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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40
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6answers
72k views

How can carbon dioxide be converted into carbon and oxygen?

How can $\ce{CO2}$ be converted into carbon and oxygen? $$\ce{CO2 -> C + O2}$$ Alternatively: $$\ce{CO2 + ? -> C + O2}$$ I'm aware that plants are capable of transforming $\ce{CO2 + H2O}$ to ...
5
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2answers
20k views

Why are NaCl and NaBr not soluble, whereas NaI is soluble in acetone (in the Finkelstein reaction)?

My book states that: Finkelstein reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium ...
22
votes
4answers
40k views

what kind of suspension liquid should be used with ferrofluid (so it does not stain the glass)

Please take a look at the following video: I am working on a new project, and I need to find whats the best liquid to hold ferrofluid inside the glass (or maybe even plastic) container, so that ...
6
votes
1answer
146k views

What is the reaction between oxalic acid and potassium permanganate?

I've already searched online some information about this equation, but everywhere I read, there's also sulfuric acid, which we did not use in the laboratory. We only used potassium permanganate and ...
18
votes
2answers
7k views

What exactly happened when I added KOH to hydrogen peroxide?

I recently added a potassium hydroxide, $\ce{KOH}$, pellet to a small droplet of hydrogen peroxide (30 %), $\ce{H2O2}$. You could clearly see the potassium hydroxide dissolving in the droplet when ...
9
votes
1answer
531 views

Belousov-Zhabotinsky reaction: questions about rate determining step, k and activation energy

In one of our lab courses, we performed a variation of the BZ reaction, the experimental procedure is outlined below: Experimental Procedure 10 mL of 3.0 M $\ce{H2SO4}$ was added to test tube T1. ...
6
votes
1answer
3k views

Concentration of NaOH to dissolve glass

I am doing a physics experiment in which it is required to etch the outermost glass layer from a coverslip (regular lab apparatus). What concentration of NaOH should be dissolved in water, and how ...
5
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1answer
17k views

Copper and hydrochloric acid

When hydrochloric acid is added to a sample of copper why does it look pink at first then form a pale blue solution ?
1
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1answer
63 views

Uncertainties after Averaging Trials [closed]

If I conducted 6 trials for a lab, all with the uncertainty of (+/- 0.1 mL)... After averaging the 6 trials to plot the results, what is the new uncertainty?
-1
votes
1answer
648 views

How many hydrogen bonds are formed by water and by HF?

How many hydrogen bonds are possible for $\ce{H2O}$, given that oxygen has two lone pairs? Is it 4 or 2? Related: why is it that HF forms only 1 hydrogen bond, given that HF has three lone pairs?
53
votes
4answers
178k views

Why add water first then acid?

From school, I remember a very important rule: first you need to pour the water and then the acid (when you need to mix them) not vice-versa. This is because otherwise the aсid becomes very hot and ...
34
votes
4answers
8k views

How are poisons discovered? Does someone have to die/be poisoned from it first?

How are poisons discovered? Does someone have to die/be poisoned from it first? Or are there other ways of discovering the harmfulness of a substance? Perhaps everything is tested on other animals ...
22
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1answer
644 views

Interlocked cyclic compounds

Being new to chemistry, there may ought to be some properties I couldn't understand fully. One of them being cyclic compounds. One particular question about this is, whether these cyclic compounds, ...
11
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1answer
4k 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-...
29
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2answers
122k views

What do the different grades of chemicals mean?

When purchasing chemicals from Sigma, Fisher, or wherever, there are often -grade's attached to their description like reagent-grade, technical-grade, analytical-grade, or more niche-sounding biotech-...
5
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2answers
334 views

What is the correct way to verify a structure's geometry, for example for benzene?

My goal is to compare a calculated bond length with experimental data. Benzene is obviously common enough to expect sufficient experimental data to be available for it on the internet. I have found ...
3
votes
3answers
6k views

dissociation of aluminum sulfate in water

I had a question as to what happens when aluminum sulfate is placed into water. After conducting research online, I got varied answers: some say that it dissociates into Al$^{3+}$ and SO$_4$$^{2-}$ ...
4
votes
4answers
3k views

How to figure out if the reaction proceeds via SN1 or SN2 mechanism?

I have been assigned with the task of figuring out whether a reaction is $\ce{S_{N}1}$ or $\ce{S_{N}2}$. The information that I have is, that the yield is dependent on solvent polarity. More ...
4
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2answers
26k views

Why use a salt bridge at all in an electrochemical cell?

I was reading about electrochemical cells and I really don't understand why a salt bridge is needed. Can't you just combine the solutions? I've found a lot of webpages explaining electrochemical cells ...
4
votes
1answer
238 views

Zero filling leading to increases in resolution (NMR)

Zero-filling involves adding data points with zero intensity to the end of an FID. According to this website https://www2.chemistry.msu.edu/facilities/nmr/handouts/DH%20NMR%20Basics.pdf zero filling ...
4
votes
1answer
3k views

Why should one perform an extraction with multiple small portions of solvent as opposed to one large portion?

I'm performing a liquid-liquid extraction on a 1 l water sample for GC analysis. The procedure calls for three extractions with 50 ml of dichloromethane. Would one extraction with 150 ml produce a ...
12
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3answers
7k views

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 ...
8
votes
1answer
1k views

How does the Mentos-Coke explosion work?

We all might have seen this in some videos or in real life. But how exactly does this work? What is the chemical reaction involved? And why is the reaction of Mentos with Diet Coke more vigorous? ...
8
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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 ...
7
votes
1answer
937 views

Vacuum distillation apparatus selection and configuration

I want to assemble a "hobbyist-level" vacuum distillation apparatus for extracting small volumes of "typical" solvents (e.g., water, alcohols, ketones, diols). I already have standard lab glassware ...
6
votes
2answers
896 views

Why a specific temperature for value of 1 calorie?

Everything in chemistry often comes with a strong reason and facts behind it, but I stuck in definition of $1$ calorie. My reference book define one calorie as amount of heat required to raise the ...
4
votes
1answer
80 views

Cooling down and heating of solution unexpectedly during cation identification test

While conducting qualitative tests for identification of cations in the given salt, I encountered this unexpected temperature change. Following are the steps of tests: Step 1: We made an aqueous ...
3
votes
2answers
6k views

Does a sulfuric acid/nitric acid mixture dissolve PTFE (ie. teflon)?

In our lab, we commonly use a mixture of sulfuric acid and nitric acid to clean borosilicate glassware. I'd like to clean some PTFE pieces in there, too, but not sure if they will dissolve or not. ...
2
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2answers
1k views

Using sigfigs when measuring with an instrument with marks other than powers of ten?

If an instrument does have markings that are powers of ten, then finding the precision of the instrument is easy. For example, if a graduated cylinder had markings for every 0.1mL, or every mL, or ...
1
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1answer
126 views

What chemicals are mixed together to cause chemoluminescence? [closed]

My brother is supposed to do a science experiment at school for an open house. We found an interesting experiment in which you pour several chemicals together, causing the resulting concoction to glow ...
0
votes
2answers
20k views

The dissolution of ammonium chloride

The dissolution of ammonium chloride is used to cool a container of water placed in the solution. It's an endothermic process. What absorbs the heat and what loses it?
30
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3answers
75k views

Chemistry behind Gale's coffee maker in Breaking Bad

Is there a scientific basis for the coffee making equipment which Gale Boetticher describes in Breaking Bad? He talks about maintaining the right conditions for bringing out the coffee flavor without ...
38
votes
5answers
44k views

Choosing the right condenser

What are the advantages and disadvantages of the various types of condensers commonly found in the laboratory? Obviously more intricate pieces of glassware are more costly but assuming they are all ...
15
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9answers
8k views

How can 30 ml of water be heated in less than 10 seconds?

How is it possible to heat a tiny amount (30 ml)[1] of water to a high enough temperature to make a coffee, in less than 10 seconds and possibly instantly? Most heaters that I know of heat water ...
20
votes
1answer
263 views

Is it possible create crystalline solvate of electrons?

Okay, I know that this reads ridiculous insane, but one can obtain solvated electrons by adding sodium metal to liquid ammonia solution. The chemical reaction as written in my inorganic chemistry ...
9
votes
1answer
8k views

How does Ostwald-Walker method work?

From searching online I found this: The apparatus consists of two sets of bulbs. The first set of three bulbs is filled with solution to half of their capacity and second set of another three bulbs ...
23
votes
1answer
2k views

How can an inexperienced chemist determine the chemical structure of a molecule?

I'm a fairly inexperienced, but nonetheless interested chemist, currently planning a small project for the coming summer: I want to isolate an unknown chemical from a plant and determine it's chemical ...
12
votes
3answers
28k views

Differentiation between zinc, aluminium, and magnesium ions in solution

If I have three aqueous ionic solutions in which I know that the cation is $\ce{Al^3+}$, $\ce{Mg^2+}$, or $\ce{Zn^2+}$, how do I find out which is which? I was thinking to add $\ce{OH-}$ in the form ...
6
votes
3answers
6k views

Is there a way to experimentally measure entropy?

I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for $\...
16
votes
1answer
5k views

Failed synthesis of aspirin due to excess sulfuric acid

Last week, I tried synthesizing acetylsalicylic acid - the reaction is shown below - using $\ce{H2SO4}$ as a catalyst. However, as the title suggests the synthesis failed as I used too much $\ce{H2SO4}...
13
votes
3answers
8k views

Why isn't dry CaCl₂ used to dry HCl gas instead of concentrated sulfuric acid?

In our chemistry books, it is said that concentrated sulphuric acid is used to dry $\ce{HCl}$ gas. But, concentrated sulphuric acid is a strong oxidising agent so, why isn't $\ce{HCl}$ gas oxidised ...
12
votes
4answers
15k views

How pure NaCl is typical table salt? How is it purified?

How pure $\ce{NaCl}$ is typical table salt? Is it pure enough for research-level experiments in chemistry? How is $\ce{NaCl}$ purified if need to be?
10
votes
1answer
3k views

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 ...
10
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2answers
1k views

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 ...
15
votes
2answers
1k views

Are PTFE stir bars resistant to all lab solvents?

It seems like glass-coated stir bars are a specialty item. Standard stir bars are coated in PTFE. Is PTFE resistant to all typical lab solvents? Or is there a reference to check to ensure it is ...
12
votes
1answer
15k views

Color changes of a solution of acetone and sodium hydroxide

I have put acetone and sodium hydroxide solution (approximately $\pu{1M}~ \ce{NaOH}$) in a beaker and didn't see any colour change for a day (actually, it was transparent, no colour). After almost 2 ...
11
votes
2answers
6k views

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 ...
10
votes
3answers
3k views

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 ...
9
votes
3answers
6k views

Bunsen burner and 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 ...
7
votes
7answers
15k views

Is there a simple and inexpensive way to generate nitrogen gas?

It's fairly easy to generate a significant yield of hydrogen gas simply by reacting zinc metal with $\ce{HCl}$ or aluminum with $\ce{NaOH}$ solution. But is there a simple and inexpensive chemical ...