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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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What methods are used to detect a particular molecule? [on hold]

What methods are used to detect a particular molecule? I know of raman spectroscopy and "test" reactions (forming coordination complexes, iodine starch test, silver mirror test etc.)
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Would two different Plaster of Paris samples have different chemical signatures?

Weird question, but... would a spectroscopic analysis of a plaster of Paris sample reveal a chemical identifier that could be used to compare that sample against another. I want to be able to say ...
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1answer
45 views

What defines a proton as “labile” in NMR? [on hold]

What makes some protons labile and others not? For example the OH and NH2 protons get exchanged but CH ones don't. When we use the D2O test, we say the labile protons get exchanged for D so their ...
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How can I evaluate the molar mass of the cation or anion in a solid substance from its molar mass? [on hold]

I can't evaluate the molar mass of a cation or anion from a given molar mass of a solid substance. Like $\ce {Ni(DMG)2}$ has the molar mass $\pu{288.69 g/mol}$ and in my book there is given that in $\...
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Determination of pKa and molar absorptivity coefficient using spectrophotometry [on hold]

An indicator BPB (Brophenol Blue) is used and dissolved in solutions of various known $\mathrm{pH}$. Then, the absorbance of each solution at 590 nm was measured and the question asks for molar ...
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1answer
25 views

Diluting a sample of weak base before titration. What happens to equivalence point pH of diluted vs undiluted?

A student titrated a 10.00 mL of 0.20 M methylamine ($\ce{CH3NH2}$) and determined that 10.00 mL of $\ce{HCl}$ was needed to reach the equivalence point. If you diluted your original sample of ...
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1answer
35 views

IUPAC Recommendations for Concentration Units (ppb, ppm)

In a recent interesting post, (Is 1 ppb equal to 1 μg/kg?) it was pointed out that IUPAC advises to abandon parts per million, parts per billion quantities and instead it suggests to employ micromole/ ...
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22 views

About the percentage yield and purity

I was wondering why all of the percentages like mass percent composition, percentage yield and percentage purity are calculated using masses. Wouldn't it make more sense to use number of moles of the ...
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2answers
28 views

Sodium Sulfate vs Sodium Sulfite

I recently took a test and one of the questions was: Which procedures will allow a student to differentiate between solid sodium sulfate and solid sodium sulfite? I. Make solutions of each ...
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1answer
21 views

Analyzing composition of a sample in terms on elements

I've a sample and I need to know the chemical composition in terms of its elements. I'm not a chemist, I dont have monies to buy instruments. What are my options? I like DIY stuff. I'm not very ...
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2answers
65 views

In Lassaigne's test, the organic compound is first fused with Sodium Metal instead of any other Group 1 Metal, Why is this so?

I know that Sodium has high polarising power than potassium so it can convert the respective functional groups more readily than Potassium and both Lithium and Sodium salts are soluble in water. This ...
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How can I determine the sulfuric and phosphoric acid content of a solution by titration with NaOH? [duplicate]

I have been tasked with determining the quantities of sulfuric acid and phosphoric acid in a solution via titration with 1 N NaOH. I am using Methyl Orange and Phenol Phthalein indicators for the ...
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1answer
122 views

Percent Dissociated from Titration Curve

Question 818 references the titration curve. Answer is A because $\ce{H+}$ conc $= 10^{-4}$. This is conc of dissociated acid. The conc of the undissociated acid is the original concentration minus ...
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Chemical test to identify and differentiate keratin from chitin

If I have a filament of unknown biological origin, what chemical test can be used to determine if it is chitin or keratin? Can this be done in the average university chem lab?
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2answers
41 views

Calculating the pH of a buffer made by a diprotic acid and its double salt

The concentration of the diprotic acid (tartaric acid) will be constant at $\pu{ 0.1 M}$. I want to find the concentration of its double salt (potassium sodium tartrate) needed to create a buffer of $\...
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1answer
32 views

Simple tests for presence of CO₂

Am aware that one method for testing for the presence of $\ce{CO2}$ is passing the gas through limewater, with it going cloudy if positive. Are there any other convenient methods?
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2answers
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Equilibrium constant for esterification process

Teacher told us that the concentration term for pure liquids and solids is always $1$. But online I found this reaction: $$\ce{CH3COOH(l) + CH3CH2OH(l) <=> CH3COOCH2CH3(l) + H2O(l)}$$ ...
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1answer
36 views

How Can I Test Something for the Presence of Iodine? [duplicate]

I want to test a supplement for the presence of iodine. Iodine should turn starch blue-black. So, can I powderize the supplement tablet, add water to it, drop it on a piece of bread, and if it turns ...
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0answers
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What is the formula for theoretical buffer capacity for a diprotic buffer system?

According to Chembuddy, the formula for theoretical buffer capacity for a monoprotic buffer system is as follows: where Cbuf is the total concentration of buffer and Kw is the water ionization ...
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1answer
42 views

Why is maximum buffer capacity for some diprotic buffers not when pH = pKa?

According to Rajkovic et al. [1]: $$β = \frac{[\ce{H+}]}{K_\mathrm{w}} + 2.303\cdot\frac{[\ce{H+}]\cdot K_\mathrm{a}\cdot c}{[\ce{H+}] + K_\mathrm{a}}$$ where $K_\mathrm{a}$ is the ...
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2answers
173 views

Is oxalic acid dihydrate considered a primary acid standard in analytical chemistry?

Using oxalic acid dihydrate as a primary standard just seems really odd to me. I'd expect a primary standard to be oven dried. It just seems weird that a hydrate would be used. Granted, I saw ...
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1answer
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What is wrong with storing deionized water in glass containers?

I have heard that in general storing deionized water in glass bottles is ill advised and that it is better to use plastic. Additionally this is especially important for water used in ICP. I have ...
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1answer
41 views

Effects of Ka on the Half-Equivalence Point

I'm new to studying chemistry at a university level and am currently reviewing acid-base titrations. I am wondering about the relationship between your ionization constant for a weak acid ($K_\mathrm{...
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1answer
23 views

Flame Ionization Detector versus Mass Spectrometer

Why is chromatographic separation more important with a flame ionization detector than with a mass spectrometer?
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1answer
554 views

Is there a name for this algorithm to calculate the concentration of a mixture of two solutions containing the same solute?

There is an algorithm called "Mischungskreuz" (German for "x of mixing") that is sometimes taught as a shortcut to figure out the following problem: You have two solutions that contain a solute at ...
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2answers
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In Ion Chromatography instrument, Does the specific conductivity (peak area) of an analyte depends upon background conductivity?

In Ion Chromatography instrument, Does the specific conductivity (peak area) of an analyte depends upon background conductivity ? Assume Specific Conductivity (peak area) of fluoride ion is 4 unit ...
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1answer
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How to determine the number of water ligands attached to Pd in palladium chloride aquacomplex PdClₓ · yH₂O?

Normally this can be achieved using UV-vis: there is a strong absorbance around wavelength 220 nm which varies based on the number of ligands. If the palladium concentration is too high, the solution ...
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1answer
30 views

log K vs Internal Energy Question

In a photonionization experiment the neutral molecule absorbed three 266 nm photos. If the kinetic energy of the electron removed during ionization is 1.4 eV, what is the ratio of the simple cleavage ...
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2answers
33 views

How to report result to the nearest 0.01 mg/L?

what is meant by reporting result to the nearest 0.01 mg/L? The test result in certificate show 7 mg/L showing no decimal point.
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1answer
31 views

Defining sensitivity of TOF Mass Spec - Does the detector play a role?

Looking at TOF MS systems, my current understanding is that temporal resolution results in mass resolution - so by controlling the flight time (with distance) and sampling rate, you can start to ...
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0answers
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Is the analyte included in the ionic strength equation?

I don't quite understand the calculation for ionic strength of a solution. The formula includes the concentration and charges of the ions in solution, however, is the analyte (whatever we're trying to ...
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Qualitative analysis of iron(III) salt

Why will $\ce{Fe^3+}$ give brown ring test? In my textbook it was given that ferric ion gives brown ring too. I am confused, if ferric ion is already present, then what will reduce nitrate ion to ...
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1answer
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Is it more precise to measure a substance as a solid or as a liquid?

If I have a substance and want to obtain an exact quantity of it, is it better to measure it as a solid or as a liquid? In other words, if I have, for example, NaCl crystals I can weigh the crystals ...
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2answers
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Should the tip of the burette of an automatic titrator be immersed in the analyte?

In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't ...
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1answer
37 views

Measure the concentration of lactose in dairy products [closed]

I would like to measure the concentration of lactose in various dairy products : milk, cheese, yoghourt... How is it done in labs ? How can I do that using cheap equipments ? Thanks
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1answer
70 views

Distribution coeffecient without concentrations

From what I understand about distribution coefficient is straight from my book — which does not give any practice examples — is that $$D = \frac{C_\mathrm{A}(\text{ext})}{C_\mathrm{A}(\text{orig})}$$ ...
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1answer
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Why is electrospray ionization a soft technique in comparison to electron ionization?

I know that electrospray ionization (ESI) is a soft ionization technique and that electron ionization (EI) is not, because it causes a great amount of fragments in a fast time due to the fact that a ...
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1answer
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How to measure concentration of arsenite and arsenate in a water sample

A colleague and I are developing a transgenic bacterial strain that contains an arsenite oxidase gene. The bacteria can oxidize arsenite into arsenate autotrophically. We need a method to measure the ...
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2answers
257 views

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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1answer
169 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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2answers
55 views

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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2answers
65 views

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
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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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2answers
39 views

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
98 views

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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0answers
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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 ...