43 votes
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How to differentiate between iron and sodium flames?

Sodium flame is yellow, but all the light is due to two lines in the yellow region. If you look a sodium flame through a purple glass (cobalt glass), the yellow color is absorbed, and you do not see ...
Maurice's user avatar
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30 votes

Is there a commercial liquid with refractive index greater than two?

Taking the definition of refractive index $n = c/v$ into account, $n > 2$ means the velocity of light in the material $v$ is less than half than in vacuum $c,$ so there must be a strong interaction ...
C.X.F.'s user avatar
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27 votes

Why does the weaker C–H bond have a higher wavenumber than the C=O bond?

A property of the harmonic oscillator is that the oscillation frequency, $\omega$, is dependent not only on $k$ (the spring constant) but also on the mass $m$ of the object: $$\omega = \sqrt{\frac{k}{...
orthocresol's user avatar
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18 votes
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How is hair tissue mineral analysis performed?

The analytical technique is called inductively coupled plasma optical emission spectroscopy. It was invented by a chemist V. A. Fassel, although it is pure physics. The specimen is digested in an acid,...
AChem's user avatar
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17 votes
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Is it better to use a smaller, more accurate measuring cylinder several times or a larger, less accurate one for the same volume?

You have three types of errors: The errors in the accuracy of your measurement. Assuming you are reading the water levels consistently (at eye level at the bottom of the meniscus), these should be ...
theorist's user avatar
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17 votes
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Difference between a "cartoon" flame test and a "real" flame test? How do chemists do flame tests correctly?

Your interest is greatly appreciated. As a first step, let's clarify that flame tests as an analytical tool are obsolete. No professional chemist will use them to identify a given unknown sample. ...
AChem's user avatar
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16 votes
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Typesetting of the retardation factor (Rf)

According to Nomenclature for Chromatography (IUPAC Recommendations 1993) [1, pp. 843, 845] (also listed in IUPAC Gold Book), retardation factor is denoted as follows: Column chromatography: $R$ (...
andselisk's user avatar
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16 votes
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Is there a name for this algorithm to calculate the concentration of a mixture of two solutions containing the same solute?

This is a so-called "Pearson's square" or "Box method" of balancing ratios, originally used extensively in dairy industry (at least since 1920s judging from Google Books search). Earlier the similar ...
andselisk's user avatar
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15 votes

Is there a commercial liquid with refractive index greater than two?

To complement @blu_potatos's answer, there are some other contenders having refractive index greater than 2 Arsenic di/trisulfide and sulfur and/or selenium and/or mercuric sulfide in arsenic ...
Nilay Ghosh's user avatar
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15 votes

Conception and manufacture of the Avogadro Project's (nearly) perfect silicon sphere (and, what is “atomic feeling”?)

Short answer: The success of the project benefitted from many contributors. According to BIPM and its Avogadro project, there are two spheres (reference). The page equally refers to a publiction ...
Buttonwood's user avatar
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14 votes
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Remove salt from dirt

Assuming you mean NaCl - the common "salt" (chemists call lots of things salt!). If you extract the salt by physical means, it's a physics question. Assuming that the "dirt" is not (or poorly) ...
Floris's user avatar
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14 votes
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Functional difference of Benedict's solution and Fehling's solution

Fehling's solution consists of two parts, Fehling's A and Fehling's B. Fehling's A consists of aqueous copper(II) sulfate, while Fehling's B consists of aqueous sodium potassium tartrate ($\ce{NaK(...
Pritt says Reinstate Monica's user avatar
14 votes
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pH probe bulb - what is happening within the glass?

My reference for all information and pictures is Harris' Quantitative Chemical Analysis, 9th ed., pp 347-9. I think it'll be worth your while to consult those pages, but I'll try to summarize the ...
a-cyclohexane-molecule's user avatar
14 votes
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How to assign overlapping multiplets in 1H NMR spectra?

Referring to your comment on Buttonwood's answer: Unfortunately, in this case I only have 1D HNMR and IR available to analyse the product If this is really the case, then you are essentially out of ...
orthocresol's user avatar
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13 votes
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Strange batch of potassium nitrate with lower than expected melting point

It might contain $\ce{NaNO3}$ as well as $\ce{KNO3}$. This paper by Foong et. al. cites some thermal measurements, such as melting point and heat capacity, that you could make with a thermometer and ...
DrMoishe Pippik's user avatar
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How does one tell (or conclude) if a substance is carcinogenic?

How do we tell or suspect one compound to be carcinogenic? As written in the comments to the question, this the result of large studies on the human population, correlating blood or urine levels of ...
TAR86's user avatar
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13 votes

Is there a simple way to distinguish grades of purity for copper metal?

It is unlikely that there is a simple method, not involving relatively expensive chemical analysis, for distinguishing 4N, 5N, and 6N copper specimens. Shown below is a photograph of some copper ...
Ed V's user avatar
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13 votes

How to distinguish silver chloride, bromide and iodide?

Nilay Ghosh's method is excellent, but it does not work if the original deposit is a mixture of the three precipitates $\ce{AgCl, AgBr, AgI}$. In this case, it is first necessary to get rid of the ...
Maurice's user avatar
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12 votes

Can phenol be detected with a ceric ammonium nitrate test?

With unsubstituted phenol ($\ce{PhOH}$) dark-brown precipitation is formed: $$\ce{(NH4)2[Ce(NO3)6] + 2 PhOH -> [Ce(NO3)4(PhOH)2] + 2 NH4NO3}$$ Other phenols should produce wine-red solution as ...
andselisk's user avatar
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12 votes

How is hair tissue mineral analysis performed?

Inductively Coupled Plasma (ICP) based techniques are very common for elemental analysis. The goal of such analyses is to quantify the elements present in a sample. The neat thing about this, in my ...
Yoda's user avatar
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12 votes

How to differentiate between iron and sodium flames?

Very good question. I believe you are talking about ordinary Bunsen burner flame which is considered a low temperature flame by atomic standards. Good temperatures for atomic emissions are on the ...
AChem's user avatar
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11 votes
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Why does phosphoric acid mask the colour of iron(III) complex in water?

When phosphoric acid is added to an aqueous solution of iron (III), the ligands in the yellow complexes $\ce{[Fe(OH)(H2O)5]^2+}$ and $\ce{[Fe(OH)2(H2O)4]+}$ ( $\ce{[Fe(H2O)6]^3+}$ are weakly colored ...
Jannis Andreska's user avatar
11 votes
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Why does Devarda's alloy include copper?

Virtually every analytical chemistry textbook's chapter on anion determination mentions that Devarda's alloy is very brittle and can be easily pulverized in a mortar, unlike $\ce{Al}$ and $\ce{Zn}$ ...
andselisk's user avatar
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11 votes
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Does a certain "Badecker reaction" actually exist?

The reaction in question is actually called the Boedeker reaction. How the book came from Boedeker to Badeker I do not know, but maybe there was one instance of Boedeker being written Bödeker which ...
Jan's user avatar
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11 votes
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Why is Prussian blue ‘blue’ in colour?

Prussian blue contains both $\ce{Fe(II)}$ and $\ce{Fe(III)}$. Mixed-valence compounds, such as the one in question, absorb certain wavelengths of visible light resulting due to the phenomenon of inter ...
getafix's user avatar
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11 votes

How does a mercury detector work?

Most commonly they work by pulling air through a UV absorption cell and simply measuring the absorption at 254 nm. Often there is a pre-concentration step involved. This usually involves a gold-...
airhuff's user avatar
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11 votes
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How does a mercury detector work?

There are many ways to detect mercury, and you can find a more detailed analysis of these methods, along with examples of these detectors and their limitations, here. Gold film sensors Gold Film ...
ringo's user avatar
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