{Disarmed} Copper Wire And Silver Nitrate

nitration

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This week in lab, students performed electrophilic aromatic substitution (and here). Dissolution of 4-methylacetanilide in 70% nitric acrid gives mono nitration. There are two possible products. The acetamide is a ameliorate ortho/para director than the methyl group, and so 2-nitro-4-methylacetanilide is the major product of the reaction. The reaction was a bit touchy. In my lab, for the virtually part the reactions were carried out at room temperature. This resulted in the reaction non occuring! Almost every pupil got dorsum unreacted starting material, instead of production. The production is supposed to be a bright, crayon yellow solid. Other labs ran the reaction on low heat and got excellent results… But some students left the reaction on the heat too long or at also high of a temperature and the reaction decomposed into this ugly brown oil. So there is a very small-scale window for success in this reaction. For the first time this semester (!) students analyzed the reaction mixture by Sparse Layer Chromatography.

A brief safety warning. Nitric acid is a very strong oxidizer. It reacts explosively with readiliy-oxidizable small organic molecules like alcohols and acetone… acetone being of course what all skilful lab students rinse their glassware with earlier they start lab. At that place was an explosion in our department concluding yr as a result of improperly mixing nitric acrid waste material and acetone waste. Nitric acid MSDS here, incident written report on nitric acid explosion (non from our department) here (it's probably worth glancing through the other incidents on that folio as well), and video showing gas development from nitric acid oxidation (this time of copper) here – note how much gas is produced in a short amount of time. Imagine this in a airtight container. Go on watching the video till the end, as it actually makes for a swell demo in itself.

The demo for the week was the silver nitrate/copper wire demo. Silver nitrate (nitrate existence the conjugate base of nitric acrid… which is how I'chiliad relating this demo to lab this week…) dissolves readily in h2o to give a solution of silver nitrate. Just virtually everything silver nitrate touches gets stained blackness. Not immediately… only after exposure to light. For this reason, silver nitrate used to exist used in early photography. No stains for me, though information technology is always a business organization.

Dropping copper wire into the silver nitrate solution initiates a redox reaction betwixt the silver ion and copper metallic. The silvery is reduced to elemental silver and the copper is oxidized to copper(Two):

Cu(0) + 2AgNO₃ = Cu(NO₃)_ii + 2Ag(0)

The silverish crystallizes at the surface of the copper and the copper wire quickly becomes coated with a agglomeration of elemental silver. At the aforementioned time, the copper ions go into solution and the colorless solution turns a characteristic blue equally the concentration of copper ions builds. It's a pretty dramatic demo of a nifty redox reaction. I was testing the speed of the reaction before I went to lab (silver started to get visible within 30 seconds to a minute), and I ended upwardly leaving the copper wire in the silver nitrate while I went to lab. I came back several hours later on and the crystals had plenty of time to grow and were very nice looking. I let it go overnight to encounter how big the crystals would get. I took a picture show when I got to lab the next morning (click for larger). And so I collected the silvery in a scintillation vial to take home with me. The pictures are from my experience, Noel posted a picture show a while back as well, and there is a nice video beneath.

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