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Questions tagged [analytical-chemistry]

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

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Calculating solubility of iron(III) hydroxide in water

The following example in Skoog's Analytical Chemistry uses mass-balance and charge-balance equations to calculate the solubility of iron(III) hydroxide in aqueous solution. $$ \begin{align} \ce{Fe(...
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Choosing the right wavelength for calibration curve and for analysis of actual results

Introduction: I am currently conducting a series of experiments in which I am studying the transport of polystyrene nanoparticles (PNPs) through sand and soil. This is done in sand/soil columns, into ...
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Analysis of a mineral sample containing pyrite [on hold]

A mineral of a process contains $90\%$ $\ce{FeS2}$ and $10\%$ inerts by weight. This material is calcined with $25\%$ excess air according to the reaction: $$\ce{FeS2 + O2 → Fe2O3 + SO2}$$ ...
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Which would be more effective as antifreeze in an automobile? [on hold]

A solution containing: a.) 10 kg of methyl alcohol or 10 kg of ethyl alcohol b.) 10 m solution of methyl alcohol or 10 m solution of ethyl alcohol
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College: Chromatography Analysis of toothpaste. Can someone please review my write up [closed]

[College:Chromatography] Hi there, Im absolutely struggling to know if I done this right or should present everything in a better format! here is the Laboratory manual pg1 pg 2 with the Standard ...
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organic chemistry problems [closed]

how many of nitrogen(N) are present in a 2.0l aliquot of a 3M ca(no3)2 solution? 13mg of vitamin c was detected in a test . 200mg of ground tablets were used in the preparation. if the weight of one ...
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Why do acetate salts turn black on heating?

While performing the dry heating test during the qualitative analysis of white salt, a black residue indicates the presence of Acetate anionic radical. What is the underlying reaction/process behind ...
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117 views

Why is lead(II) present in two groups of cation analysis? [closed]

Well, I found that lead cation $\ce{Pb^2+}$ is present in both group 1 and group 2 of cation analysis. But why?
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Impediments to GC-MS characterization of petroleum products

In an attempt to characterize, and sometimes to 'match' oil on feathers of birds, a laboratory utilize gas chromatographic - mass spectrometry. Persons likely to encounter oiled birds are advise to ...
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What causes the turbidity when preparing Fenton's reagent?

New guy, please be gentle. I might ask questions not according to conventions, I am not a chemist nor do I study chemistry. Feel free to adapt the question and the tagging. I am preparing a solution ...
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Percent hydrogen and carbon [closed]

A 1 g sample of an organic compound was burned in a combustion analyzer and yielded 1.42 g carbon dioxide and 0.872 g of water. Calculate the percent carbon and hydrogen in the sample. From the ...
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When making a calibration curve, do we have to use the wavelength at maximum absorbance?

If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration, does the wavelength have to be exactly at the maximum of the peak? Or can it be somewhere else ...
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The effect of charge density of ligands on spltting of metal ions

this is my first thread! I am currently undergoing a personal investigation that is based on one of the factors which effect the splitting of d orbitals in central metal ion by the charge density of ...
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1answer
41 views

Is Beer-Lambert law also valid for fluorescence and luminescence?

When I measure optical density in a microplate reader the absorbance is proportional to the concentration and the height of the liquid. Is Beer-Lambert law also valid for fluorescence and luminescence?...
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Determining chemical formula of the hydrocarbon via combustion analysis [duplicate]

A container of volume $15\ \mathrm{L}$ contains a hydrocarbon at $27\ ^\circ\mathrm{C}$ and $2\ \mathrm{atm}$ pressure. For the analysis, we take $10\ \mathrm{g}$ of hydrocarbon and the pressure ...
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what is the exact meaning of oxidation state? [duplicate]

can you mention the concept of oxidation state without its simple definition i-e it is the apparent charge +ve or -ve.....😪 I found these in wikipedia but didn't understand."Conceptually, the ...
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1answer
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How does the pH of solutions of salts in which the cation is acidic and anion basic, depend only on the relation of their constants?

My book is not very explanative about it, I'm trying to get the equation: $$[\ce{H^+}]=\sqrt{K_\mathrm{w}\times\frac{K_\mathrm{a}}{K_\mathrm{b}}}$$ but I didn't succeed, can someone explain the ...
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Why is a solution of salt used instead of the salt in test for sulphate ion?

I noticed that in some anion tests like carbonates, the salt is used and in some like sulphate ion the salt solution is used. Why is this so? When do you require a solution of the salt instead of the ...
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1answer
25 views

Acid value of linseed oil

For this we weigh $\pu{1.015 g}$ of linseed oil which is dissolved in alcohol. 3 drops of phenolphthalein (pH indicator) are added and a solution of potassium hydroxide of concentration $C = \pu{9.5e-...
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1answer
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How to accurately determine mass transfer using balances?

I had troubles the other day using a balance that goes to the tenth of a milligram place (i.e. .0005 vs .001 g), when trying to determine how much solid I transferred. I would take some amount of mg, ...
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High content of potassium reported by spectrometer in silverware items

We tried to analyze a few silver items (800/1000 fineness) using a hand-held ED-XRF spectrometer, which is normally used for analyzing industrial alloys etc. The operating element range of the device ...
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59 views

Detecting alkaloids - Dragendorff's reagent

I am writing a book and as part of the plot one of the characters has a plant that contains alkaloids in tincture form. They want to do a test to detect for the alkaloids so they use the Dragendorff's ...
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Bond enthalpy of hydroxide

Why does it require more energy to break the first O-H bond in water than is required to break the second O-H bond?
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Testing for asbestos using readily available chemicals and tools?

Given that it is difficult to determine who is telling the truth in the recent claim that J&J covered up finding asbestos in their powder, is there any chemical test that we can perform on our own ...
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Infrared Spectroscopy of N2O [closed]

Would you be able to identify the stretch and bend in the spectrum? I can not find much information about the $\ce{N2O}$.It's solved, does anyone know the symmetry of these vibrations?
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Determination of molecular formula of hydrocarbons by combustion analysis

So, I've this question in my textbook: $\pu{20 mL}$ of unknown gaseous hydrocarbon reacts with excess oxygen gas. It decreases by $\pu{30 mL}$ upon cooling down. It decreases farther $\pu{40 mL}$ ...
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Is it possible to unambiguously identify a substance with a rapid test?

I've seen a documentary about the narcotics control at the Jorge Chávez International Airport in Peru. The officers used a rapid test to identify cocaine. They put a cotton swab into the substance. ...
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1answer
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How to detect equivalence points? [duplicate]

How do we detect equivalence point from a titration of an acid with a basic titrant from thу titration curve ($\mathrm{pH}$ vs. Volume of titrant added)? Can we predict an equivalence point just by ...
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1answer
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Taking a procedure for ICP and adapting it to use with AAS

I was reading a paper regarding metal detection and they gave their procedure for an acid digest of a soil sample which was then analysed by ICP-OES. They used nitric acid, hydrogen peroxide and ...
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1answer
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Metal Evaporation in GFAAS?

Our lab is doing aqua regia digestion of an ore matrix for the determination of Platinum Group Elements (PGE). We're getting white smoke when we run it through a Graphite Furnace assisted Atomic ...
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1answer
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Identifying food, quick and cheap? [closed]

I’m asking this question in the most technical perspective of identifying substances, so I’m not considering the use of chemical tests like Benedict’s solution, biuret solution, Sudan III stain, or ...
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1answer
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Mole fraction concept

In a certain titration experiment, 1) when $\ce{KIO3}$ solution is added to $\ce{KI}$, the $\ce{I-}$ ion is oxidised to the triiodide complex, $\ce{I3-} $ $\ce{IO3- + 8 I- -> 3 I3- + 3H2O}\tag{1}...
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Will number of moles (amount of substance) of a chemical change when I dissolve it’s solid state in a solvent so it becomes a solution

Let’s say if I have a known mass (10g) of an inorganic compound (NaCl) in its solid form and I dissolve it in water to form an NaCl solution and the total mass of the solution, let’s say 100g. if I ...
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Pressure in Skoog Instrumental Analysis Problem 27-22b (gas chromatography)

Problem 27-22b in: Skoog; Holler; Crouch. Principles of Instrumental Analysis. Thomson Brooks/Cole (publisher varies by country) asks for corrected retention volumes. A compressibility factor, $j$ ...
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1answer
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Conceptual understanding of solution / solute in a question [closed]

6.853g of sodium cyanide was dissolved in water and brought to volume in a 100ml volumetric flask. The final mass of the solution was found to be 107.166g My understanding - A solution is ...
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How do we know cyclopentadienylmolybdenum tricarbonyl occurs as a dimer?

Cyclopentadienylmolybdenum tricarbonyl, $\ce{MoC8H5O3}$, dimerizes to form the cyclopentadienylmolybednum tricarbonyl dimer, $\ce{(MoC8H5O3)2}$. $\hspace{3cm}$ How was it discovered that it does ...
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1answer
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Determination of Urea and Hydrogen Peroxide in Cow Milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy) [closed]

I am doing a research on cow milk adulteration. I am checking Urea and Hydrogen Peroxide content in milk by ATR-FTIR(Attenuated total reflection-Fourier Transform Infrared Spectroscopy). I am using $\...
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What are some example of the use of argentometric titration?

Like, we use alkalimetric titration to calculate the real concentration of table vinegar. What about argentometric titration?
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What happens to chromium (as Cr2O7-) in the plasma of the ICP?

I have recently been analyzing some biological samples for chromium using a standard Cr(VI) solution for external calibration. Cr standards are typically supplied in a 2% nitric acid matrix. That ...
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1answer
54 views

Artificial nose sensors

I'm am doing research in creating an artificial nose. I need to know how this process works by someone with domain expertise; essentially, what technologies are available currently to detect a broader ...
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1answer
28 views

How many samples would be worth when following a desorption? How to relate with limit of detection?

I am following the desorption of a compound from a polymer. Let's imagine that it occurs at a certain rate and most of the compound is desorbed after 5 days (as in the figure). Then, I could use many ...
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1answer
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How do we know that we have isolated a substance?

In The Historical Background of Chemistry by Henry M. Leicester page 131, the author says: Carl Wilhelm Scheele (1742-1786) [...] isolated many organic compounds, including hydrogen cyanide, lactic,...
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1answer
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Dissolving cast iron in nitric acid

Decades ago my job was to find the silicon content in cast iron gravimetrically. The first step was dissolving the sample in hot Nitric acid. Did this turn all of the constituents in the sample, ...
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1answer
32 views

Bromides limit test

I have a question in the monograph of sodium chloride. In the limit test of bromides the limit is 100 ppm but the concentration of the standard is much lower than the limit. So I want to know why. ...
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Isoprene standard preparation dilution Nitrogen

My concern is dealing with Isoprene. I am from a pure electronic background and my research includes dealing with organic vapor. From the literature I came to know that Isoprene commercial form is ...
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1answer
76 views

Normalized standard calibration curve

I have a dynamic assay whose absorbance changes with time. I recorded it’s spectrum initially after preparing it. Then I added my analyte and mixed the contents. Then I waited for 2 min and recorded ...
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3answers
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Why does 2,4 DNP give orange colour crystals?

Why does 2,4 DNP give orange crystals on reacting with solution of aldehydic or ketonic group? Why does this test give orange crystals? Is this related to the electron emissions? This is just a ...
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How to divide the peaks of two anion ions using ion chromatography?

I used an ion chromatography system (Dionex IC-2000) to determine the inorganic ions and acid from the samples collected in the atmosphere. For measuring $\ce{SO4^2-, NO3, Cl-}$, and low molecular ...
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What is the proof of complete ionic dissociation in water?

Is there any way to prove that ionic compounds, for instance $\ce{NaCl}$, completely dissociate into singular $\ce{Na+}$ and $\ce{Cl-}$ ions within water by hard experimental evidence? Besides ...
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2answers
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Does ICP-OES detect molecules in suspension?

I'm curious whether ICP-OES has the ability to detect molecules in suspension?