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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43
votes
7answers
81k 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 ...
7
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2answers
28k 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 ...
6
votes
2answers
169k 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 ...
9
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1answer
708 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. ...
3
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2answers
7k 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. ...
23
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4answers
46k 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 ...
25
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1answer
1k 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, ...
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-...
19
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2answers
10k 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
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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 ...
7
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1answer
5k 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 ...
9
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2answers
6k views

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 ...
8
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1answer
2k 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? ...
6
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2answers
930 views

Steam distillation- how it actually works?

To obtain phenylamine after it is formed from the reduction of nitrobenzene with tin, we carried out steam distillation. This is what I learned in class: "During the process,steam is injected into ...
6
votes
2answers
324 views

Scientific Reason for Salt Solution Gaining Volume

A little background to this question: my mom placed a glass with salt and enough water to just cover the salt in a room to "absorb negative energy" out of the room at her office. It obviously "worked"....
5
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1answer
23k 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 ?
2
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2answers
2k views

Using significant figures 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 $\pu{0.1 mL}$, or every $\...
2
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2answers
894 views

Reaction between copper (II)chloride and aluminium foil [closed]

When I reacted copper chloride and aluminum foil instead of getting the brown color I got green color. Can anyone share their procedure where the experiment actually succeeded?
1
vote
1answer
1k views

Can an iodine clock reaction work without using a strong acid?

I'm going to do an iodine clock reaction for a project and we had to submit the materials and safety sheets for the experiment a while ago. I thought I could do one by using hydrogen peroxide, sodium ...
1
vote
1answer
95 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
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1answer
4k 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?
58
votes
4answers
224k 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 ...
38
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5answers
61k 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 ...
31
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2answers
157k 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-...
24
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 ...
32
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 ...
7
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3answers
1k 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 ...
5
votes
2answers
513 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
1answer
1k views

Color imparted to flame and color of coordination compounds

When we heat a ionic substance/compound, the ionic bond gets weakened and the metal is ionized. Is the color imparted to the flame due to absorption of light? i.e. Do we see the remaining wavelengths? ...
3
votes
3answers
9k 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
5k 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
votes
1answer
5k 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 ...
4
votes
2answers
28k 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 ...
3
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1answer
10k views

Making carbon monoxide gas from formic acid and sulfuric acid?

Can I create carbon monoxide gas by just mixing formic acid and sulphuric acid together? Or do they have to be heated?
12
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3answers
12k 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 ...
10
votes
2answers
8k views

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 ...
9
votes
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 ...
8
votes
1answer
1k 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 ...
7
votes
2answers
2k 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 ...
6
votes
2answers
7k views

What are the reaction products of sulfur and potassium nitrate?

YouTube shows videos of dropping a piece of elemental sulfur into molten potassium nitrate and applying additional heat to accelerate the process. A white precipitate falls out to the bottom. There is ...
4
votes
2answers
2k views

Internal vs external steam distillation

To extract essential oils from plant matter (amongst other purposes), steam distillation is often used. I've seen a lot of different glassware setups for this. I've sometimes seen them broken into two ...
4
votes
1answer
136 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 ...
2
votes
3answers
198 views

Disposal of Silver Halides dissolved in Ammonium Hydroxide

I was reading the Lab Manual for Chemistry prepared by the NCERT . While going through the the test for Chloride ions (pg 88) I came across the following Hazard Warning : The solution obtained after ...
2
votes
0answers
165 views

Why is it difficult to measure the pH of environmental water samples accurately (near 7)?

I've read in several places (edit: 1, 2, 3, 4, 5, 6, 7, 8. 9, 10, 11, 12) that there are many practical factors that make accurate pH measurements of roughly neutral environmental water samples more ...
1
vote
1answer
137 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 ...
1
vote
1answer
34 views

Three Phases in TFM test instead of two

I am currently trying to perform the Total Fatty Matter (TFM) test on soap and for some reason I am getting three phases instead of two. The surfactant used is SLES and other reagents include hot ...
1
vote
2answers
32k 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?
1
vote
2answers
484 views

Why do increasing concentrations of zinc chloride not linearly decrease the freezing point?

I did an experiment on how different concentrations of $\ce{ZnCl2}$ affect the freezing point of demi water. My results were that till a concentration of about $10\ \mathrm{mol\,dm^{-3}}$ the freezing ...
0
votes
1answer
73 views

laser diode problem [closed]

I'm a student studying chemistry, i'm working with diode laser to look at emission spectra for certain complexes. i'm using integrating sphere as my setup, when i use the 405nm diode laser output of 4....
-1
votes
1answer
183 views

Electrolysis of Nacl with aluminium Electrodes

I conducted an experiment to find out the difference in products/ the final solution whilst using different electrodes. On using copper I obtained a teal blue soluble salt I believe to be $\ce{CuCl2}$ ...