in a lab which has been working on cannabinoid analysis (in the licensed Canadian market) and have had a lot of issues surrounding the standards/...
1
vote
2answers
68 views
How do I convert salinity measured in mg/L Cl into parts per thousand as NaCl?
I have collected water data using a refractometer that records salinity in ‰ (parts per thousand) as $\ce{NaCl}$. I want to compare my data to other data but every journal article I read has the ...
1
vote
0answers
27 views
Measuring pH in ferric oxalate solutions
I have a problem with measuring $\mathrm{pH}$ in ferric oxalate solutions ($\sim 5~\text{to}~\pu{10 g L-1}$ $\ce{Fe},$ $\pu{0.8 M}$ oxalic acid, $\pu{25 °C}$). While I am sure about the $\mathrm{pH}$-...
1
vote
1answer
40 views
In HPLC, how does column diameter affect the retention time?
I am using a smaller diameter column than my previous one keeping all other factors such as stationary phase, solvent, solvent gradient constant. (Obviously, flow rate will be less in smaller column). ...
3
votes
2answers
158 views
Why should AAS use element lamps?
AAS (Atomic Absorption Spectroscopy) is a quantitative analytical technique used to measure very small concentrations of ions in substances. The main idea is that the sample is atomised in a flame and ...
0
votes
1answer
33 views
How to find volume needed from a stock solution
I am making a media that is amended with substrates after being autoclaved in order to keep the media anaerobic. In order to do this, we make stocks of the solutions from a known concentration. I am ...
1
vote
1answer
49 views
Molar absorption coefficient for potassium hydrogen phthalate
I would like to draw a comparison of the sensitivity between several spectrometers. Therefor I measure the absorption of a serial dilution of potassium hydrogen phthalate (KHP). The idea is to compare ...
1
vote
2answers
51 views
Finding molarity of hyposulfite solution used in titration
$\pu{0.1 g}$ of $\ce{KIO3}$ is treated with excess $\ce{KI}$ solution. The liberated iodine required $\pu{44 ml}$ of $x$ molar hypo solution. Calculate the value of $x$.
I have used the equivalent ...
15
votes
1answer
1k views
Using a gas stove instead of Bunsen burner for a flame test?
In all chemistry labs we use the Bunsen burner. What's the difference between it and a good old gas stove used in home? Can the stove also be used to get positive flame tests for some cations (like $\...
0
votes
1answer
55 views
Flame test color for non-ionic compounds
What color would a non-ionic compound, such as $\ce{NH4OH}$ or $\ce{HCl}$, produce in a flame test? Is no color produced, or is it different for each compound?
6
votes
2answers
66 views
Removing sodium borate for the test proving thiocyanate ions
I've just learned that when carrying out the identification test for thiocyanate ions borax can induce a false positive and therefore needs to be removed. I couldn't find the answer on google so I'm ...
