13enigma
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Electrodes don't decrease significantly after electrolysis
I have been using silver and copper electrodes in a solution of sodium chloride. I usually end up with silver chloride or copper chloride depending on
which is the anode. The anode slime I produce or the residue that comes off of the anode electrode (copper or silver) is quite a lot depending on the
duration it's on. So after an hour of electrolysis I end up with 70 grams of silver chloride or copper chloride. But the electrode loss is 5 grams
from a 1 ounce bar. What is going on here??????? Is it the tarnish build up that affects the reading mass? I ended up trying to get rid of the tarnish
with baking soda and aluminium. But the Loss of grams in electrodes is still.minimal. please do not think I'm lying. I really need help why this
happens.
<i>Edit by moderator : Removed unnecessary capitalization from the title</i>
[Edited on 6-24-2017 by gdflp]
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gdflp
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Thread Moved
24-6-2017 at 04:48 |
Metacelsus
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Is the 70 grams dry, and free of sodium chloride? For silver, 5 grams of metal (107.9 g/mol) should give 6.64 grams of chloride (143.3 g/mol). Excess
mass must be impurities.
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13enigma
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How does the math on that work? And is it the same with sulfides and oxides?
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13enigma
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And the loss of mass on the 1 ounce bar? Is that ok? I lost less than what was produced in the solution. Is that impure buildup.
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violet sin
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Mass Loss from the silver bar is indicative of the actual number silver atoms dissolved or eroded off. This loss can be described in moles, which is
useful to the chemist. Seeing as how silver chloride is only partially composed of silver, if a given number of silver atoms are consumed, the rest
of your weight is chlorine. AgCl requires both, so the product will weigh more than just the lost silver.
But after you finish calculating the projected weight of AgCl that should be produced, based on the silver lost from the 1oz bar., there may be
discrepancies high or low. Too much mass means you have contamination. Can't make more AgCl than the lost number of atoms allows. Too little mass
of you product, and some is likely dissolved as a soluble salt, mechanicall lost in transferring or bound in some other way. Metacelsus pointed that
out nicely for you.
Now if your real problem IS the minimal loss of silver, making a minimal ammount of AgCl product.. I would see if the surface of the silver bar is
passivated in some sense, or did you oxidize your Cl- ions to Cl2 gas, or maybe forgot to add chloride in the first place? Sulfides and
oxides will act similarly with respect to weight change based on empirical formula. But they may or may not allow the reaction to keep going the way
chloride does. If the formed crust is tenacious, it may not spall off the bar.
Try cleaning the bar with citric acid or sulfamic acid. Both work in my experience, to clean tarnish off silver.
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