Questions tagged [analytical-chemistry]
The branch of chemistry concerned with identifying and quantifying the chemical constituents of matter.
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Calculating amount of base needed to achieve a specific pH in a mixed ethanol-water solvent
I'm looking for some way to calculate how much base I will need to add to an unbuffered solvent consisting of a mixture of ethanol and water in order to basify it to a specific reading (10) on an a pH ...
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9 views
Positive or negative error using FAAS
if we want to determine the quantity of zinc in an insulin formulation, we make standard solutions for the measurements and we also have the physical samples. In standard solutions it contains water, ...
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21 views
How can you distinguish between 1°, 2° and 3° alcohol by the means of turbidity? [on hold]
How can we distinguish between 1°, 2° and 3° alcohol by the means of turbidity ?
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18 views
Measurement of concentration during a given reaction to determine rate laws [on hold]
The constant measurement of concentration is required to find the rate law of a certain reaction. In an integrated rate law, concentrations are measured as a function of time. How do you measure the ...
19
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2answers
2k views
Does ultrasonic bath cleaning damage laboratory volumetric glassware calibration?
As an analytical chemist, I'm always ensuring my glassware is thoroughly clean before I start an analysis. However, my supervisor always states that using ultrasonic bath to clean volumetric glassware ...
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0answers
21 views
Calculating Sensitivity in Mass Spectrometry
My mass spectrometry textbook gives the following example:
Calculating sensitivity Magnetic sector instruments are specified to have a sensitivity of about $4 \times 10^{-7} C \ \mu g^{-1}$ for the ...
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0answers
16 views
Procedure for determining the levels of Acrylamide from a cup of coffee
For experimental purposes, I want to determine the level of Acrylamide in cups of coffee. Is there a method that doesn't use spectrometric analysis to determine it as I do not have access to it in the ...
12
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3answers
979 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 ...
2
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1answer
28 views
Evaluate indicator choice (phenolphthalein)
A student wishes to find the concentration of a $\pu{50 mL}$ solution of acetic acid $(K_\mathrm{a} = \pu{1.8e-5}).$ He performs a titration using a solution of $\pu{0.2 M}$ sodium hydroxide. The ...
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29 views
Comparing the emission spectrum of ethanol and mixture of alcohols
Sorry if this question has a simple answer, but I've been unable to find it elsewhere.
Using a diffraction grating, burning ethanol (99.9%) will produce a rainbow of colours. However, when burning ...
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1answer
47 views
How can I figure out if my store bought chlorine is the percentage it says it is?
Chlorine is an important part of maintaining any pool. I've read horror stories of people buying chlorine from pool stores or big box stores and the chlorine being ineffective.
If stored long enough ...
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0answers
27 views
Acid and base separation on an anion exchange column [closed]
I'm new with this concept and so I would need some advice.
I want to separate an acid and a base in a water solution. The acid has $\mathrm{p}K_\mathrm{a}(\ce{HA}) = 5$ and the corresponding acid of ...
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2answers
558 views
Testing thermite for chemical properties
I'm writing a movie in which a bunch of military explosive ordnance experts destroy a turbine with thermite and the local fire chief has to work out whether it is plain $\ce{Fe2O3}$ and aluminium ...
3
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3answers
43 views
Applying vacuum at the end of a flash chromatography column
I know that flash chromatography uses a positive or pushing pressure to achieve the goal which is separation. Would the same goal be achieved if you had a vacuum on the other end instead of a ...
1
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1answer
25 views
What is responsible for the smell of incomplete hydrocarbon burning and what sensor can detect it?
After I pass the smoke from partially burned fuel oil through a filter, I can still very strongly detect the smell. It is the same thing you smell from the exhaust when an old car or truck goes by.
...
11
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3answers
673 views
Why are isotopes an issue in reading mass spectra?
It is my understanding that the isotope distribution for carbon and hydrogen, for example, are skewed heavily toward one species, i.e., one isotope accounts for ~99% of the abundance of the element in ...
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30 views
What does “at%” mean and how it differs from “mol%”?
Sorry if my question is a bit obvious, but for some reason I'm getting confused with the percentages in this question:
Concentration of $\ce{A}$ is $\pu{80 at\%}$ and concentration of $\ce{B}$ is $...
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1answer
35 views
Redox titration or iron(II)
The concentration of $\ce{Fe^2+(aq)}$ can be determined by a redox titration using
A. $\ce{KBr}$
B. $\ce{SnCl2}$
C. $\ce{KMnO4}$ (basic)
D. $\ce{KBrO3}$ (acidic)
Can anyone please ...
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0answers
21 views
how to liquefy crude oil wax?
We have crude oil sludge which contains about 40% wax (paraffin wax).
My concern is how to liquefy the stated sludge by adding suitable solvents but in very less quantity so that the process should be ...
8
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0answers
45 views
Quantitative Transfer of Volatile Standards
(Edited w/ updates) Okay, long story short I work in a lab which has been working on cannabinoid analysis (in the licensed Canadian market) and have had a lot of issues surrounding the standards/...
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2answers
54 views
How do I convert salinity measured in mg/L Cl into parts per thousand as NaCl?
I have collected water data using a refractometer that records salinity in ‰ (parts per thousand) as $\ce{NaCl}$. I want to compare my data to other data but every journal article I read has the ...
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0answers
25 views
Measuring pH in ferric oxalate solutions
I have a problem with measuring $\mathrm{pH}$ in ferric oxalate solutions ($\sim 5~\text{to}~\pu{10 g L-1}$ $\ce{Fe},$ $\pu{0.8 M}$ oxalic acid, $\pu{25 °C}$). While I am sure about the $\mathrm{pH}$-...
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1answer
30 views
In HPLC, how does column diameter affect the retention time?
I am using a smaller diameter column than my previous one keeping all other factors such as stationary phase, solvent, solvent gradient constant. (Obviously, flow rate will be less in smaller column). ...
3
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2answers
115 views
Why should AAS use element lamps?
AAS (Atomic Absorption Spectroscopy) is a quantitative analytical technique used to measure very small concentrations of ions in substances. The main idea is that the sample is atomised in a flame and ...
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1answer
32 views
How to find volume needed from a stock solution
I am making a media that is amended with substrates after being autoclaved in order to keep the media anaerobic. In order to do this, we make stocks of the solutions from a known concentration. I am ...
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0answers
22 views
Molar absorption coefficient for potassium hydrogen phthalate
I would like to draw a comparison of the sensitivity between several spectrometers. Therefor I measure the absorption of a serial dilution of potassium hydrogen phthalate (KHP). The idea is to compare ...
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2answers
46 views
Finding molarity of hyposulfite solution used in titration
$\pu{0.1 g}$ of $\ce{KIO3}$ is treated with excess $\ce{KI}$ solution. The liberated iodine required $\pu{44 ml}$ of $x$ molar hypo solution. Calculate the value of $x$.
I have used the equivalent ...
14
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1answer
1k views
Using a gas stove instead of Bunsen burner for a flame test?
In all chemistry labs we use the Bunsen burner. What's the difference between it and a good old gas stove used in home? Can the stove also be used to get positive flame tests for some cations (like $\...
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1answer
54 views
Flame test color for non-ionic compounds
What color would a non-ionic compound, such as $\ce{NH4OH}$ or $\ce{HCl}$, produce in a flame test? Is no color produced, or is it different for each compound?
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2answers
60 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 ...
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1answer
39 views
Volume of 0.5 M HCl needed to make a 10 % 500 ml solution
What volume of $0.5\ \mathrm M$ HCl solution is needed to prepare a $500\ \mathrm{ml}$ $10\ \%$ concentration solution, whose density is $1.05\ \mathrm{g/cm^3}$.
I've started off with finding the ...
2
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1answer
39 views
Does hydrochloric acid change in concentration over time?
I have new bottles of 1 N hydrochloric acid from Fisher. The acid comes standardized from the company:
Standardized at 25 °C to pH 8.2 against sodium hydroxide that has been standardized against ...
3
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1answer
57 views
When to run a blank using ICP-MS
I am currently writing a paper for my Advanced Analytical Chemistry course, and the topic I am writing on is the analysis of Arsenic in drinking water. The EPA's literature describes how to perform ...
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18 views
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 ...
0
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1answer
89 views
What defines a proton as “labile” in NMR? [closed]
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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0answers
20 views
Determination of pKa and molar absorptivity coefficient using spectrophotometry [closed]
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
31 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
55 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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26 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
57 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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2answers
107 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 ...
2
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1answer
125 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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17 views
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
61 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 $\...
0
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1answer
39 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
62 views
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
38 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
18 views
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
74 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 ...
8
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2answers
286 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 ...
