Sciencemadness Discussion Board

Purify calcium nitrate

TmNhRhMgBrSe - 13-5-2020 at 23:36

I make calcium nitrate but solution is yellow. How to remove yellow colour?

B(a)P - 14-5-2020 at 01:37

You need to provide more detail.
Do you know or suspect what the impurity is?
How did you make the calcium nitrate?
What were your starting products?
What do you want to do with it, the impurity may not be a problem depending on your intended use.
Any photos?

TmNhRhMgBrSe - 14-5-2020 at 02:12

CaCO3 is from food's gas absorber.
I heat CaCO3 to remove any organic compound.
Add CaCO3 to HNO3, filter, add few drops solution to NaSCN, solution become red, add some NaOH to calcium nitrate, some white precipitate appear, filter, solution and solid also are yellow, add few drops solution to NaSCN, solution didn't change colour.
I want to make Ca(NO3)2 crystals.
I now don't have photos. Maybe later.

B(a)P - 14-5-2020 at 03:30

Was the CaCO3 and HNO3 in stoichiometric amounts?
Why add NaSCN or NaOH?
Why not just add CaCO3 in excess to HNO3, then filter.
You would then have a Ca(NO3)2 solution.

TmNhRhMgBrSe - 14-5-2020 at 04:24

I don't know how to find HNO3 concentration so didn't measure how much.
I didn't add NaSCN. The NaSCN is in another test tube. I add few drops Ca(NO3)2 solution to NaSCN. I add NaOH to remove iron.

Sulaiman - 14-5-2020 at 06:23

I think that this could be a good opportunity to practice purification by recrystalisation :P

Grow your crystals, harvest them, dissolve in distilled water and recrystalise, repeat as necessary.

start with a lot of calcium nitrate as at each recrystalisation step you need to collect only a portion of the total,
recrystalise SLOWLY to get reasonably large crystals
and do not try to crystalise out all at each step.


I have not tried myself, but activated cabon may decolourise the solution(s)

RogueRose - 14-5-2020 at 10:58

Quote: Originally posted by Sulaiman  
I think that this could be a good opportunity to practice purification by recrystalisation :P

Grow your crystals, harvest them, dissolve in distilled water and recrystalise, repeat as necessary.

start with a lot of calcium nitrate as at each recrystalisation step you need to collect only a portion of the total,
recrystalise SLOWLY to get reasonably large crystals
and do not try to crystalise out all at each step.


I have not tried myself, but activated cabon may decolourise the solution(s)


I highly recommend a little activated carbon to see if it doesn't clear things up.

Also i think Ca(NO3)2 dissolves pretty well in methanol so maybe that could be a way to purify it if the other compounds don't dissolve well in methanol.