Tag Archive: chemistry


If you’ve ever taken an organic chemistry lab class, you’ve probably done a melting point determination. That’s when you take a small sample of a solid, heat it up, and make note of the temperature at which it melts. This can be used to identify an unknown, but it is often used to assay purity. This is because impurities tend to make solids melt over a range of temperatures rather than at a single point, and because they tend to lower the melting point overall. There are fancy instruments you can buy which will measure melting points, but they’re so simple that I decided to make my own.

One way to do it is to use a Thiele tube, but I didn’t have one of those lying around. So I reached for my volumetric flask, filled it with mineral oil, and set it on a hot plate. Then, I put a tiny bit of the chemical vanillin into a capillary tube; this is my sample to test. I rubber-banded the capillary tube to a thermometer, such that the sample was next to the bulb. I set up a stand and clamped the thermometer in place, suspended in the mineral oil.

This would have worked, except that the samples used are typically so small that they are difficult to see with the naked eye. So I grabbed my USB microscope and clamped it in place, focused on the sample.

do it yerself

With my apparatus assembled, I turned up the heat and sat back to watch. Sure enough, between 80 and 82 degrees C. My copy of the Merck Index actually gives two melting point ranges for this compound, 80-81 and 81-83 degrees, which is a little confusing but seems to confirm that my melting point apparatus works as expected. Sweet!

melting

How did TopOc do on last year’s to-do list?

Not bad! As consistent readers might have noticed, the big news behind the scenes is that I have gotten involved in another production space, LumShop. Not only is it providing facilities for DIY Spectro development, it is also kindly hosting my chemistry lab! This will end well, I’m sure.

So what’s next?

  • Even more hard-hitting commentary and sass
  • More fractals and fungaloids!
  • Augmenting and measuring the concentration of hydrogen peroxide!
  • Third generation DIY Spectro!

Between this lineup and my lab, I’m sure the site will stay busy, but if you have any requests or suggestions, leave a comment!

dont forget the crystals

Magnesium sulfate crystals, clingin’ to a petri dish. Chillin’.

Another quick lab snap. These are some nice crystals I grew. I was washing an earlier, less photogenic crystal garden with alcohol, and catching the runoff in a petri dish. I let it evaporate and was greeted with this happy little accident! The crystals are magnesium sulfate, available as Epsom salt at most pharmacies.

haxor hijinx: a DIY hotplate

I have, once again, found myself at the helm of a DIY lab, this one with a chemical wetlab focus. I’m sure this will provide lots of material in the future; right now, I want to share a protip I came up with the other night. I have been using soda can alcohol stoves for heat, but this isn’t always appropriate. You can’t heat flammable mixtures, and they leave soot on my glassware. But I don’t have a hotplate yet! What’s a gutterpunk labnerd to do?

Don’t forget the boiling chips!

It’s won’t spin a stir bar, but a clothes iron will do fine as a hotplate! You can see that I’ve secured this one to the lab bench with wood and a clamp for extra stability.

 

 

dry ice in occupied durham

And what,

you might be asking yourselves,

have they been doing all these recent months instead of writing high-octane science friction and science fact here on the intarwubs?

Frozen carbon dioxide turns directly into a gas. How sublime! The dry ice is so cold that it causes water vapor in the air to condense, forming a fog.

Answer: All sorts of zany things! During a recent Really Free Market hosted by Occupy Durham, I had the opportunity to do another chemistry show.  Like the demonstration in my CO2 Problems video, I used soapy water and phenol red pH indicator to help illustrate the properties of frozen carbon dioxide. The color change is particularly dramatic, and is a good tie-in to the environmental effects of CO2. The greenhouse effect seems harder to demonstrate effectively – if anyone has a good way of demonstrating the idea, let me know!

“]

dry ice and phenol red, bubblin' away... { pix courtesy of Specious }

One thing I showed in this demo which wasn’t in CO2 Problems is the strange noises that dry ice makes in response to metal. If you try to cut a piece of dry ice with a knife, or press a paperclip into it, the ice will make a horrible screeching shriek. It’s most dramatic if you put a larger chunk of dry ice into a metal pot – it will scream and skitter around! My explanation? The warm, thermally conductive metal speeds up the sublimation of CO2 near its edge; the expanding gas pushes the metal away briefly and then the pressure buildup dissipates, bringing the metal back in contact with the ice. This oscillation makes the screeching noise. Try it out yourself and see if you think I’m right!

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