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Chemistry says that we are are we supposed to heat boiling flasks, and not Erlenmeyer flasks. However, I can't find any information about this on Google. Is there a particular reason for this?

Is it just because we want to separate the purposes for our glassware, or is there an actual valid reason?

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    $\begingroup$ Can you cite the "Chemistry" which says it? Erlenmeyer flasks are routinely used for heating. $\endgroup$ – ssavec Apr 2 '14 at 8:11
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This really depends on what you mean by heating.

One of the main uses for Erlenmeyer flasks is for recrystallization, which of course involves heating the container and contents. Typically this is only moderate heating, such as over a steam bath or with a hair dryer. Some manufacturers specify that their Erlenmeyer flasks are ideal for heating applications.

Traditionally, boiling flasks have more uniform and thicker walls, which allow for much greater heating limits, and a more uniform heating distribution. They are designed to handle more intense localised heating, and manage thermal and physical shock distribution. Erlenmeyer flasks usually have thinner walls and greater wall thickness variation, and are less able to handle sudden thermal changes, such as heating with a high energy source like a Bunsen, or heat gun. Using them in this way may well lead to cracking, fracturing or worse, and is unsafe.

So, although Erlenmeyer flasks can be heated, they are not specifically designed for high temperature, constant heating applications. For this, you should use a boiling flask.

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In Essential Environmental Science: Methods & Techniques by Simon Watts,Lyndsay Halliwell I've found this:

enter image description here

This because his conical shape does not allow an uniform expansion and so the glass could break. Furthermore if you are heating substances that will leave a residue will be very hard to clean it.

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The conical shape of an erlenmeyer flask creates a sharp angle between the bottom and sides of the flask. Stress, be it from heating, cooling, mechanical shock, etc., is not as uniformly distributed across such an angular structure as it is in a spherically shaped flask. Hence, the erlenmeyer flask is more prone to cracking under stress than a spherical flask.

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Since most Erlenmeyer flasks are made with Pyrex glass, there should be no problem heating them up. I have been told not to heat volumetric flasks since the volume could change.

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