41 votes

Why isn't pressure filtration popular compared to vacuum filtration?

It's much easier to assemble a system that's safe under external pressure than one that's safe under internal pressure. Convex flasks and tubes resist external pressure better than internal pressure. ...
jeffB's user avatar
  • 1,592
26 votes
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What's this glassware?

The glassware shown is a drying tube. The bulb holds cotton or glass/quartz wool while the tube part holds a drying media such as anhydrous calcium sulfate to keep moisture out of the vessel during ...
A.K.'s user avatar
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23 votes
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What's the purpose of this vintage glassware?

This is Geissler potash bulbs (German “Geißler’schen Kaliapparat”/“Kaliapparat nach Geißler”) designed and produced by Heinrich Geissler in 1860s and primarily used in the second half of 19th century ...
andselisk's user avatar
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22 votes

Does anyone know what this piece of glassware is?

I believe this is an ebulliometer, from the Latin ebullientem (to boil). It's a used to measure boiling points. Clearly, there are some spelling issues with the sharpie label here.
Zhe's user avatar
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22 votes
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Conventional heating compared to microwave heating of chemical reactions

Your question about the 'magic' microwave effect is one that I think most chemists who've used a microwave have asked. Anecdotally, some reactions do often just work better when carried out in a ...
NotEvans.'s user avatar
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22 votes

How is aqua regia stored?

How is aqua regia stored as it dissolves all metals? No one stores aqua regia for extended periods of time, because it decomposes rapidly, yielding volatile products that escape from the solution ...
paracetamol's user avatar
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19 votes

Unknown glassware

Oh, beautiful to be young :) This is a vacuum pump. You plug the top part into a water tap. There's a slit in the middle of the inner tube of this "condenser", it creates suction = vacuum when you ...
ChemistryHelpCenter's user avatar
18 votes
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What is the scientific term to describe the operation of a bong?

I think the term describing the initial process of separation of the solid phase (dust particles) from the gas phase via bubbling is a wet scrubbing process. On an industrial scale, it's more ...
andselisk's user avatar
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17 votes
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What are the plastic connectors called (for glassware)?

Those are called Keck Clips. 24/40 is the size of the joint.
DSVA's user avatar
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17 votes
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Why did my glass pot explode when I boiled sugar in it and added cold milk?

Assuming initially your glassware contained a cup of sugar and a little of water, you basically prepared caramel. Depending on the sugar employed, temperatures needed to trigger caramelization vary, ...
Buttonwood's user avatar
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17 votes

Why is there a bulge at the top of my volumetric flask?

From ASTM manual [1, p. 204], emphasis mine: Volumetric flasks should be diluted to just below the line, mixed thoroughly, then allowed to stand for 4 to 24 h to allow any heat from an acid-water ...
andselisk's user avatar
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17 votes
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How is polarization of light measured?

The instrument used is called a polarimeter. You basically shine monochromatic linear polarized light through a solution of known concentration and you measure the rotation of the light on the other ...
DSVA's user avatar
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17 votes
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Is it better to use a smaller, more accurate measuring cylinder several times or a larger, less accurate one for the same volume?

You have three types of errors: The errors in the accuracy of your measurement. Assuming you are reading the water levels consistently (at eye level at the bottom of the meniscus), these should be ...
theorist's user avatar
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16 votes

Why does KCl come in amber coloured bottles?

The potassium chloride solutions in my lab are in transparent glass bottles, as was the potassium chloride solution in my inorganic students’ lab at the LMU in Munich. If I recall it correctly, the ...
Jan's user avatar
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16 votes
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What is the "blue spirit" (or "red spirit") in mercury-free thermometers?

As per the Wikipedia page on Spirit Thermometers: The liquid used can be pure ethanol, toluene, kerosene or isoamyl acetate, depending on manufacturer and working temperature range. Since these ...
Avyansh Katiyar's user avatar
15 votes
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Why does KCl come in amber coloured bottles?

On a sample of one selling site, amber bottles are cheaper than similar clear bottles, for some moderate to large quantities, at least today. KCl is fairly cheap so when selling the stuff in small ...
davidbak's user avatar
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14 votes
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Why are Erlenmeyer flasks shaped the way they are?

Imagine a time when magnetic stirrers were unknown. You, or your lab assistant, would mix solutions in suitable glassware, shake manually, put it aside and then observe a change. An Erlenmeyer flask ...
Klaus-Dieter Warzecha's user avatar
14 votes
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pH probe bulb - what is happening within the glass?

My reference for all information and pictures is Harris' Quantitative Chemical Analysis, 9th ed., pp 347-9. I think it'll be worth your while to consult those pages, but I'll try to summarize the ...
a-cyclohexane-molecule's user avatar
14 votes
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400–430 degrees Celsius heated bath

If it doesn't specifically need to be a hydrocarbon, zinc metal melts at 419.5 °C. Could you do an "ice bath" of zinc chunks in molten zinc, maintaining the melt right at its melting point?
jeffB's user avatar
  • 1,592
13 votes

What is the "blue spirit" (or "red spirit") in mercury-free thermometers?

Another organic solvent used may be pentane. Perhaps the common ones contain toluene dyed with a red aniline dye . Other spirit filled thermometers variants include: Blue fill contains isoamyl ...
xavier_fakerat's user avatar
13 votes

Is there a simple way to distinguish grades of purity for copper metal?

It is unlikely that there is a simple method, not involving relatively expensive chemical analysis, for distinguishing 4N, 5N, and 6N copper specimens. Shown below is a photograph of some copper ...
Ed V's user avatar
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12 votes

Which is a more accurate scale for a chemistry high school lab - a triple beam balance or a digital balance and why?

A digital balance is much easier to use. I guarantee some of your HS students are going to have huge errors when using a triple beam because they don't know how to read it. That's not necessarily a ...
theorist's user avatar
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11 votes

How to identify a blow-out pipette?

Good to see classical analytical chemistry queries. These graduated pipettes or Mohr pipettes they are called, confuse even the relatively advanced users. First you have to check where the graduations ...
AChem's user avatar
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10 votes
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What are these upside-down glass egg-shaped containers for?

This is called an inverted specimen jar, sometimes called a sample jar, for obvious reasons intentionally designed to stand on the stopper (it is not a standard one to close the other jars in the lab)....
Buttonwood's user avatar
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10 votes

Why isn't pressure filtration popular compared to vacuum filtration?

Pressure filtration is commonly used in industrial applications outside of the lab. In this case vessels and process lines are usually made from metal or plastic and can be easily designed to operate ...
ChemEPhD's user avatar
  • 101
10 votes
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Sintered vs perforated plate Büchner funnels

The thing on the left is not usually a called a Büchner funnel, but a frit. Frits are generally meant to be used for stuff that can be redissolved afterwards, because they tend to clogg permanently, ...
Karl's user avatar
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9 votes

Choosing the right condenser

Soxhlet condenser There is one more type of condenser, quite rare and often forgotten: the globe-shaped Soxhlet condenser. Typically used as a reflux condenser. The vapors pass between the outer wall,...
andselisk's user avatar
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9 votes
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Preparing an inert atmosphere reaction vessel with only an input?

Her setup was wrong. There needs to be an outlet, the simplest solution in this case being a second needle with nothing connected to it, puncturing either septum to act as a vent to the atmosphere. ...
Nicolau Saker Neto's user avatar
9 votes
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Use of pipette during experiments for determination of oxygen by Winkler's method

[...] the pipette tip should be well below the surface of the solution [...] Usually, one would indeed keep the pipette above the solution to avoid that a (minor) part of the solution forms a drop (...
Klaus-Dieter Warzecha's user avatar

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