MIT Chemistry Behind the Magic: Mirror Mirror
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00:00
ChemistryPharmacy
00:35
Chemical experiment
00:45
Chemical experiment
00:55
Drop (liquid)Chemical experiment
01:09
Chemical experiment
01:17
Chemical experiment
01:33
Chemical experiment
01:40
SolutionAmmoniumGlucoseMixtureSodiumSilver nitrateWaterAmmonium nitrate
01:58
Base (chemistry)Sodium hydroxideSolutionSodiumSolutionBase (chemistry)Water
02:19
SolutionAmmoniumMoleculeSodium hydroxideGlucoseSilverLecture/Conference
03:25
Chemical experiment
03:32
Chemical experiment
03:45
Chemical experimentLecture/Conference
03:56
Chemical experimentLecture/Conference
04:09
SilverChemical experimentLecture/Conference
04:19
Chemical experiment
04:24
SolutionBase (chemistry)Sodium hydroxideSilverRedoxOxideKetoneAldehydeAldehydeGlucoseKohlenhydratchemieSetzen <Verfahrenstechnik>Wine tasting descriptorsCarbon (fiber)MetabolismChemical reactionWaterReducing agentProcess (computing)ChemistryCobaltoxideHydrogenMetal
06:16
Computer animation
Transcript: English(auto-generated)
00:08
I'm Jessica, and today I'm going to be talking about a chemical demonstration I like to call Mirror, Mirror. In this demo, MIT's Dr. John Dolan will demonstrate Tollens' test, a chemical test
00:22
created by this man, Bernard Tollens, a German chemist born in the late 1800s. So let's watch Dr. Dolan perform this demonstration here at MIT as part of the Cambridge Science Festival. Okay, so I'm going to be careful, and I'm going to pour my first substance into the
00:45
flask, my second substance down to the last drop, and my third substance.
01:28
And we're going to do a little shaking. We're mixing some things together.
01:42
So what did Dr. Dolan do? Well, he added three solutions to the flask. Solution one was glucose in water, solution two was a mixture of silver nitrate and ammonium nitrate, and solution three was sodium hydroxide,
02:00
which is a base. So let's focus on the second two solutions first. When you mix solutions two and three, two things happen. First, you form Ag2O, which is insoluble in water, so it precipitates out as a brown solid.
02:21
The sodium hydroxide reacts with ammonium, NH4+, to produce ammonia, NH3. This dissolves the precipitate, and you end up with AgNH3 too, which all has a positive charge.
02:41
This is soluble in water, and it's called Tollen's reagent. Now, the positive charge is borne by the silver. So what we have in solution is essentially silver ions. Now, looking at solution one, glucose looks like this.
03:03
We don't really care about this whole part of the molecule, so we're going to call it R for the rest. So glucose is basically this. And this part of the glucose is going to start reacting with the silver ions.
03:24
Let's watch what happens. I don't think you see anything happening, do you? OK. Still working on it. I'm getting tired here.
03:40
Something happening? Oh my goodness, I can see myself.
04:07
Well, this is a real workout, I'll tell you. So what we've created here is a beautiful silver mirrored flask.
04:25
So look at that. Dr. Dolan has created a beautiful silver mirror. It almost looks like a Christmas tree ornament, and a silver ornament could, in fact, be made this way. So here's what's happening. Electrons from here, the glucose, get transferred to the silver,
04:41
reducing it to silver zero. Silver zero is insoluble in water, it's just silver metal. And it's precipitating out on the inside of the flask, forming the beautiful silver mirror that we see.
05:00
Now, this process is called reduction. And whenever something is reduced, something else is oxidized. So the glucose must be getting oxidized. It becomes this, and oxygen was added here. Now, this process is similar to metabolism in our bodies.
05:22
We remove electrons from the sugar we eat, and transfer them to the oxygen that we breathe. In a reduction reaction like mirror mirror, there might be energy released. In your body, this energy is harnessed in chemical bonds, stored for later. The point of Tallin's test was not to produce silver mirrors,
05:41
although a similar reaction is used for that today. The point was to distinguish between two types of sugars, ones containing aldehydes, and ones containing ketones. Let me draw those. The difference is that in an aldehyde, the carbon is connected to a hydrogen,
06:01
and in a ketone, the carbon is connected to another carbon. Aldehydes are more reactive than ketones, so they will react with the silver ions, while the ketones will not. That's it for me. Hopefully you enjoyed this video, and I will see you next time.
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Series of 13 media