As a hobbyist, I am developing a technique to grow perfect, large and completely translucent crystals of CuSo4 5H2O . I have noticed that as my mother solution becomes depleted there is a green layer at the bottom of the otherwise blue solution. I'm curious as to what this could be. Does anyone have any ideas just offhand?

The solvent is filtered and distilled water.  The CuSO4 has been washed, dissolved, filtered and recrystallized twice before use in the mother liquid.  Growing temperature is 4 c.

The green layer is always at the bottom and becomes noticeable after about a month and is unmistakably visible after two months. 

37 minutes ago, crystalguy said:

As a hobbyist, I am developing a technique to grow perfect, large and completely translucent crystals of CuSo4 5H2O . I have noticed that as my mother solution becomes depleted there is a green layer at the bottom of the otherwise blue solution. I'm curious as to what this could be. Does anyone have any ideas just offhand?

The solvent is filtered and distilled water.  The CuSO4 has been washed, dissolved, filtered and recrystallized twice before use in the mother liquid.  Growing temperature is 4 c.

The green layer is always at the bottom and becomes noticeable after about a month and is unmistakably visible after two months. 

I don't know but my first guess would be that water may absorb CO2 from the air. You could perhaps be getting some basic copper carbonate (carbonate hydroxide). Perhaps @John Cuthber may know. 

Question is also what is the pH of the water. Normaly some Drops of H2SO4 avoid this phenomena.

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Posted 6 hours ago

7 hours ago, crystalguy said:

As a hobbyist, I am developing a technique to grow perfect, large and completely translucent crystals of CuSo4 5H2O . I have noticed that as my mother solution becomes depleted there is a green layer at the bottom of the otherwise blue solution. I'm curious as to what this could be. Does anyone have any ideas just offhand?

The solvent is filtered and distilled water.  The CuSO4 has been washed, dissolved, filtered and recrystallized twice before use in the mother liquid.  Growing temperature is 4 c.

The green layer is always at the bottom and becomes noticeable after about a month and is unmistakably visible after two months. 

Expand  

I don't know but my first guess would be that water may absorb CO2 from the air. You could perhaps be getting some basic copper carbonate (carbonate hydroxide). Perhaps @John Cuthber may know. 

Thanks for the idea, I think you may be right. I'm going to try to isolate it and test for carbonate ion.

11 hours ago, crystalguy said:

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Posted 6 hours ago

I don't know but my first guess would be that water may absorb CO2 from the air. You could perhaps be getting some basic copper carbonate (carbonate hydroxide). Perhaps @John Cuthber may know. 

Thanks for the idea, I think you may be right. I'm going to try to isolate it and test for carbonate ion.

Don't forget to pursue @chenbeier's suggestion as well. If you add a few drops of sulphuric acid you may find the green layer dissipates.

Edited May 8, 20232 yr by exchemist