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

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Calculate accelerating voltage required to separate two particles in a magnetic sector analyser

So, in mass spectrometry we have the following equation to describe a magnetic sector analyser, $$\frac{m}{z}=\frac{B^2r^2e}{2V}.$$ Lets say that I have two particles with different mass/charge ...
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19 views

Fluorescence spectrocopy, sensitivity

lets say we increased the excitation wavelength higher than it should be, what effect would this have on the sensitivity on our analysis, or changing the emission wavelength to a higher value than it ...
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20 views

Fluorescence Spectra, emission spectrum

What exactly does the excitation spectrum tell us about a sample in Florescence Spectroscopy, what information does it tell us? I know that we will get an output of concentration vs intensity but ...
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33 views

An issue with Bouger-Lambert Law

I'm certain that I misunderstand this law. It states that: $$I = I_o e^{-kb} $$ and after rearranging: $$ A = ln{I_o}-lnI $$ where $A$ stands for absorbance. 1) Does is mean that when the ...
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1answer
148 views

Why is filter paper fluorescent?

Typical filter paper used in chemistry lab (e.g. Whatman #1) exhibits autofluorescence in near UV with excitation maximum at 365 nm and emission maximum at 440 nm. It was reported in literature[1] ...
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25 views

Why is NH4OH used in Polarimetric analysis?

Why is a sugar solution pre-treated with ammonium hydroxide before analyzing? And why is it specifically ammonium hydroxide instead of sodium hydroxide or calcium hydroxide?
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67 views

How do I perform a gravimetric analysis of Portland cement?

To determine the silica ($\ce{SiO2}$) content in Portland cement by gravimetric analysis it is digested in $\ce{HCl}$ and the silica residue is eventually measured. The chief constituents are ...
5
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89 views

Standard solution and extracted solution : same concentration?

Summary : I am currently testing how a certain type of foam adsorbs HAP, PCB and OCP, and to this end I am depositing some on the foam, then extracting it. To know how much was extracted, I need to ...
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97 views

Why is absorbance spectrum continuous and not quantized?

1) In text books, the absorption event is usually described by a figure shown below1: light excites electrons to higher states in atom or molecule. The difference between the ground state and the ...
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78 views

Are refractive or density based Brix meters better for use with alcoholic drinks?

Assume that somebody wants to measure the sugar content of a liqueur. It seems that there are two types of Brix meters for it, ones which use the solution density and ones which use refraction of ...
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44 views

Can F2/HF be separated using acid/base solutions in series?

I am trying to verify the results of EPA method 26A (http://www.epa.gov/ttnemc01/promgate/m-26a.pdf). The Method claims to be able to separate and quantify a mixed halogen/halide gas stream. Although ...
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98 views

A COSY NMR problem. How to draw the spectra?

Does anyone know how to draw (predict) a hypothetical COSY NMR spectra for AMX spin system (the spin of A M X nuclei is 1/2)? Thank you very much!
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53 views

A student is provided with 500 mL of 600 ppm solutions of fructose. What volume of this solution in millilitres contains 0.15 fructose? [closed]

A student is provided with 500 mL of 600 ppm solutions of fructose. What volume of this solution in millilitres contains 0.15 fructose? Does this mean that I just have to use 600 ppm as the ...
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31 views

What are the limits of analytical chemistry?

As I understand it, the branch of chemistry dealing with identifying substances present in a sample is called "analytical chemistry". This branch looks vast and complicated, with lots and lots of ...
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24 views

What are the products formed by a typical wood fire? [duplicate]

What are the products formed by a typical wood fire? I tested the ash from my fireplace and found it to be on the acid side. While this question has been partially answered in answers to another ...
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1answer
105 views

What is pre-concentration (context: Breath analysis)?

What is the meaning of pre-concentration both in general and specific to this context of a) "In addition to consistent sampling protocols,.. pre-concentration, ...
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61 views

Quantifying Ascorbic Acid in Soft Drink

I have access to a GC/MS, FID, and a spectrophotometer. My first thought was to derivatize with trimethylsilylating agent, then run it by GC. Unfortunately the water is problematic. Heating it is ...
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40 views

How to test oxalic acid in potatoes

How could you test that there's oxalic acid in potatoes.For example, what chemical reacts to oxalic acid and then what will happen if it reacts?
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17 views

surface sensitive techniques

is there a way to analyze the surface of a transition metal (chemical composition and possibly oxidation states) immersed in a molten KOH environment, while the metal is also under electrochemical ...
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372 views

Concentration of diluted sample based on absorbance curve

I have a plot of Absorbance (ABS) vs concentration, and the fit curve is $$ Y = 0.1081 x + 0.015 \\ R^2=0.9925$$ Y is ABS and x is concentration. I need to dilute ($1/100$) my sample to measure ...
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131 views

Interpretation of the following mass spectrum

I'm given the above spectrum. $M^+ = 102$, probably $\ce{C_6H_14O}$ or $\ce{C_5H_10O_2}$. I'm thinking of ethyl propionate. (that picture also shows the fragments I expect). I can account for the ...
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1k views

How do I calculate the cell voltage using the following half-reactions and solubility products?

$$\ce{Cu_{(s)}|CuI_{(s)}|I^{–}_{(aq)}||Cl^{–}_{(aq)}| AgCl_{(s)}|Ag_{(s)}}$$ The concentrations of $\ce{NaCl}$ and $\ce{KI}$ are at $0.120 M$ and $0.090 M$, respectively, in the following ...
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54 views

How to interpret a MALDI mass spectrum?

I have some questions regarding how to read a MALDI mass spectrum in a paper. I am a biologist by training, so I would like some analytical chemists to help me out. The researchers ran a western ...
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65 views

which are the possible ways to detect impurity in drugs?

I want some information regarding the protocol for determining any type of impurity in pharmaceutical substances or drug product. Which type of impurities can be identified by HPLC and MS? what is the ...
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96 views

Yellow precipitate in the presence of ammonium molybdate?

We had analytical chemistry experiments to determine acidic radicals from a mixture of two salts. After the chloroform-chlorine water test for distinction between halides $(\ce{salt\ solution + H2SO4 ...
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87 views

Shelf-life of solutions

If I prepare the silver nitrate solution or any other solution, how can I know the shelf life of this solution? I know that it depends on the stability of the substance, but maybe there is some ...
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3answers
200 views

How do we actually know the chemical structure of a compound?

If a compound is placed before you and you are asked to determine what it is and what it's structure is,how do you actually do that ? This might be a baby question for most of you but I am not from ...
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112 views

Analytical solution to first-order rate laws

Does anyone know the analytical solutions to the following rate laws: 1) $\frac{d\rho_W}{dt} = -\rho_W*(K_1+K_2+K_3)$ 2) $\frac{d\rho_T}{dt} = \rho_W*K_2 - (K_4+K_5)*\rho_T$ 3) $\frac{d\rho_C}{dt} ...
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50 views

What is the effect of temperature during Cryotrapping?

I'm working on a lab report that has some specific questions that need to be included. The lab work itself dealt with GC-MS. What is the effect of the temperature selected during ...
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1answer
93 views

What is the best way to detect the presence of tear gas?

I realise that tear gas can be several different things (Pepper spray / CS Gas / CR gas, PAVA, etc) Is there a good way to detect some or any of these in the air? Ideally using an electronic sensor ...
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46 views

Testing for Iron-Gall Inks

I have to bottles of Lamy blue-black fountain pen ink. It turns out that some months ago the composition of the ink was changed by the manufacturer and there is no difference in the package. Before, ...
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1answer
119 views

Analysis of a mixture of carbonate salts

We've got a mixture of carbonate salts. It's a buffer, used in fish tanks. How might we go about identifying the components and their concentrations? I suspect it'd be hard to separate some of this. ...
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252 views

Why do you need a strong base for a titration

For a titration, if you want to know the concentration of an acid you use a strong base such as NaOH. My question is; why you can't use a weak base for this purpose? Is it because the calculation ...
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108 views

Round Bottom Flask with Inner Coating

I am using a rotary evaporator to separate DCM (dichloromethane) from some nasty tars. Before the evaporation is completed, I stop the process and collect the remaining slurry. The slurry is then ...
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217 views

Does a rotary evaporator need a draft chamber and a vacuum pump?

I am using DCM ( dichloromethane) in my research, as a solvent. At the end of the day I have to separate the salute and measure it. Up until now, I have been using a constant temperature oven, set a ...
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74 views

Glassware Test Instruments CAD blocks library

I am designing a fairly simple distillation for dichloromethane. Being an engineer I feel more comfortable working with precise dimensions of both the separate glass vessels (condensers, evaporators, ...
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906 views

(How) Does ICP-OES determine the quantity of detected elements, or just their occurance in the sample?

ICP-OES is a very common analytical method (Wikipedia page here), and I have heard a number of times (from chemists, too) that it is used for quantitative analysis. However, from the description of ...
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55 views

What analytical methods are used to quantify C, O, N, and H in a sample?

A very common analytical method for detection of more than 70 elements is ICP-OES (Wikipedia page). But apparently, it's not suited for some substances (cited from this paper, section 6.2, page 12): ...
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1answer
830 views

How are samples prepared for analysis with ICP-OES? Can it analyse gases?

In ICP-OES (Wikipedia page), you introduce a sample into a very hot plasma and then run a spectral analysis on the resulting light emissions. Liquid samples are sprayed into the flame. From the ...
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189 views

large wavelength range and list of x/y numerical data points of elements

I'm trying to get a set of FTIR or (FTIR like range) x/y numerical data points for a couple of elements, namely Silver, Platinum, Palladium, Gold and Sodium. I've looked on line and found images ...
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508 views

1H-NMR problem. Why are these hydrogen equivalent?

Above is a $^1H$ Nuclear Magnetic Resonance (NMR) spectrum for benzyl alcohol. The hydrogen in the alcohol group gives rise to a unique signal. The two hydrogens in CH2 give rise to a unique signal ...
3
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1answer
296 views

How is the time for a test tube in a centrifuge determined?

I came across some hairy math that's used for analytical centrifugation, mostly for things like determining the sedimentation rate for liquids. However, what I don't understand is how someone ...
3
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1answer
184 views

How can I find pKa from a titration curve?

I am fully aware that the pKa is the pH at half the equivalence point, but are there some programs or methods I could use to accurately estimate the pKa without manually drawing lines on the graph?
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197 views

Understanding the rate of change in titration curves

As I am looking at titration curves, a few things stand out. For now, I have a two part question: When titrating an acid with a base, for instance, the pH rises more or less abruptly around the ...
6
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1answer
453 views

Extracting elemental ratios from X-ray photoelectron spectroscopy (XPS)

Is it possible to extract information on elemental ratios from X-ray photoelectron spectroscopy (XPS)? For example, I am reading a paper and in it they say that the carbon to oxygen (C:O) ratios of ...
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546 views

How were elements and molecular formulæ determined in the old days?

Before modern chemical techniques, say in the 19th century and earlier, how did (al)chemists determine whether a substance was an element or a compound? If it was a compound, how did they determine ...
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403 views

How does temperature affect the concentration of flavonoids in orange juice?

I am in high school, and I would like to do an experiment on this for a project. I've done quite a bit of research into the different methods I could use (see 2.4.2 here) but I still cannot find ...
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1answer
249 views

Test presence of oxygen > 1%

I want to qualitatively test for presence of oxygen within argon gas. I would like the test to be positive if approx 1% or more is oxygen, but definitely negative if less than 0.1%. Anywhere between ...
4
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62 views

How do you determine the amount of acrylamide in foods such as baked fries?

There are many food studies which determine the concentration of a substance in a food item. For example, this study determines the concentration of acrylamide in solid foods like fries. By what ...
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91 views

How does a BET device function?

This is the theory behind BET. The theory is comprehensible My question is more geared towards what is physically and chemically happening within a BET device to get a reading? How does a BET ...