A giant silver mirror

A giant silver mirror


This is just the Tollen’s test for
reducing sugars on a large scale but the resulting silvered flask is most
impressive. The quantities here that we’re going to use are appropriate for a one or two litre, one or two cubic decimetre, flask but
they can be scaled up or down as appropriate. The most important thing
to remember about this experiment is the flask must be scrupulously clean
if we are to get a good silver mirror. The best procedure is to
clean it with detergent and a brush, rinse it out with water followed by concentrated nitric acid and
several rinses with distilled or deionised water. We start with 150 cubic centimeters of 0.1 moles per cubic decimetre silver nitrate solution. We add to this a drop at a time some 880 ammonia. We get a brown precipitate first, which, on adding more ammonia, will eventually redissolve, to give a clear solution. It’ll take about five cubic centimetres of 880 ammonia. We now take 75 cubic centimetres of 0.8 moles per cubic decimetre potassium hydroxide Again we get a brown precipitate of
silver oxide. And we add more 880 ammonia to this a drop at a time again until the precipitate redissolves to give a clear solution. This solution is ammoniacal silver
nitrate. It contains silver plus ions complexed
with ammonia molecules. We now put the ammoniacal silver nitrate into the flask we’re going to silver and add to it 12 cubic centimetres of 0.25 moles per cubic decimetre glucose solution. Glucose is a
reducing sugar and will reduce the silver ions to
metallic silver. The solution will start to go brown or
grey and at this point it’s important to keep
moving the solution around the flask so that the whole of the
inside of the flask is constantly being wetted. Over a period of a couple of minutes a silver mirror will begin to form on
the inside of the flask. I stress it’s vital to keep the solution moving around so that the whole of the inside of the flask is exposed to the silvering solution. The chemistry of this process was
actually used in the past to form the silver coating on mirrors,
looking glasses. A giant Christmas tree decoration. When you finish this demonstration it’s important to dispose of the spent ammoniacal silver nitrate solution as quickly as possible. You should do this by pouring it down the sink and flushing it with plenty of water. Ammoniacal silver solutions have been
known to explode if they are left standing for some
considerable time, for example overnight. Therefore it’s vital not to put the residues in a silver residue container. For the same reason it’s not appropriate
to make up the ammoniacal silver nitrate solution any considerable time before the demonstration and certainly not the previous day for example.

39 Comments

  1. 75 cc from 0.8M of KOH or NaOH ? Nice video…
    How many cc finally used about Ammonia? 5 cc when you added Ammonia to Silver SOlution, then when you added OH- how many ?

  2. In the experiment silver mirror is created, it's also called the silver mirror experiment. Why would you call it silver glass?

  3. 2Na2SO3 + 4AgNO3 –> 2Ag + Ag2SO4 + SO2 + 4NaNO3
    This can be also done, but make sure to heat test tube without boiling the solution…
    This is reaction for identifying SO3 2- ions in the solution 🙂

  4. I like how he wears gloves. You'll spend ~$200 for lab grade chemicals. +$50 for beakers, etc. $1000 for a fume hood.

  5. I can't tell which one is more fascinating: the reaction itself or the guy who is doing it while he reminds me of Jeff Daniels in Dumb n Dumber.

  6. Question: Will there be any difference if I put the Potassium Hydroxide to the Silver Nitrate solution first, then the Ammonia?

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