Questions tagged [analytical-chemistry]

The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.

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How is 1 mole hypochlorite ion equivalent to 1 mole chlorine gas?

According to my book, 1 mole ClO- is equivalent to 1 mole Cl2. How is that even possible? 1 mole ClO- contains 1 mole Cl atoms. On the contrary, 1 mole Cl2 gas contains 2 mole Cl atoms. So, how are ...
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Should I write formula for oxalate or oxalic acid while balancing a redox reaction using the ion-electron method?

Problem: Balance the following reaction using the ion-electron method: $$\ce{H2C2O4 + KMnO4 + H2SO4 -> CO2 + MnSO4 + K2SO4 + H2O}$$ My book's solution: Oxidation half-reaction: $$\ce{C2O4^2- -> ...
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Why did my book write S2- if hydrogen sulfide isn't ionic?

Problem: Balance the following reaction using the ion-electron method: $$\ce{KMnO4 + H2SO4 + H2S -> MnSO4 + S + K2SO4 +H2O}$$ My book's solution: Oxidation half-reaction: $$\ce{S^{2-}->S + 2e^{-}...
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Thiourea assay determination [closed]

My Name is Nazanin and I am working in a pharmaceutical company. I am trying to determine Thiourea assay. During the experiment I use 0.01 M ferric ammonium sulphate as an indicator. According to the ...
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Convention for writing concentration units

1st part of my question: Q) The concentration of an NaCl solution is 1M. Express this in percent wt. by vol. unit. Ans: $$\text{In %(w/v) unit}=\frac{58.5\pu g}{1000\pu{mL}}\times \frac{100}{100}=5.85\...
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Why is carbonyl peak seen at 1612 cm-1 why is the peak seen so low

the ketone is next to a phenyl ring and the only peak that is within range is 1612 cm-1 why is it so low
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Titration using OTC washing soda (sodium carbonate.) should I use 105.9888 g/mol (anhydrous) or 286.1416 g/mol (decahydrate)?

Looking to make up a little toy/non serious titration to approximately measure the concentration of household acids using sodium carbonate as my standard solution. Doing a quick internet search ...
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Ion Exchange chromatography [closed]

Suppose that Anion exchanger is used in the stationary phase normally -ve charge A.A will be eluted first as it will not attach but my question is does the zwitter ion(have net charge 0 will be the ...
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Performing the mean and standard deviation for a extraction based on averaged content determination

Is it okay to perform the mean and standard deviation for a triplicate extraction based on averaged values of content determination? I performed an extraction in triplicate. Each one of the ...
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Can I expect the same (or very close) peak areas from herbal extracts prepared with the same plant/solvent ratio?

I prepared an extract by using 100 mg of plant and 2 mL of ethanol, filtered and injected 20 μl into the HPLC system equipped with Waters® XSelect (150 mm × 4.6 mm, 5 μm) column. If I prepare an ...
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Which indicator to use for a titration with end point of 2.95 ph?

Metacresol purple and Thymol blue are the closest I was able to figure out but they change at 2.8 ph. Is that good enough or should I use something else?
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Determining iron(III) content in mixture of iron(II) and iron(III) [closed]

Problem Outline a plan of an experiment to determine the percentage of iron present as iron(III) in a solution containing $\ce{Fe^3+(aq)}$ and $\ce{Fe^2+(aq)}$ ions. You are provided with zinc, a ...
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Do both phosphoric acid and sulphuric acid prevent oxidation of ferrous ion in iron titration?

For the Determination of iron by Redox Titration experiment, I am finding the role of sulphuric acid and phosphoric acid. Then I found that other than $\ce{H3PO4}$ masks the yellow color of $\ce{Fe^3+}...
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How might one distinguish between two acyclic diastereomers other than by X-ray diffraction?

I have a mixture of two racemic diastereomers (R,R and R,S - and their enantiomers), and while I can fairly easily tell with 2D spectra which NMR signals correspond to one molecule and which signals ...
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How can I get a breakdown of different salt contents in a fertilizer solution?

I am experimenting a lot with hydroponics i.e. growing plants in a liquid solution. From time to time, I would like to do a check on what is the current salt level for major salts (ions) in parts per ...
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Fractional Composition of Acid Question

I present to you a fractional composition question that my professor refuses to answer because he encourages me to use equations without understanding them. Any help you can provide would be very, ...
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1 answer
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Why can I extract all metabolites from blood plasma with one solvent, but to extract only fatty acids I must use many solvents?

I want to do a metabolite study using GC- without derivatization and UPLC-MS (RP and NP) on samples of plasma and urine. My hypothesis is agnostic about which metabolite will correlate with the ...
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1 answer
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Why don't universal indicator solutions react with themselves?

Universal indicator is a pH indicator made of a solution of water, 1-propanol, phenolphthalein, sodium hydroxide, methyl red, bromothymol blue, sodium bisulfite, and thymol blue that exhibits ...
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Mass spectra interpretation for monitoring Buchwald–Hartwig coupling

I am conducting a synthesis involving Buchwald-Hartwig coupling. The starting materials are 2,3,5-tribromothiophene (MW=320.83) and 1-aza-18-crown-6 (MW=263.33). I used $\ce{Pd_2(dba)_3}$ (MW=915.7) ...
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For Radiochemistry why is a recovery range of 30-110% acceptable for isotopic tracers used for alpha spectrometry analysis of radionuclides?

Just like the title says. I am right now isolating and concentrating several radionuclides from environmental samples using micro-coprecipitation to be able to analyze it on an a alpha spectrometer. ...
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1 vote
1 answer
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How to find out amount of carbon in metal

I am an student of archaeology and on my final work I am working with mining hammers, on which metallography was used. But my supervisor want to use some kind of acid on the surface of the metal so it ...
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1 answer
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Determination of chloride content in aluminium chloride by titration

TLDR: Is there an as simple and direct as possible method to measure chloride content by titration? I want to measure the content (mass fraction) of chloride in $\mathrm{AlCl_3}$ powder by titration. ...
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Calculation of hypochlorite concentration from active chlorine

So in the lab we got sodium hypochlorite solution. The concentration is in active chlorine (13%) on the label. How do I calculate it to concentration of hypochlorite? I need certain amount of ...
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4 votes
1 answer
135 views

Molar conductivity calculation in a titration curve

At an exam for analytical chemistry, I was asked to calculate the molar conductivity of a solution for an ongoing titration. I just solved it the way our professor showed it to us but I have some ...
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chromatographic interactions with methanol, acidic or basic?

How can I describe the interaction between methanol and thiophene in a chromatographic separation in an acid media? I'm confused with the different concepts: Methanol present a hydrogen acceptor ...
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2 votes
2 answers
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Reaction kinetics of exothermic reaction

A colleague said we can’t dissolve a salt (whose solvation enthalpy is exothermic) faster if we increase the temperature (the solubility equilibrium product is not reached) because Le Chatelier‘s ...
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6 votes
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Are double spike isotopic standards suitable for quantification by isotope dilution mass spectrometry?

I would like to apply isotope dilution mass spectrometry (IDMS)* to quantify lead at trace levels. A good spike solution for the process would be the NIST SRM 991 which is an enriched material of ...
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Why the electrode that is the electron source on a x-ray tube is called cathode? [closed]

In electrochemistry, the electrode that lose electrons and oxidizes is called anode. Why on an x-ray tube the electrode that lose electrons is called cathode?
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1 answer
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An Index Poisoning Case Involving Dichlor and Carbonic Acid [closed]

I'm currently working an unusual case of poisoning, with Sodium Dichloro-S-Triazinetrione. In my case, I need to know the expected reaction with carbonic acid. I'm also curious if anyone could give ...
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Wave Dispersive X-ray Fluoresence and Bragg's Law

Thermo Fisher website explains that "WDXRF uses crystals to disperse the fluorescence spectrum into individual wavelengths of each element, providing high resolution and low background spectra ...
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How would I find what specific wavelength I need to measure for a specific chemical in spectrophotometry (calcium perchlorate)?

I am currently doing a research project, and for it, I would like to use a photospectrometer to find the concentration of Calcium Perchlorate in my sample solutions. My current method of data ...
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Applied potential to Saturated silver electrode

I recently did my first cyclic voltammetry. I used a saturated silver reference electrode and two platinum working and counter electrode. This was done with an IKA electrasyn 2.0 device, my parameters ...
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3 votes
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How to adjust selectivity of gas-permeable PDMS membranes for environmental applications?

I have an idea about making an environmental sensor that uses a gas-permeable membrane (GMP) and how its probe could be submerged in a water source with an off the shelf gas sensor. So far, my ...
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0 answers
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Testing for lead in alcohol

I want to test for lead in alcohol rather than water. The reason for this is that I have many antique crystal decanters and flasks. Crystal is made with lead oxide (PbO) added to the glass. Normally ...
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Precipitation of equimolar amounts of chloride and bromide [duplicate]

I was just wondering about the following situation; if we had a solution containing 0.1M bromide and 0.1M chloride ions, and treated it with excess silver nitrate, what would happen and would ...
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2 votes
0 answers
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Chemical analysis of campholene nitrile

I have a problem. I am synthesizing an organic compound called campholene nitrile (2,2,3-trimethylcyclopent-3-en-1-ylacetonitrile). I need to analyze it. But there's a problem. I do not work for a ...
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1 vote
1 answer
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Optimal lipophilic solvent for washing PEEK-lined reversed-phase HPLC columns

What would be the reasonable strategy for washing a reversed-phase (RP) octadecylsilyl (ODS) C18 HPLC columns from lipids and other non-polar residues? The columns are used for biochemical analysis of ...
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5 votes
1 answer
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The relationship of the osmotic pressure of a polymeric solution and its the molecular mass

Why is the osmotic pressure of a polymeric solution decreases when the molecular mass is increasing? I am honestly unsure if the above statement is true, at least it seems to me to be true. When I ...
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1 vote
1 answer
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What is the function of thin layer in thin layer chromatography?

I just learned about the thin layer chromatography, which I think is basically the same as the paper chromatography. I am wondering what is the function of the thin layer? I mean, what's special about ...
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1 answer
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Finding the percent of light absorbed by a sample [closed]

I have an absorbance of $0.266$ and need to find the percent of light absorbed by the sample. Is it found by just turning it back into transmittence% and subtracting 1? So by that, would it be $(1 - 0....
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2 votes
0 answers
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Why do the splitting pattern on my NMR differ from those stated in literature?

I attempt the synthesis of p-toluic acid using the Grignard reagent (prepared from 4-bromotoluene and Mg) and dry ice. The NMR of the raw product was recorded using $\ce{CDCl3}$ and a peak showing ...
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-1 votes
1 answer
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Why in calculating 25 mM of Tris HCl the answer in gram is automatically refer to the gram in 1000 ml [closed]

In the lab class,my teacher told me that the answer i get in grams is automatically the grams in 1000 ml. Why is it possible without we doing anything the grams i get automatically the grams in 1000 ...
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1 vote
1 answer
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Understanding weak acid-strong base titration

Today I stumbled across a website which defined the titration of weak acid and strong base as the following: "The titration of a weak acid with a strong base involves the direct transfer of ...
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1 vote
1 answer
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How Does Differential Scanning Calorimetry (DSC) Differentiate Between Exothermic and Endothermic Changes?

In DSC, heat flux difference between sample and reference is measured as function of temperature while temperature of sample and reference are maintained the same. DSC is often used for polymer ...
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10 votes
3 answers
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What is the English translation of the German term "Aufschluss", a method to get insoluble analytes into solution?

In the analysis of solids, often the first step is to get the analyte into solution in some form. Sometimes, solids are heated in the presence of acids (acid digestion) or molten salts (sample ...
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1 answer
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Displacement of salts due to higher solubility

I was wondering why mixtures of salts in the same solution precipitate excactly in order of their solubilities. Imagine a solution with NaCl, NaBr, NaI in equal moles. If AgNO₃ solution is now added ...
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1 answer
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Approximation for pH calculation with diluted acids in weak-strong titration curve

I was wondering how one could calculate small pH changes in titrations with dilute acids. As we know, usually we approximate the pH by saying that the conversion is quantitative. For example, when we ...
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0 votes
1 answer
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How do I quantify a mix of SiO2 (amorphous), silicon (amorphous, polycrystal), graphite (dust) in a solid sample?

I collected solid samples from a plugged tube-side of a heat exchanger. These deposits include compounds such as hexachlorodisilane, hexachlorodisiloxane, pentachlorodisilane, graphite dust and ...
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2 votes
2 answers
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Elucidating an unknown compound using 1H- and 13C-NMR spectral data [closed]

I am currently struggling with the following NMR spectrum for this compound: I know for sure that we should multiply the integrals of the hydrogen atoms by four, and that the compound contains at ...
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3 votes
1 answer
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Is absorbance from HPLC UV detector comparable between runs?

Suppose that I have an HPLC with a variable wavelength UV detector, as well as two pure protein samples that differ by a point mutation (otherwise same concentration, extinction coefficient, buffer ...
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