Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
0
votes
0answers
44 views
How does salts which cation has acid feature and anions has basic feature depends only by the correlation of their costants? [on hold]
My book is not very explicative about it, i'm trying to get the equation:
$$[\ce{H^+}]=\sqrt{K_w\times\dfrac{K_{a}}{K_{b}}}$$
but i didn't succeed, can someone explain the theory behind and how to ...
0
votes
0answers
15 views
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 ...
1
vote
1answer
21 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-...
-1
votes
0answers
21 views
How can I precipitate metal ions from a solution? [on hold]
I'm in Grade 12 Chemistry. We're doing some solubility, and one of the things we need to be able to do is explain a procedure where we separate metallic ions from a solution. So, for example, how can ...
1
vote
1answer
14 views
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, ...
9
votes
2answers
55 views
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 ...
-1
votes
0answers
24 views
Determining chemical formula of the hydrocarbon via combustion analysis [closed]
A container of volume $\pu{15 L}$ contains a hydrocarbon at $\pu{27 °C}$ and $\pu{2 atm}$ pressure. For the analysis, we take $\pu{10 g}$ of hydrocarbon and the pressure becomes $\pu{1.718 atm}$ (at ...
2
votes
0answers
28 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 ...
-1
votes
1answer
20 views
How do I prepare 100 mg/ml pesticide solution from 100 mg liquid standard? [closed]
Recently I bought a Malathion from Sigma. It is 100 mg but is in a liquid state and its volume is not mentioned in the vial. I have to prepare 100 mg/ml pesticide solution standard. How should I do it?...
0
votes
1answer
12 views
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?
1
vote
0answers
26 views
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 ...
0
votes
2answers
40 views
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?
0
votes
1answer
42 views
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 $\pu{40 mL}$ ...
1
vote
0answers
27 views
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. ...
-1
votes
0answers
15 views
Qualitative Inorganic Analysis - Cation test
I remember learning in my tenth grade about Cation test using Sodium Hydroxide and Ammonia Solution (I mean these tests http://spmchemistry.blog.onlinetuition.com.my/2012/08/identifying-cations-test-...
0
votes
1answer
33 views
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 ...
0
votes
1answer
13 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 ...
1
vote
1answer
17 views
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 ...
1
vote
1answer
21 views
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 ...
-1
votes
1answer
22 views
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}...
-1
votes
2answers
18 views
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 ...
2
votes
0answers
52 views
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, $j$ ...
-1
votes
0answers
32 views
Is it possible to use too much precipitant? Or precipitant that is too pure?
When carrying out a precipitation in the laboratory, is it possible to either use too much precipitant? Or perhaps a precipitant that is too pure?
For example, when using ammonium hydroxide, is it ...
1
vote
1answer
26 views
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 ...
2
votes
1answer
33 views
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 ...
1
vote
1answer
28 views
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 $\...
0
votes
1answer
139 views
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?
1
vote
0answers
21 views
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 ...
1
vote
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 ...
0
votes
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 ...
2
votes
1answer
74 views
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,...
3
votes
1answer
77 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, ...
-1
votes
1answer
29 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.
...
0
votes
0answers
41 views
Stoichiometry based on chemical equations
A $\ce{21.1 mg}$ sample of a mixture of glycine $\ce{CH2NH2COOH}$ and benzoic acid $\ce{C7H6O2}$ yields $\ce{N_2}$ at $\ce{730 torr}$ at $\ce{21°C}$. This $\ce{N_2}$ displaces $\ce{5.235g}$ of mercury ...
0
votes
0answers
17 views
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 ...
0
votes
1answer
64 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 ...
2
votes
3answers
487 views
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 ...
0
votes
0answers
29 views
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 ...
8
votes
3answers
111 views
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 ...
4
votes
2answers
38 views
Does ICP-OES detect molecules in suspension?
I'm curious whether ICP-OES has the ability to detect molecules in suspension?
4
votes
1answer
137 views
Mathematical explanation of blank titration in Mohr method for argentometry
In my book it is written that in order to minimize systematic error in Mohr method for argentometry it is a common procedure to conduct a blank titration with $ \mathrm{Ag^+} $ against a $\mathrm{CrO_{...
0
votes
0answers
35 views
Internal standard calibration in GC/MS
The experiment is about quantification of di-n-octyl phthalate(DNOP) in PVC flooring material using fluoranthene-d10 as internal standard, and TA sent me this data and asked me to draw standard curve ...
3
votes
1answer
52 views
Is the pressure in an HPLC system the same throughout?
I'm not sure if I'm articulating myself well enough, but here's my problem: I have a current HPLC system, where we typically have backpressure readouts of around 15 MPa. We are looking to get a new ...
0
votes
0answers
37 views
Capacity of buffer
I want to dissolve 23 mg of EDC (N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride) in MES buffer with pH=6. How can I know the amount and concentration of MES buffer which can keep the pH=...
2
votes
0answers
33 views
Why are signals broadened in polarography?
In the attached polarogram from Heyvrovsky's 1959 Nobel lecture, transitions from one plateau to the next are smoothened out rather than sharp and abrupt. Why is that?
I understand that currents were ...
0
votes
0answers
38 views
How does the “sample type” selection on the MassHunter software for Agilent 7900 ICP-MS affect the quantitative results?
I'm new to using the instrument, and recently I have tried to measure Cr in both the eluent(1% nitric acid) and a method blank (also 1% nitric acid, but after it has gone through the entire analytical ...
0
votes
1answer
56 views
marijuana testing process [closed]
Does anyone know a bit about how costly and accurate are the current THC measurement techniques?
Please speculate what drives cost chemicals, consumables or instrument time.
-1
votes
1answer
43 views
What's the identity of the crystalline solid in the following reaction? [closed]
A mixture of toluene, benzoic acid, aniline and phenol was dissolved in diethyl ether and extracted with 5% $\ce{NaHCO3}$ solution? This extract was acidified until a white crystalline compound ...
2
votes
0answers
30 views
How does activated carbon catalyse oxidation?
Context: I am doing an experiment on the quantitative analysis of ascorbic acid in a blackcurrent syrup using fluorescence spectroscopy. In order to do so, ascorbic acid was first oxidised into ...
0
votes
0answers
34 views
Why are the results of two methods different for calculation LOD and LOQ?
I calculated the Limit of Detection (LOD) and Limit of Quantification (LOQ) with results (Table 1) obtained from HPLC (spiked muscle sample). For this purpose, I used regression analysis and two ...
