Sciencemadness Discussion Board - Nickel sulfate questions

Nickel sulfate questions

Jackson - 14-11-2018 at 09:48

Hi, I have a few questions about nickel sulfate. I am trying to purify nickel sulfate from a solution of nickel and copper sulfates from a nickel. I saw that nickel sulfate (Heptahydrate) is soluble in ethanol and copper sulfate is insoluble. My first question is, Is nickel sulfate formed from sulfuric acid and nickel metal in the form of a heptahydrate in solution. I assume it is but I just wanted to make sure. Secondly, I cannot find any solubility charts in ethanol for nickel sulfate. Is it more or less soluble as tempature increases or decreases. I have been crystalizing out the copper sulfate and I just added some ethanol and a very small ammount of copper sulfate precipitated. I filtered it out and now I have a solution of nickel sulfate, but none is crystalizing out. I have been crystalizing out the copper sulfate by letting the solution evaporate outside over about two weeks, going from 60 ml down to 40 ml. I added 10 ml of 60% ethanol (pure ethanol concentrated from vodka, not denatured) and have evaporated for 2 days so far. Do i just need to continue evaportating. I assume so but I just want to verify. Also, the copper sulfate only crystalized on the nickels left in the solution. No more crystalized out after I removed them. The ethanol did precipitate some copper sulfate though. Should I add a source of nickel metal to add a nucleation site?

Thanks,

Jackson

Hendrik - 14-11-2018 at 10:34

A very good method that could be used in order to separate the Cu2+ ions from the Ni2+ is based on their reactivity. As far as I know, even in aqueous solutions, magnesium will be able to displace the copper and the nickel from their sulfates (upon heating, obviously). Add magnesium until any kind of reaction stops. In this way, you will obtain fine powders of copper and nickel. Filter the powders, make sure they are completely dry and add hydrochloric acid. Upon heating, nickel is going to react with HCl, yielding NiCl2. Copper is unable to do that, as it is less reactive. You will obtain Ni2+ in solution and the copper will be left untouched. Filter the copper powder and you are going to obtain a pure sample of NiCl2. You are free to release sulfate ions in order to obtain NiSO4.

elementcollector1 - 14-11-2018 at 10:41

Alternatively, adding a strip or some similar solid piece of nickel should precipitate the copper out in single displacement, leaving the nickel in solution alone. According to the reactivity series on Libretexts, tin, lead, bismuth and antimony would all also work for this purpose (but would potentially introduce more ions to the mix, as well as be harder to find). It might require heating and shaking to ensure that a coating of copper doesn't prevent the nickel from reacting further.

Hendrik - 14-11-2018 at 10:41

Aditionally, there is no such thing as a "heptahydrate in solution". Nickel is going to react with H2SO4 even at normal temperatures, yielding NiSO4 (in solution). The heptahydrate is a solid, not a solution. Secondly, NiSO4*7H2O will become more alcohol-soluble if the temperature is raised (there are few exceptions which show retrograde solubility, some calcium salts which are naturally extremely-low soluble and neodymium salts). This evaporation method that you have been trying seems a bit sloppy.

Jackson - 14-11-2018 at 12:45

The reason why I ask about the nickel being a heptahydrate or not is because the heptahydrate is soluble in ethanol by the less hydrated forms are not. I know it is not a heptahydrate in solution but another way I could word it is when it crystalizes out will it be the heptahydrate or the hexahydrate.

Aqua-regia - 14-11-2018 at 13:06

No, forget this purification. Dissolve the contaminated salt and electrolysing it with inert kathode and anode. First all the copper deposited, your salt is pure NiSO4. The bluish green solution will turning in grass green.

Test of remained copper:

A small sample treated with conc. alkali hydrosulfit(Na2S2O5)soln, acidifying with muriatic acid, boilinga few minits, then add 10% KSCN soln. If no white precipitate observed, all copper is all deposited.

elementcollector1 - 14-11-2018 at 18:35

Electrolysis would require keeping the voltage between about 1.07 and 1.48 volts - below 1.07 volts, copper will not be reduced from solution, and above 1.48 volts both copper and nickel would be reduced at the same time. Remember, it certainly is possible to electroplate alloys.

I actually did my senior project on this, in fact - I was hoping to enrich a plated alloy from aqueous solution in rare earth metals. Turns out I accomplished the opposite. Made for an interesting research paper, at the very least.

Melgar - 14-11-2018 at 21:45

Coins that are pure nickel, for anyone interested in not having to deal with this annoyance in the future:

Canadian nickels, pre-1982
Canadian dimes and quarters, pre-2000
French 1/2, 1, and 5-franc coins, pre-Euro adoption

Anyone aware of any other common coins that a typical SM member might have laying around?

unionised - 15-11-2018 at 12:39

Quote: Originally posted by elementcollector1

Electrolysis would require keeping the voltage between about 1.07 and 1.48 volts - below 1.07 volts, copper will not be reduced from solution, and above 1.48 volts both copper and nickel would be reduced at the same time. Remember, it certainly is possible to electroplate alloys.

I actually did my senior project on this, in fact - I was hoping to enrich a plated alloy from aqueous solution in rare earth metals. Turns out I accomplished the opposite. Made for an interesting research paper, at the very least.

What is it about electrode potentials?
I mean, why does nobody understand that the voltage depends on the concentration of ions?

So you can't meaningfully say things like "Electrolysis would require keeping the voltage between about 1.07 and 1.48 volts".

clearly_not_atara - 15-11-2018 at 13:01

Copper oxide dissolves in excess alkali; nickel hydroxide does not. So copper and nickel can be separated by adding an excess of potassium hydroxide -- enough to solvate any Cu2+ as K2Cu(OH)4.

This is probably easier than electricity.

unionised - 15-11-2018 at 13:20

Quote: Originally posted by Jackson

Hi, I saw that nickel sulfate (Heptahydrate) is soluble in ethanol

Jackson

Really?

CharlieA - 15-11-2018 at 17:25

I thought for electrolysis, the voltage for a reaction was determined by the entities, and the current was proportional to the concentration of ions. No?

Aqua-regia - 17-11-2018 at 09:08

Does no matter for low voltage if you want do do it for preparative purpose. If you working betw 1-2 Voltage, it "evolving" very low amperage. This means, your process will take a very very long time. It would only help to generate pointless timewasting. Okay,some nickel run to waste,but insignificant.

Many years ago dissolved an old Ni-Cu small pot and electrolysed with 10V /8A

Time to time analysed the soln, after te copper ions disappearded, stopped . Total time for electrolys. was almost a day!

unionised - 17-11-2018 at 09:13

Quote: Originally posted by CharlieA

I thought for electrolysis, the voltage for a reaction was determined by the entities, and the current was proportional to the concentration of ions. No?

No
https://en.wikipedia.org/wiki/Nernst_equation

unionised - 17-11-2018 at 09:22

Quote: Originally posted by unionised

Quote: Originally posted by Jackson

Hi, I saw that nickel sulfate (Heptahydrate) is soluble in ethanol

Jackson

Really?

I checked.
It isn't soluble enough to visibly colour a test tube of alcohol.

fusso - 17-11-2018 at 09:58

Quote: Originally posted by unionised

Quote: Originally posted by Jackson

Hi, I saw that nickel sulfate (Heptahydrate) is soluble in ethanol

Jackson

Really?

I checked.
It isn't soluble enough to visibly colour a test tube of alcohol.

I wonder how this false claim ended up on wiki?

unionised - 17-11-2018 at 10:00

No idea.
I suspect the chloride dissolves in alcohol.

unionised - 17-11-2018 at 11:14

Incidentally, if I wanted to remove a small amount of copper from a solution of nickel sulphate, I'd add potassium iodide.
That will remove the copper as CuI.