Questions tagged [experimental-chemistry]

This tag should be applied to questions relating to the theory, design, techniques or performance of chemical experiments. This includes but is not limited to theoretical structures, expected products, thermal calculations, and empirical analysis. Additional tags should be applied to narrow down the field of research.

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12
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2answers
2k views

In which country is it allowed to practice non-clandestine amateur chemistry? [closed]

I travel a bit so am flexible where I live, and have taken a recent interest in chemistry to try to gain an understanding of physical reality. I find learning from textbooks to be good, but want to ...
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How to remove a stuck stopper from a flask?

How do I remove a stopper that has been stuck in the neck of a 100 mL round bottom flask since I forgot to wipe the neck of the flask. A salt was formed in the 100 mL flask and the stopper ...
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1answer
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How did Michael Faraday melt Sodium Chloride?

Michael Faraday melted sodium chloride in a silver spoon and ran an electric current through the molten salt, which released chlorine as a gas and left pure sodium behind. Sodium chloride melts at $...
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1answer
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How do I calculate the concentration of sulphuric acid by a titration experiment with sodium hydroxide?

In my latest chem lab the objective was to create a primary standard of $\ce{NaOH}$ and use it to determine the concentration of sulfuric acid. The first part of the lab was determine the molarity of ...
12
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1answer
115 views

High temperature bath chemicals

I have an electric mantle that I want to bathe reaction vessels at temperatures up to $\mathrm{750^{\circ}C}$. Obviously that rules out oils. What substances are used as bath media at such ...
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3answers
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Why is the outermost part of the Bunsen burner flame not the hottest region?

Why is the blue flame the hottest on a Bunsen burner? I thought the outermost part of the flame must be the hottest region because of complete combustion of gases taking place there. Where am I ...
12
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2answers
6k views

Role of methanol in NaBH4 reduction

In reduction of carbonyls (aldehyde and ketones) to alcohols using NaBH4/Methanol, alkoxides are formed with the Boron which usually gets protonated on addition of water/acid. My question is what is ...
12
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1answer
6k views

Why do alpha-hydroxy ketones respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests?

I learnt from a certain textbook that aldehydes and formic acid respond positively to Tollens', Fehling's, Benedict's, Schiff's and HgCl2 tests. However, in another textbook I read that even alpha-...
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5answers
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Why do research papers mention experimental details in such detail?

The paper Analysis of cyclic pyrolysis products formed from amino acid monomer has the following to say in it's experimental section: Glycine, phenylalanine, tyrosine, tryptophan, serine, and valine ...
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Testing isopropyl alcohol purity

I'm curious how to test purity of isopropyl alcohol? I simply got very curious today. I bought rubbing alcohol and it doesn't say what's the purity anywhere. It could be 70%, but it could also be 90%, ...
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3answers
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Is argon preferred over nitrogen for maintaining an inert atmosphere?

I recently started a project in a new lab-group over Summer that does medicinal chemistry. Unlike in the undergraduate labs, they use argon instead of nitrogen for their inert atmosphere work. When I ...
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1answer
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What's the difference between precipitate and turbidity?

In many tests for various radicals, a "<color> precipitate" or "<color> turbidity" is mentioned. For example, lead ...
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2answers
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Proper use of vacuum pump during vacuum distillation

I am preparing to do a vacuum distillation and am unsure exactly how to manage the vacuum. The vacuum pump I have is a two-stage rotary vane pump which is capable of 250 microns or lower. It has a ...
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3answers
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How to check if azobisisobutyronitrile (AIBN) is still active?

I will have some samples of azobisisobutyronitrile and I want to perform Barton-McCombie reaction. The problem is that the reagent is quite old and I need to know whether it has not decomposed. Do ...
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799 views

Can atomic partial charges be measured in molecules experimentally?

Can we measure atomic partial charges in molecules experimentally? The charge of isolated ions can be measured, but when atoms are part of a molecule, the case is much more difficult. We do not really ...
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1answer
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What is the alternative to chromyl chloride test?

Chromyl chloride test is by far the best test to determine the presence of chloride ions in a salt because no analogous compounds are formed with fluorides, bromides, iodides and cyanides, so this ...
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1answer
203 views

A Question on the Role of Triplet Oxygen in the Formation of Artemisinin

It is observed that whereas singlet oxygen is required for an ene reaction with an alkene to give an allyic hydroperoxide, triplet oxygen will react similarly with an enol to give an alpha-hydroperoxy ...
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1answer
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What exactly is the Horwitz equation?

During a laboratory exercise in a course on analytical chemistry, we were asked to calculate the $z$-score. $$z=\frac{X_{\text{lab}}-X_{\text{cons}}}{S_{\text{target}}}$$ where $X_{\text{...
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2answers
357 views

Dissolving metal reductions

Could reduction of an organic compound by reacting it with sodium dissolved in $\ce{NH3}$ still proceed if a metal such as aluminium were used instead of sodium? I'm not sure about the aluminium amine ...
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0answers
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Is there a structured data source containing information on the World Health Organisation's Stability Testing Policies?

Hoping to automate some product testing guidance software, I've been attempting to find a (hopefully live, up-to-date) Database, Web-service, or other structured data source containing the ...
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2answers
8k views

What is the purpose of a boiling stick when heating a reaction mixture?

What is the purpose of a boiling stick when heating a reaction mixture? I read some stuff online and still don't understand how it works. Does it just ensure that the mixture will boil evenly? If so, ...
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3answers
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Water flow in condenser

How should the water flow in your condenser? From the flask to the top of the condenser, or from the top of the condenser back to the flask? I could imagine both: flask to top will fill the entire ...
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1answer
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What is the scientific term to describe the operation of a bong?

What is the scientific term for the separation of dust particles from air by suction through a specialized flask in a way similar to the operation of a bong? The thing that led me to this was a ...
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3answers
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Experimental calculation of solubility product constant

In order to calculate the $K_\mathrm{sp}$ of lead(II) iodide, I mixed $\pu{6.0 mL}$ of $\pu{0.01 M}$ $\ce{Pb(NO3)2}$, $\pu{6.0 mL}$ of $\pu{0.02 M}$ $\ce{KI}$, and $\pu{8.0 mL}$ of water, and a ...
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Can I pour a solution into another vessel with no air bubbles?

I have been trying to create a method to create a homogeneous agar solution. What are appropriate techniques to ensure homogeneous solidification of an agar-based aqueous solution? The new solution ...
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2answers
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Gas chromatography/mass spectrometry: Can I use peak ratios and molecular mass to derive quantity?

Can derive the quantity of a substance from a GC/MS report if I know: the ratio to another substance in the data, the quantity of that second substance, and the molecular mass of both substances. ...
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3answers
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How is drift due to static electricity eliminated from an analytical balance?

I've recently encountered a problem when using an analytical (0.1 mg accuracy) scale to determine the mass of a sample of ferrocene powder. The reading in the balance seems to drift either upwards or ...
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1answer
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What happens when I use cyclohexanol to prepare cyclohexene?

I've done a student experiment using cyclohexanol to prepare cyclohexene. We mix $10.5~\mathrm{g}$ cyclohexanol and $5~\mathrm{mL}$ $85\%$ $\ce{H3PO4}$ in a $50~\mathrm{mL}$ flask, then distill while ...
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1answer
981 views

C-F bond lengths of octafluoropropane using Bent's rule

I was trying to predict different $\ce{C-F}$ bond lengths of octafluoropropane, $\ce{CF3-CF2-CF3}$ : Applying Bent's rule here, we see that For $\ce{C^2}$, we have $\ce{C^3}$ and $\ce{C^1}$ ...
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2answers
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What is the chemical test for identification of benzophenone?

How to identify that a unknown compound is benzophenone? My working:- First I added 2,4- DNP(2,4-Dinitrophenyl hydrazine) to the compound. Yellow-orange crystals were formed which indicated presence ...
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1answer
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Calculation of Atomic weight percentage in AAS

I am currently doing doping studies in a system similar to this ($\ce{A_{x}B_{1-x}}$) and I have to find atomic weight percentage of $\ce{B}$ element using atomic absorption spectroscopy(AAS). I have ...
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5answers
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Why is it obligatory to cool down the container of a sample to measure its mass in a lab?

We were doing an experiment about hydrated crystals and more precisely how to determine $n$ in $\ce{CuSO4.nH2O}$. After we heated the crucible we were to cool it down using a Desiccator. Then this ...
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2answers
7k views

What is the accuracy of medical syringes?

I am interested in both low and high volume syringes.
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3answers
637 views

MacGyvering a sealed tube

Is it possible (advisable?) to make a sealed tube by melting and twisting the end of a borosilicate test tube? One issue that I can think of is that the pressure might be too high if I then proceed to ...
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2answers
847 views

Sintered vs perforated plate Büchner funnels

I just bought a sintered-glass style Büchner funnel for some vacuum filtration tasks. There's two issues I'm having with it: Filter material, especially activated charcoal, ends up stuck in the glass ...
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2answers
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How to quickly cool a test tube without cracking it?

Is there a way to safely cool a heated test tube quickly without cracking it due to sudden thermal stress in the glass? One thing that I tried was blowing on it, cooling it in slightly lukewarm water ...
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4answers
30k views

Why should the temperature be maintained at 0–5 °C in a diazotisation?

I know that in a diazotisation reaction, the temperature should be carefully maintained within the range of 0–5 °C by use of an ice bath. Why is this so? How does the temperature affect the stability ...
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3answers
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Why pipetting with a 30° angle?

After seeing this youtube video, I was left to wonder why to use a $30^\circ$ angle between the flask and the pipette when emptying it. I can imagine it is important to touch the flask with your ...
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Why, in titration, is universal indicator not commonly used?

My teacher said that we always used indicators such as methyl red, methyl orange, litmus, phenolphthalein, etc. rather than universal indicator. I don't understand why, though, would not universal ...
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3answers
2k views

What is the correct name for this lab technique in crystallization?

Take a glass rod and rub vigorously the wall of the flask, the substance will crystallize out of the solution. Take a fire polished stirring rod and etch (scratch) the glass of your beaker. The small ...
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2answers
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Why lithium gives flame coloration?

Theoretically speaking, beryllium and magnesium does not give flame test because their atoms are comparatively smaller and the valance electrons are strongly attached to the nucleus. Therefore their ...
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3answers
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13C NMR spectrum only showing solvent

This is my first time taking a $\ce{{}^{13}C-NMR}$ spectrum and while I'm aware the signal to noise ratio is much lower compared to $\ce{{}^{1}H-NMR}$, I didn't realize it was quite this bad. I took a ...
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2answers
8k views

Dess–Martin oxidation work up

I'm doing an oxidation of an alcohol with Dess–Martin periodinane which works really well but having trouble with the work up. Doing this reaction with about 5 g of alcohol so the reaction ends up ...
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3answers
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Experiment to prove that water has air

In elementary school, there was an experiment to show that water has dissolved air, which involved boiling some water and observing the drops at the surface of the container, and this proved that ...
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1answer
867 views

Is it safe to condense water into a liquid nitrogen trap?

I'm trying to remove water from an imidazolium salt (i.e. dry the salt). However I want to know if it is safe to remove the water under vacuum. Is it safe to condense water into a liquid nitrogen ...
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808 views

Products of Lead(II) nitrate decomposition

It is known, that decomposition of Lead(II) nitrate is one of the ways of generating $\ce{NO2}$ for lab use. I recently did this in order to acquire $\ce{NO2}$ in liquid form (ambient temperature ...
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2answers
606 views

Use of pipette during experiments for determination of oxygen by Winkler's method

We were performing estimation of $\ce{O2}$ by Winkler's method and we were told by the instructor that while adding $\ce{MnSO4}$ and $\ce{NaOH}$ / $\ce{KI}$ the pipette tip should be well below the ...
9
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1answer
488 views

Photochemical reduction of benzophenone: why inverted flask?

I've come across an interesting protocol for photochemical reduction of benzophenone to benzhydrol (diphenyl methanol) with sodium alcoholate in alcohol, the 2nd protocol in https://prepchem.com/...
9
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1answer
6k views

Is there a means to measure pH without indicators?

I have created a solution that should contain hydroxide ions. Therefore, the pH > 7, but is there any way to roughly estimate the pH in absence of any indicator? Maybe using current, or checking ...
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1answer
1k views

Questions about Buffer System (Lab)

I will be doing a lab on Hydrogen Phosphate buffer system tomorrow and I have a few questions about the buffer system. I am not sure if my assumptions are correct. (1) What would happen to the rate ...

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