Thursday, April 10, 2008

Nitric Acid and Ethanol

Tonight we saw an episode of "The Simpsons" where Bart lets loose a python in the school chemistry lab. A flask full of ethanol is knocked over, followed by a flask full of nitric acid (labeled "Do Not Mix with Ethanol"). The combination forms a toxic gas.

The Simpsons is known for sprinkling math and science references throughout its scripts. (See Paul Halpern's book, right.) That's because many of the show's writers have advanced degrees in the subjects, including writer Bill Odenkirk, who has a Ph.D. in chemistry and George Meyers, who holds a degree in biochemistry from Harvard. In this episode, first aired last May, a math textbook gets shot and "bleeds" equations, and physicist Stephen Hawking makes an appearance in a flying wheelchair.

However, it turns out that the writers got this one wrong, as noted in this entry on tv.com:

When nitric acid & ethanol are mixed in this episode it produces a toxic gas. In fact, mixing these two chemicals will make a very explosive mixture, not a toxic gas.
Or if you don't care to rely on chemistry facts from a TV website, here's a more reputable source.

17 comments:

Charles said...

Actually, the Simpsons got that one right. A gas is DEFINATELY evolved - I know this from personal experience.

I frequently use a mixture of nitric acid and ethanol to clean my fritted filters. The procedure I use is to take a small amount of concentrated nitric acid (enough to cover the fritt) and add one squirt of ethanol to the nitric acid. At this point make sure there is a splash guard between you and the fritt. After a short (~10 second) delay, a violent reaction occurs where the mixture gets very hot and turns a brownish-red color, indicating the prodution of nitrogen dioxide (N2O), a gas. Some of this brown gas can be seen to go into the air (and hopefully the hood).

Pulling this mixture through the fritted funnel cleans it of just about everything! Be careful, though. Even after the mixture appears to be done reacting, don't put it in a sealed bottle. Even 100 ml in a gallon glass jug is enough to create a bomb powerful enough to shatter any adjacent glass bottles. (I learned that the hard way and am thankful no one was standing near it!)

A reference about gas evolution:
http://www.ab.ust.hk/sepo/tips/ls/ls005.htm
Here's N2O:
http://en.wikipedia.org/wiki/Nitrogen_dioxide

Dave P said...

Nitrogen dioxide (NO2) not (N2O)!

Charles said...

Yes, NO2. A typo, my bad.

Anonymous said...

I have never seen an episode of the Simpsons, however, they are correct in stating that a toxic gas is formed in the mentioned reaction. HNO3 is a strong oxidizer. When in solution, HNO3 oxidizes the ethyl alcohol (ethanol) resulting in NO2, a toxic brown gas. NO, another toxic gas, may also form, depending upon the concentration of the HNO3, among other factors. I went to the link posted; this is an excerpt from the Flynn index. Ethyl alcohol and nitric acid do form an unstable solution, but as mentioned above, they also form a noxious gas. If one is to conduct chemistry experiments, not to mention advise others on how to conduct chemistry experiments, he should know exactly what he is talking about. The ability to breakdown the components of a reaction and determine the products is a necessity when dealing with chemistry. As a chemistry major, and former homeschooled student, it bothers me to see the misinformation on this post, along with that on other posts as well. Perhaps if you are going to be an 'authority' on chemistry, and you do not possess a degree in chemistry, you should refer to other reputable sources (that excludes wikipedia)for your information.

Kathy said...

I am definitely NOT an authority on chemistry, as is stated many times on this blog. And I'm NOT encouraging readers to try this particular experiment. What I'm trying to do here is show how chemistry pops up in daily life, and show some ways the non-science person can look further into the science they run into.

The experiments I DO encourage people to try are ones that I've found on books and websites by and for teachers and knowledgeable hobbyists. When I list them, I've already tried them with my own kids -- successfully or not, but without incident. For the purposes of our homeschooling course of study, I'm more focused on actually handling and observing chemical reactions than the math. The math can come later, for those who are interested enough. You can get all the equations right and have no clue about the role chemistry plays in our world. I know, I did just that in public school!

But the bottom line is, this a blog, not a textbook! I am recording things we did and talked about regarding chemistry. That other families can benefit from our experience is all to the good. I link to the best information I can find in the 20-60 minutes I spend per blog post. Beyond that, you're on your own!

Charles said...

The anonymous poster would have done well to actually read the other comments as I already corrected what was mentioned in the post. Yes, NO2 (nitrogen dioxide), a toxic gas, is evolved. Furthermore, wikipedia entries need not be thrown out as invalid just because they come from wikipedia. In my research experience (I have a Masters in Chemistry and am close to my Ph.D. in Chemistry), wikipedia has very good scientific entries (so long as there isn't some politically charged topic discussed). The non-political Nitrogen Dioxide (http://en.wikipedia.org/wiki/Nitrogen_dioxide) entry is fine (and properly referenced).

Kathy said...

Actually, it was Nobel Prize-winning chemist Roald Hoffmann who told me he sends his non-science-major students to Wikipedia to look up new molecules they come across in everyday life.

It would be nice if the anonymous poster could take Hoffmann's cue and adopt a respectful attitude toward laymen who are at least TRYING to become better informed!

Anonymous said...

What a pretentious 'know-it-all' that 'anonymous' person who posted that information was. I personally also studied Chemistry A level when i was younger and got the highest mark in the UK ( i.e. 590/600), not that this information has much significance. I went on to study medicine after already doing a maths degree at Imperial College, London. Kathy was just commenting as a leyman about science in everyday life and maybe just suggesting 'user friendly' home experiments to encourage people to gain an insight into the beauty of science, in general. Whatever level a person is academically, one should always remember that at one stage, they also had no knowledge. Knowledge is just the application of the mind. It says nothing of the character or the heart of the person, which in my humble opinion, are far more important in life. Unless you're at the cutting edge of research in any field (particularly science), you are merely plagiarising other peoples discoveries and ideas. There is nothing 'smart' in that, when you really think about it. The true nature of 'genius' is original thought, which comes from imagination. Not the rigidity of closed, parochial automatons in so many universities around the world!

MyID said...

It's nice to know that The Simpsons gets its science right so often (remember Homer and Bart exploring other dimensions via general relativity?).

I'd like to suggest a fun chemical experiment that, although a bit dangerous, is nowhere as deadly as nitric acid experiments.

Obtain some potassium permanganate (used to be available for medical uses) and glycerin (glycerol), which is available in almost any drug store.

Make a small pile (one or two teaspoons) of the KMnO4. Be sure to make this pile inside a fireproof container (like a metal jar lid inside a sink or outside on the ground), surrounded by wet paper towels, and with adequate ventilation (don't breathe in the smoke).

Pour just enough glycerol to soak into the pile of crystals, then wait.

In a few seconds, smoke is seen. Then a beautiful flame and lots more smoke. It's great fun, especially the suspense from that initial delay.

This works because KMnO4 is a powerful oxidizer and glycerol is an alcohol just begging to catch fire. Mixing them creates an exothermic reaction (one that generates heat or other forms of energy).

Note: if you are not confident that you can handle fire, do not try this at home. Have a fire extinguisher ready just in case.

David

M M said...

How does 'Anonymous' (posting on April 2, 2009) manage to make quite such a claim as:

"I personally also studied Chemistry A level when i was younger and got the highest mark in the UK (i.e. 590/600)..."?

Not only are A-level 'marks' not disclosed to candidates (merely the grade); but how does he/she believe this 590/600 to be the "highest mark in the UK" - since national marks are not published either?

What a load of tosh some people talk when hoping to demonstrate their credentials on sites like this.

I look forwards to 'Anonymous' standing as a Member of Parliament in future - a career he/she is evidently already OVER-qualified for.

(Incidentally my own qualification for my assertion about A-levels is simple: I am an A-level examiner for a well-known Examination Board...in Chemistry.)

Nick said...

I am an A Level Chemistry teacher- I got told the marks out of 600 when I did my A Levels and my current students do too- however I have seen a few 595-598s and they never knew if they were the highest in the UK, I personally cannot believe 590 would be the highest in the UK. One student of mine was informed he was in the top ten for his year group, but that was for GCSE and not A Level.

Anonymous said...

Interestingly enough my student mixed nitric acid and ethanol by accident (he missed a wash step). I am not sure whether a gas was produced, but the result was an explosion, blowing out gas from the chemical fume hood he was working in...... Thankfully he had walked away just beforehand and no one was hurt.

pointblank said...

I love how that first anonymous guy said "I have never seen an episode of the Simpsons" hahahahah geez what a narc!

Anonymous said...

HN03 + CH3CH2OH -> CH3CH2NO3 + H20

This is the main reaction, but the solution must be cold for only ethyl nitrate to be produced, and as this reaction is strongly exothermic, its not very likely that this will be the only reaction occurring in the case of an accidental spill. The purported gas generated by the mixture is nitric acid decomposing by the heat generated by the formation of ethyl nitrate:

4 HNO3 -> 2 H20 + 2 N02 + 2 N0 + O2

Regardless, Nitric acid and ethanol DOES have a niche in that a mixture of these chemicals in water is used to etch metals, but even then, 10% nitric acid or above makes any mixture explosive.

Joseph Douglas Jewell said...

Totally an A+ narc Broham, anyone whoms been around a tv or computer or any other type of propaganda/entertainment device has seen the "Simpsons", the longest running show in history I believe.

Anonymous said...

I know that this bog is several years old, but here's a YouTube video of supposedly nitric acid + ethanol reaction:

http://m.youtube.com/watch?v=PzI1Dnz1wzE

Anonymous said...

As the poster about fritted glass funnels commented, I have also used this to clean fritted glass funnels, it works better than anything else.

I usually fill the clogged funnel halfway with nitric acid, concentrated, then add 1-2 drops of EtOH. There is a short delay in the reaction and it is highly exothermic and evolves a brown/orange gas-toxic. Do this in a fume hood with the sash down, I would also recommend a blast shield in front of the things you are cleaning just in case you have a shaky hand and drop too much EtOH into the nitric acid. Make sure your things are also clamped down.

We have used this reaction to even clean silver that had metalized in our frits out, from silver salts.