Hello! Today's experiment will be presented by Dimitris, just like every experiment.
I would like to inform you about how you can get yourself a t-shirt like this one..
..in order to support our channel.
More information in the description of this video.
And now I have to go to watch World Cup, because if I miss a second of the match, I will become Astatine!
Not stable!
This is Bernhard Tollens, my dear viewer.
Unfortunately, he is not here for an interview due to technical reasons..
..but he is here for a very beautiful reaction.
Here he is, mister Tollens himself.
Solution of ammonia and silver nitrate..
..Tollens reagent in other words.
Tollens reagent is made by mixing silver nitrate AgNO3 solution..
..and ammonia NH3 solution.
Its preparation is made only in lab, because Tollens reagent has limited life duration.
From production to consumption.
Just like my mother's macaroni pie.
Tollens reagent is used to determine the presence of specific organic compounds.
If the organic compound reacts with Tollens, then black Silver Ag precipitate or mirror of Ag will be formed.
This means that the organic compound contains an aldehyde group.
This!
Which is known as CH=O.
On the other hand, there is Fehling reagent or "feliggio ygro" (in Greek).
I am curious to know who translated that way Fehling reagent in Greek.
Blue Fehling solution is prepared by mixing together copper II sulphate crystals CuSO4..
..and sodium hydroxide NaOH in water.
Fehling is also made only in lab for immediate use.
It also reacts with aldehydes and copper I oxide Cu2O brown-red precipitate is formed..
..as you can see, my dear viewer, because you are not blind.
Actually, you cannot see the brown-red precipitate Cu2O.
You are not blind.
No Cu2O precipitate is formed yet, we have to wait a little longer for the reaction to take place.
Later..
Wwwwwwwell, still no Cu2O..
..which means that Fotis instead of mixing Fehling with aldehyde solution..
..he mixed it with an other solution and this solution was solution of acetic acid CH3COOH.
But mistakes are made to teach us.
- What did you learn from your mistake, Fotis?
- That this is the reason for which the whole lab stinks. I used acetic acid instead of methanal.
- Yes, and?
- I guess you will not invite me for another experiment? I don't know.
- This is for sure.
- You also learnt that Fehling reagent does not react with carboxylic acids.
- Maybe Fehling reacts only with aldehydes.
- Anyway, that glass over there contains methanal HCH=O.
-But how will you be sure that the glass contains HCH=O, Fotis?
- Eeeeem, I don't know. Could I smell it?
- You should taste it! Aldehydes and especially methanal, are extremely carcinogenic.
- Then how will we know for sure that this glass contains methanal?
- I think I asked this question in the first place.
- Anyway, you will add Fehling in the glass and if there is a reaction, you will see brown-red precipitate Cu2O.
- So, this means that the glass contained methanal HCH=O.
- You took it from my mouth (Greek expression).
- Yes, because you were ready to drink it. Add!
2 minutes later..
Half an hour later..
One hour later..
One day later..
Here is brown-red precipitate Cu2O, my dear viewer!
Which proves that the glass actually contained methanal HCH=O.
Methanal reacted according to this chemical equation.
This is how aldehydes react with feliggio ygro..
..I mean with Fehling reagent..
..which was named after Hermann Fehling, who discovered it.
Here he is!
At this point, I would like to introduce to you my students..
..Fotis and Eleni, who perform today's experiments.
What a plot twist, my dear viewer, don't you agree?
You didn't expext this, right?
Experimenting before presenting the stars.
How cool is that?
Well.. OK..
And now that professional directors, who watch this video..
..drank the remaining HCH=O or alternatively spilled it in their eyes..
..we may proceed to Tollens reaction.
Mixing Tollens reagent with HCH=O solution black Silver precipitate Ag is formed, as you can see.
Nothing interesting at all.
I think Fehling's precipitate was better, it was brown-red after all.
But, if the solutions' concentrations are very low..
..this reaction will form mirror of Ag.
The reaction's speed will be low..
..because of the low concentrations..
..and Ag will be slowly coated in the spherical flask's inner wall.
This is the equation of the reaction that takes place.
After some manual stirring..
..Ag finally created a thin layer on spherical flask's wall [half an hour later]..
..and now, Eleni and Fotis can admire the result and their faces in the mirror of Ag.
Fehling and Tollens reactions are a real pain in the ass school reactions.
We tried to show these reactions to you in a more pleasant way..
..so that you can see for yourself the brown-red precipitate Cu2O..
..and the mirror of Ag..
..that your school chemistry book says about.
Also, aren't these reactions a bit nicer now?
Of course not! They were like shit before, they are like shit now!
I am Dimitris and these are my students, Fotis and Eleni.
See you in the next video!
- Well, I have not said a single word in this experiment!
- It's because you prefer theoritical lessons!
Không có nhận xét nào:
Đăng nhận xét