| Pages:
1
2 |
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Displacement of silver by copper in nitric acid
Hi, Since I lost about 4 grams of silver the first time around I do not want to make a mistake with my larger piece of silver. Hence this question:
At the moment I have plenty of silver precipitated out of solution via copper. Now the reaction is still ongoing very very slightly with plenty of
what now is quite clearly a very less dense precipitate (what is precipitating now has the same bouyancy as the solution, it tends to float rather
than sink straight away like the precipitate of the first few hours did); Question. Is it possible to still have silver in the copper/silver nitrate
solution that will not be displaced by the copper because the copper does not have sufficient nitrate left to dissolve and kick the silver out for
want of better words?
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
Hexavalent
International Hazard
Posts: 1564
Registered: 29-12-2011
Location: Wales, UK
Member Is Offline
Mood: Pericyclic
|
|
Theoretically, the reaction would continue going until you ran out of either the silver nitrate or the copper. You can speed up the reaction somewhat
by gently heating, and adding more copper to your mixture.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Quote: Originally posted by Hexavalent  | | Theoretically, the reaction would continue going until you ran out of either the silver nitrate or the copper. You can speed up the reaction somewhat
by gently heating, and adding more copper to your mixture. |
Thanks Hexavalent, I just wanted to be sure. I have a dark green solution of copper nitrate, PH2, and a blue solution, PH3, of copper nitrate from
the previous silver precipitation experiment, am I right in assuming that the greener one is far more saturated with Cu2+ complex than the blue one? I
am just curious.
Also can I titrate in order to discover how much copper there is.
And I read somewhere ages ago that I can use Ammonia to discover whether there is any silver left in solution. Now I know this will be minimal since
I ran both experiments to their completion, IE overnight, I added two drops of ammonia into a test sample from each solution and immediately saw a
bright deep blue just before dissolving. I also diluted a test sample and then added drops of ammonia from a syringe; the first few drops produced a
milky reaction before the next few drops which then turned to that bright deep blue. I would like to understand more of what is happening, it's not
essential for my photography, but I want to learn since this can only benefit my appreciation for investigating off-shoots and links to various
reactions. thankyou.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
kadriver
Hazard to Others
Posts: 196
Registered: 7-11-2012
Location: United States
Member Is Offline
Mood: Thankful
|
|
I know this is an old thread, but I could not resist adding some input since I am new to this forum.
CHRI$25,
It looks like you may have had excess nitric acid from the dissolution of the silver - this will cause the silver mud (it is actually called cement
silver because it looks like cement) to float as you described earlier in this post.
What is happening is as the silver "cements" out from adding the clean copper to the silver nitrate solution, the excess nitric acid begins to
immediately redissolve the cement silver. globuals of cement silver get full of gas as it dissolves, causing the globuals to float.
I have encountered this problem and this is what I did to solve it.
Use just enough nitric acid per gram of silver to dissolve it. This will ensure that most or all of the nitric acid will be consumed during the
reaction and your cement silver will have a bright crystaline appearence. Plus you save nitric acid for use with other experiments.
When you dissolve silver metal with dilute nitric acid, first weigh the silver and then use that weight to calculate the amount of nitric acid you
will need to completely dissolve the silver.
It takes about 1ml concentrated nitric acid to dissolve 1 gram 925/sterling silver.
It takes about .7ml concentrated nitric acid to dissolve 1 gram 999 fine silver.
To dissolve, first put on a pair of nitrile or latex gloves, silver nitrate stains skin on cantact for 3 or 4 days. Then put the silver in a beaker
and cover with a watch glass.
Using the numbers from about, calculate the amount of nitric acid needed to completely dissolve the silver - keeping in mind that the amount needed
will be different for pure silver (999 fine) and 925/sterling silver.
Then use this calculated number, and add that amount of DISTILLED water to the beaker with the silver in it. Don't use tap water because it frequently
containes dissolved chlorides (chlorine) and this will combine with the silver nitrate to form silver chloride in your reaction vessel causing loss of
your metal.
After adding the calculated amount of distilled water to the silver, replace the watch glass and place the container on low heat.
Measure out the calculated amount of nitric acid and begin adding a few ml of nitric acid to the container with the silver and distilled water. Add it
slowly and incrementally using a pipette. As the reaction slows, add a little more acid until the silver is completely dissolve. I like to have a tiny
piece or two of silver metal left in the bottom of the reaction vessel. This acts as an indicator to let me know that all the nitric acid has been
consumed.
The key here is to let the reaction take its time. Fresh acid will make the reaction move along much quicker, but then it is much easier to over shoot
the acid - the very problem we are trying to avoid.
If there is a few undigested pieces of silver left, then what you can do is pour off the silver nitrate solution, and add drops of nitric acid to the
remining bits to dissolve them completely.
A small amount of free nitric acid is required in order to get the silver to cement out onto the copper. If the nitric is completely consumed, then
the copper will not react and it will just sit there with no silver forming on it. If this happens, then add a few drops of concentrated nitric acid,
stir with a glass rod, and re-introduce the copper.
925 and sterling silver, when dissolved in dilute nitric acid, will produce a blue to greenish solution due to the copper and nickle.
999 fine silver should produce a clear colorless to faint pale yellow colored solution with no traces of blue or green.
When cemeting silver with copper, you can tell when the reaction is complete when the silver no longer forms on the copper. As long as silver
continues to form on the copper, there is still silver in solution. When complete, the copper will appear bright pink after all the cemented silver
has been shook off of it. Unless there are platinum group metals present, these metals will also cement out, usually at the very end of the
cementation process. They will appear as black powder adhereing to the copper and sometimes cling stubbornly to the copper.
Another test to see if all the silver has come out of the solution is this: draw a sample of the solution though to contain silver and add a few drops
of hydrochloric acid or a few grains of table salt to it. If silver is present, then a cloud of silver chloride will form very quickly. It the
solution stays crystal clear, then it is safe to conclude that all the silver has been removed.
Hope this helps anyone looking to work with silver.
kadriver - edited once to add weight information
[Edited on 7-11-2012 by kadriver]
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Kadriver - This is very very helpful indeed. thankyou for taking the time to explain something. At least now I understand the floating situation. I
extracted 20g of silver second time round and only lost about 3 to 5 grams this time. The second time worked very well without any floatations this
time and I learned the HCL test a few days later after the first test, and it was clear of silver. So all in all I was able then to get my silver
nitrate. But your explanation has 'cemented' a few lose ends, your technique I will try next time round. But the first time yes indeed I had too
much NO3, not due to calculations, but due to the fact that I mis-calculated the amount of alloy copper in the sterling silver.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Purifying Silver Nitrate
Had a spot of bother re-crystallizing silver nitrate and was wondering now if I had done it correctly, I found only one old reference to this on the
web. My method was simply to re-dissolve in distilled water and evaporate through very gentle heating, but my result is now different from the
remaining silver nitrate that I have from the original reaction. Namely the crystals are white and very tiny, colour is white and texture a bit like
sugar, whereas the silver nitrate crystals from the initial reaction that I did not re-dissolve are translucent and the crystals are bigger/chunkier.
I tried to find references that would help me at least to know what I should expect to see from re-crystallizing but could not.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
woelen
Super Administrator
Posts: 8012
Registered: 20-8-2005
Location: Netherlands
Member Is Offline
Mood: interested
|
|
I think that your fine crystals are quite good. I have commercial AgNO3 and this also is white.
The original product consists of larger crystals and usually these crystals look more like glass or ice. The smaller the crystals, the more white the
solid looks like.
|
|
|
MrHomeScientist
International Hazard
Posts: 1806
Registered: 24-10-2010
Location: Flerovium
Member Is Offline
Mood: No Mood
|
|
Really the difference is just due to growing conditions. If you let your solution evaporate on its own, without heating, over a much longer period of
time, you'd get larger crystals that would be more in line with your commercial sample. I've done this myself. Woelen is right in that your smaller
crystals would look more white simply because they are smaller, and have more surfaces to reflect light.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Both of you thankyou. I appreciate that you took the time to help. I was a bit concerned that I might have contaminated somehow - a spot of rain
fell for a few minutes even though the reaction was 75% covered outside, managed to cover it after a minute or so but was worried. Silver nitrate
being precious could not afford to throw away and start again.
So, unable to find info on this topic, I need to ask why re-dissolving and evaporating purifies? What would the chemistry behind this be? Why would
the crystal structure change like this? Sorry I can not work this one out by myself. Maybe if you have any references I could read then that would be
appreciated.
[Edited on 11-1-2013 by CHRIS25]
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
watson.fawkes
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by CHRIS25 | | So, unable to find info on this topic, I need to ask why re-dissolving and evaporating purifies? What would the chemistry behind this be? Why would
the crystal structure change like this? |
Recrystallization (a term for which you can search) is a
purification process because the compound being purified has more affinity for the crystal structure than impurities do, that is, if you're lucky.
Some impurities co-crystallize; for these, recrystallization doesn't work.
When you say "crystal structure", you have a terminology problem. Crystal "structure" refers to the microscopic, geometric arrangement of the
molecules in a lattice. The macroscopic shape of the crystals formed is referred to as the "crystal habit" (another term to look up). Habit is an
interesting topic in it own right. The most obvious change of habit is that larger crystals, as a rule, are the result of slower evaporation.
Impurities in the solution can change the habit, as well.
|
|
|
AJKOER
Radically Dubious
Posts: 3026
Registered: 7-5-2011
Member Is Offline
Mood: No Mood
|
|
As many silver salts are sensitive/reactive upon exposure to sunlight, and also to CO2 and sulfides as present in air, exercise caution. Your
purification attempts may actually be counter productive.
|
|
|
CHRIS25
National Hazard
Posts: 951
Registered: 6-4-2012
Location: Ireland
Member Is Offline
Mood: No Mood
|
|
Thanks watson fawkes. I can always count on you to highlight the nitty gritty details of things that would never occur to me. Irritating as it can
feel, I actually appreciate your little illucidations and have learned a great deal from you.
AJkoer, thankyou, that is something I had considered - but from the little I read seemed for photographic purposes that this was an absolute must -
the silver nitrate needs to be purified, now I know that I will never get absolute purity, Bakers analysis style if you are familiar with that, but
having synthesized this silver nitrate from its silver copper alloy, (two serviette rings), I knew that the initial product would certainly not be
pure enough for the old photography that I do (1840-1860). Since it will be mixed with ferric oxalate (which I still have to make) and tartaric acid
(which I have made) in such small amounts I am hoping that it will not degrade its effectiveness in noticeable ways.
‘Calcination… is such a Separation of Bodies by Fire, as makes ‘em easily reducible into Powder; and for that reason ‘tis call’d by some
Chymical Pulverization.’ (John Friend, Chymical Lectures London, 1712)
Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. (William Penn 1644-1718)
The very nature of Random, Chance development precludes the existence of Order - strange that our organic and inorganic world is so well defined by
precision and law. (me)
|
|
|
bfesser
|
Threads Merged
11-12-2013 at 16:14 |
bfesser
|
Threads Merged
11-12-2013 at 16:17 |
bfesser
|
Threads Merged
11-12-2013 at 16:21 |
| Pages:
1
2 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
