Chemical Forums
Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: tonydoss on February 28, 2006, 11:45:34 PM
-
Hi,
can someone tell me what is the solubility of H3BO3 in 7N HNO3 or 6N HCl, or where I could find this information, please?
Thanks.
Regards,
Tony
-
I've never heard something like that. ???
However, there's a distinct possibility you are talking about the following reaction:
H3BO3 + 2H2O <-> [B(OH)4 ]- + H3O+
Orthoboric acid ionization constant (Ka) is approximately 5.37 10-10
Hence: Ka = ([B(OH)4 ]- * H+)/H3BO3
I think you can safely assume [H+] = 7N or 6N
-
I suppose you assume that all the H+ come from HNO3 or HCl.
To calculate [H3BO3] using the Ka equation I will need to know [B(OH)4- ] too, won't I? Any idea how I do that? Or I don't need, in which case... how do I do?
Thanks a lot.
Tony
-
I suppose you assume that all the H+ come from HNO3 or HCl.
Yes, I do.
On this particular occasion, I'd be tempted to use the ionization constant as a Ksp and to solve the problem as when you have to calculate solubility of a salt such as AgCl.
-
:-[ ???
Correct me if/where I'm wrong:
Ksp = 6.4x10-10 = [B(OH)4- ]x[H3O+ ] with [H3O+ ] = 7 mol/L for instance
then [B(OH)4- ] = 6.4x10-10 / 7
Ka = 5.37x10-10 = [B(OH)4- ]x[H3O+ ]/[H3BO3]
then [H3BO3] = (6.4x10-10 / 7) x 7 / 5.37x10-10
which means that [H3BO3] = Ksp/Ka = 6.4x10-10 / 5.37x10-10 = 1.19 mol/L = 73.9 mg/mL
Is that right? It seems a lot to me as generally I would be able to dissolve a few mg in 5 mL of 7N HNO3 only.
Thanks
Tony
-
Ksp = 6.4x10-10 = [B(OH)4- ]x[H3O+
Where does this Ksp come from? Could you display only the information given?
And, last but not least, what exactly do you want to know?
-
Saturated solution of boric acid in water is about 48 g/L in 20 deg C. That's about 0.77M. Such a solution has pH 4.62 - and boric acid is dissociated in 0.003% (assuming pKa1 = 9.14).
This means that dissociation of H3BO3 is meaningless - and very low pH will not change solubility of boric acid due to its dissociation.
-
I just found the Ksp somewhere on the web. I don't remember where.
I want to know how much H3BO3 crystals I can dissolve in 7N HNO3 or 6N HCl without having any excess crystals.
Following what Borek said, I guess it's 48 g/L whatever the concentration of HNO3 or HCl. Right? It seems a lot, though, as generally I can't dissolve more than a few mg in 5 mL of HNO3 solution, for instance.
-
I guess it's 48 g/L whatever the concentration of HNO3 or HCl. Right? It seems a lot, though, as generally I can't dissolve more than a few mg in 5 mL of HNO3 solution, for instance.
Perhaps thete is some other chemistry involved, although I have no idea what could it be. 4.8g H3BO3 dissolves in 100g of water at 20 deg C, this is taken from solubility tables.