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Questions tagged [elemental-analysis]

The science of determining the elements a compound is made of or deriving the sum formula thereof. Can be applied both to practical and theoretical questions

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16 votes
3 answers
2k views

How can I identify the material of this mystery gear?

I have this small gear which has sat on my desk for a couple years. I can't remember where it originally came from or what material it's made out of, so I'm hoping you can help me solve this mystery. ...
hifkanotiks's user avatar
15 votes
1 answer
2k views

Why do rare earth metal oxides vary in color so much?

I only know a little about what causes different color, but I know it has to do with the electron orbitals and how they reflect or absorb/emit incoming light. The rare earth metals are in the ...
Ryan's user avatar
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13 votes
3 answers
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 ...
Veritas's user avatar
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9 votes
2 answers
1k views

How does a mercury detector work?

I am new to chemistry and saw a "portable mercury vapor monitor." How do these machines work?
user40071's user avatar
9 votes
2 answers
1k views

Why are sulfites often ignored in soil studies?

From a document on soil chemistry that I am reading: The acid-base potential of a soil takes soil pH, total sulfur (sulfides and sulfates), and neutralization potential into account to determine the ...
Al Lelopath's user avatar
9 votes
1 answer
40k views

How to find the molecular formula for a hydrocarbon compound from known combustion products?

What is the molecular formula of a compound containing only carbon and hydrogen if combustion of $1.05~\mathrm{g}$ of the compound produces $3.30~\mathrm{g}~\ce{CO2}$ and $1.35~\mathrm{g}~\ce{H2O}$ ...
shaima's user avatar
  • 107
7 votes
2 answers
177 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 ...
bobsburger's user avatar
7 votes
1 answer
443 views

Determining stoichiometry in ICP-OES data analysis

I have questions regarding data analysis for an inductively coupled plasma (ICP) experiment from a paper by Wang et al. [1]. The generic formula for the chemical compound is $\ce{Na_{2−x}Fe[Fe(CN)6]}$...
Alvero's user avatar
  • 93
6 votes
1 answer
868 views

Representing woody biomass concentration for kinetic reactions

Woody biomass is composed of cellulose, hemicellulose, and lignin components. The following diagram provides representative formulas for each component: Biomass can be represented by it's density, ...
wigging's user avatar
  • 299
6 votes
1 answer
2k views

Why is copper (II) oxide used in quantitative analysis of carbon?

What is the significance of using cupric oxide in the quantitative analysis of carbon? As far as I can tell from my research, only $\ce{CuO}$ is used to oxidize carbon to $\ce{CO2}$. Why can't we ...
JM97's user avatar
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5 votes
2 answers
866 views

False positive test for chloride ions during lab practical

In my highschool practical examination yesterday, I was given an inorganic salt to identify using chemical tests. The test I performed for the presence of chloride was to heat salt in a test tube with ...
Gaurav Sai Maddipati's user avatar
5 votes
1 answer
1k views

Can we use silver nitrate to distinguish between chloride and carbonate salts?

Initially, we are given a solution containing two salts, they can be either carbonate or chloride salts (we do not know their composition initially). Generally, $\ce{AgNO3}$ is used as a confirmatory ...
Jay's user avatar
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5 votes
1 answer
103 views

Can chemicals be identified by their molar mass?

Wouldn't it be possible to identify a chemical by measuring its molar mass? How much accuracy does the measured molar mass need to be to guess what chemical it could be? EDIT: @ortho makes an ...
TanMath's user avatar
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4 votes
2 answers
4k views

Method and Tips for Inorganic Qualitative Analysis

In a few weeks time, I will be doing an inorganic qualitative analysis test which is very pressed for time (a majority of people don't finish). The form of the test is most likely going to be that ...
Nanoputian's user avatar
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4 votes
1 answer
2k views

index of hydrogen deficiency

I don't really get the concept of index of hydrogen deficiency (IHD). Can someone please use an example to explain what $\mathrm{H_{reference}}$ and $\mathrm{H_{molecule}}$ are? I know the formula: $$...
Unistudent9's user avatar
4 votes
1 answer
357 views

In TOF Mass Spectrometry how does the detector 'know' the difference between ions of different elements?

After the positive ions have been accelerated, I know that they travel through the drift zone at different speeds due to their masses. But surely, a heavier ion/element that enters the drift zone ...
Ben Hughes's user avatar
4 votes
1 answer
191 views

XPS analysis intrepretation

A lab presented me with an elemental composition (mainly metals in char) derived from an XPS analyzer and mentioned that binding energies suggested a list of compounds (various oxides, sulfides and ...
user110084's user avatar
4 votes
1 answer
2k views

Carius method for quantitative analysis of halogens

Carius method: A known mass of an organic compound is heated with fuming nitric acid in the presence of silver nitrate contained in a hard glass tube known as Carius tube, (Fig.12.17) in a furnace I ...
user avatar
3 votes
4 answers
3k views

Chemical elements or compounds with yellowish white color [closed]

Are there chemical elements or compounds that have a yellowish white (cream) color in their natural state?
Somanna's user avatar
  • 213
3 votes
1 answer
396 views

Organic molecules with 21.62% oxygen

I have been told to answer the following question: Seven different compounds, all either alcohols or ethers, contained 21.62% oxygen. Find the structural formula for all of these compounds and ...
Maxim Vaughan's user avatar
3 votes
2 answers
397 views

How to determine the molecular formula based on molecular weight, amount of substance, and partial masses of some, but not all contained elements?

I am working on a chemistry assignment and can’t figure out part of the problem. $\pu{0.2 mol}$ of a compound with a molecular weight of $82$ contain $\pu{9.6 g}$ of carbon, $\pu{1.2 g}$ of hydrogen ...
Mark's user avatar
  • 312
3 votes
2 answers
230 views

Does ICP-OES detect molecules in suspension?

I'm curious whether ICP-OES has the ability to detect molecules in suspension?
Tunk's user avatar
  • 315
3 votes
1 answer
1k views

How can I check if this mystery compound is strontium bromide?

Trying to identify a mystery compound, here are some of my notes, I'm trying to get a second opinion on what it might be! Observations Appears as a white powder, some chunks are formed, sticking to ...
23k's user avatar
  • 133
3 votes
1 answer
63 views

Why is there a [M-1]+ in lieu of a parent signal in the Mass Spectrometry of Primary Alcohol Chains?

I have looked virtually everywhere for an explanation of why alcohols EI GC-MS always have a more prominent M-1 signal over a Parent chain signal--sometimes no parent signal at all. One site says http:...
James Perrin's user avatar
3 votes
1 answer
276 views

Detection of Nitrogen and Sulfur in Lassaigne's Test

In Lassaigne's test for the detection of nitrogen and/or sulfur in organic compounds, we prepare Lassaigne's extract. In this extract, NaCN is formed if nitrogen is present, and $\ce{Na2S}$ is formed ...
R H's user avatar
  • 39
3 votes
1 answer
392 views

How to measure the amount of calcium in a supplement?

In chemistry lab, my group was assigned to determine the actual amount of calcium in a supplement. We did this successfully using HCl to dissolve the tablet, vacuum filtration, and then the addition ...
Gotthold's user avatar
  • 133
3 votes
0 answers
201 views

What causes HPLC peaks to look like gauss curves?

I was wondering how the form and curvature of HPLC peaks come to be. As I understand it, the mobile phase which contains the analyte, runs through the column. Many times, the distribution equilibrium ...
Mäßige's user avatar
  • 265
3 votes
0 answers
477 views

Why aren't lasers used as light sources for atomic absorption spectroscopy?

Atomic absorption spectroscopy yields extremely narrow signals. It is difficult to separate white light with sufficient precision using monochromators, and hollow cathode lamps are often used as light ...
Martin's user avatar
  • 731
3 votes
0 answers
2k views

Lassaigne's test for sulfur

The sodium fusion extract is acidified with acetic acid and lead acetate is added to it. A black precipitate of lead sulphide indicates the presence of sulphur. What is the need for acidification of ...
JM97's user avatar
  • 3,477
2 votes
1 answer
29k views

Elements of paper

I learnt that everything is made up of atoms even paper! After that, I was thinking what are the elements that made paper? Is there any chemical symbol for paper in general?
Simon-Nail-It's user avatar
2 votes
3 answers
129 views

How to identify salts using mutual reactions

There are ten test tubes in the rack at your disposal (1 – 10) and each test tube contains one of the aqueous solutions of the following salts: $\ce{Na2SO4, AgNO3, KI, Ba(OH)2, NH4Cl, Ag2SO4, Pb(NO3)2,...
Harikrishnan M's user avatar
2 votes
1 answer
2k views

Calculation of empirical formula from elemental analysis

A compound contains 40.0% Carbon, 6.7% Hydrogen, and 53.3% Nitrogen (by mass). Calculate the empirical formula. I'm getting $\ce{C7H14N8}$, but my professor says it is $\ce{CH2N}$. Which is the ...
Matt's user avatar
  • 31
2 votes
2 answers
3k views

experimentally determine oxidation state of Iron compound

I need to make several Iron compounds but I am having a bit of trouble finding a decent way to determine the oxidation state of Iron. I'm starting with a Iron(II) compound that I try to oxidize using ...
Arno van der Weijden's user avatar
2 votes
1 answer
50 views

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 ...
Wednesday Fades's user avatar
2 votes
1 answer
830 views

Heating organic compound in a stream of nitrogen gas

This is related to estimation of percentage of oxygen in an organic compound and my textbook states: A definite mass of an organic compound is decomposed by heating in a stream of nitrogen gas. I ...
JM97's user avatar
  • 3,477
2 votes
1 answer
15k views

Detection of potassium ions

I've bought a white powder. The label on the package states that the powder contains sodium chloride, potassium chloride and potassium citrate. How can I make sure that the powder does indeed contain ...
Andrey Sboev's user avatar
2 votes
1 answer
142 views

Equipment recommendation for atomic absorption spectroscopy (AAS) testing for mercury, lead, and cadmium

I work in a public health laboratory in a small mining town and we have the chance to buy equipment to test for lead and cadmium in wastewater, and mercury in not just wastewater, but also in blood, ...
JPertuz's user avatar
  • 29
2 votes
1 answer
1k views

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, ...
Bob's user avatar
  • 21
2 votes
1 answer
252 views

Reagents used to prepare organic ICP standards, from scratch

I am trying to figure our how I can make my own calibration standards for organic ICP analysis. I assume that I need organometallic compounds to mix with base-oil/mineral-oil to prep the standards, ...
Ochemwiz's user avatar
2 votes
1 answer
251 views

Determine the quantitative composition of a solid sample containing Co, Mn, Al, C, and O

I have a solid sample that contains Co, Mn, Al, C, and O. The sample mass is ~200 mg. I need to determine what the composition of this sample is. I've looked at atomic adsorption spectroscopy, but ...
Jon R's user avatar
  • 344
2 votes
0 answers
52 views

Negative absorption coefficient

What does a negative absorption coefficient mean? In detail - I participated in a Synchrotron virtual laboratory. I have to analyze the results and understand what a negative absorption coefficient ...
Roni Amit's user avatar
2 votes
0 answers
74 views

Prepration of standards for analysis of chromium using AAS

I have conducted experiments to study specific adsorption of chromium in various soils and I made my all solutions of cr with using 0.01M NaNO3 as background electrolyte. (I made solutions of 5 ...
DILEEP SINGH's user avatar
2 votes
0 answers
48 views

Preparation of isotopic CO2 standards from Sn-encapsulated CaCO3

I wish to prepare isotopic CO2 gas standards for highly 13C enriched CO2. The CO2 concentrations will be ~1000 ppm, with the balance either N2 or zero air. My plan is as follows: Encapsulate labeled ...
user278411's user avatar
2 votes
0 answers
194 views

Which salts give the sodium carbonate bead test?

Apart from the borax and the phosphate bead tests, there's also this one. It's done by heating the white bead of sodium carbonate and the salt with potassium nitrate; green and yellow colours ...
harry's user avatar
  • 1,134
2 votes
0 answers
86 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?
wav scientist's user avatar
2 votes
0 answers
87 views

Quantitative elemental analysis in mixtures with internal standard normalization

I am trying to make a quantitative model for Laser Induced Breakdown Spectroscopy (LIBS) analyzing metal alloy samples. I am using an internal standard normalization (so far it produced the best ...
udushu's user avatar
  • 121
2 votes
1 answer
69 views

Free refined value in Rietveld

I have a question about Rietveld refinement The author of this paper claimed that the free refined CN ligand is 1.081. However, they does not show how they got that number. They stated it was based ...
Alvero's user avatar
  • 93
1 vote
3 answers
180 views

Combustion analysis methodology question

I am questioning the answer key of an exam question my chemistry professor has given, because I think there is a flaw in the methodology of the exam answer. I have worked out my solution using my ...
Liam White McShane's user avatar
1 vote
4 answers
924 views

Does a grain of salt have exactly equal amount of sodium and chlorine?

Does a grain of salt have exactly equal amount of sodium and chlorine? I know that the formula unit of salt is 1:1, but for example if there is 10000000 atoms of sodium is it possible that that there ...
Kevin's user avatar
  • 419
1 vote
1 answer
602 views

Detection of chloride anion

In a sample solution, containing $\ce{Cl-}$, while conducting the test for detection of $\ce{Cl-}$ ion first it is acidified with conc. $\ce{HNO3}$ then cooled and then $\ce{AgNO3}$ solution is added. ...
Tyto alba's user avatar
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