KNO3 and K2SO4 Combined Solubility - The Planted Tank Forum
Old 05-18-2017, 01:24 AM Thread Starter
Planted Member

Join Date: Dec 2009
Posts: 168
KNO3 and K2SO4 Combined Solubility

So I understand that when you put KNO3 and K2SO4 in solution they each have their own solubility. I think that since they share a K+ ion, the total solubility for both of them in the same solution is less than the individual solubilities - but I can't seem to find a reference to figure out the theoretical amounts.

If I want to put 34g of KNO3 into 1L of DI water, how much K2SO4 could I theoretically dissolve in that same solution?
DMtankd is offline

Old 05-18-2017, 08:59 AM
Moderator

Join Date: Jan 2008
Location: Toronto
Posts: 11,712
You'll have to find the Ksp for each chemical and then calculate using common-ion effect

Anthony

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
and
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Eheim Pimp #362 - Eheim 2213 x2, Eheim 2028, Eheim 2217, Eheim surface skimmer and Eheim autofeeder.
Victor Pimp #33 - HPT272-125-350-4M
Old 05-18-2017, 11:56 AM Thread Starter
Planted Member

Join Date: Dec 2009
Posts: 168
Thank you.

So I think 34g KNO3 in 1L of water is .337M concentration of K. Adding K2SO4 would be

Ksp = [K]^2[SO4]

or
1.32 = (.337+2x)^2 * x

solving i get
x=.583

So I think that means that K2SO4 could dissolve at a concentration of .583M in to my .337M KNO3 solution. That would be ~101g of K2SO4? So up to 101g of K2SO4 can theoretically be dissolved in 1 L of DI with 34g KNO3?

The whole question is because I've mixed 34g KNO3 and 22g K2SO4 into 1 L DI water and I'm seeing some precipitate. 22g would have me at 1/5 of the theoretical limit, so wondering if my math is wrong?
DMtankd is offline

Old 05-18-2017, 03:35 PM
Planted Tank Guru

Join Date: Dec 2014
Location: Arnold
Posts: 3,690
Quote:
Originally Posted by DMtankd View Post

The whole question is because I've mixed 34g KNO3 and 22g K2SO4 into 1 L DI water and I'm seeing some precipitate. 22g would have me at 1/5 of the theoretical limit, so wondering if my math is wrong?
That 1lt should be 23020ppm of K, 20852ppm of NO3, and 4048ppm of S.
These low amounts should not show precipitate unless there is junk in the compounds used.

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Growing is not that difficult.
Maryland Guppy is offline
Old 05-19-2017, 01:16 AM Thread Starter
Planted Member

Join Date: Dec 2009
Posts: 168
There are a few grains that don't dissolve no matter what, assume that is the junk. Whatever this other precipitate is though, it dissolves quickly upon shaking the bottle, but then reappears again after a day or so.
DMtankd is offline

 Tags None

Message:
Options

## Register Now

In order to be able to post messages on the The Planted Tank Forum forums, you must first register.

User Name:
 Please enter a valid email address for yourself. Email Address:
OR

## Log-in

 User Name Password Remember Me?

 Thread Tools Show Printable Version Show Printable Version Email this Page Email this Page Display Modes Linear Mode Linear Mode Hybrid Mode Switch to Hybrid Mode Threaded Mode Switch to Threaded Mode

 Posting Rules You may post new threads You may post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

For the best viewing experience please update your browser to Google Chrome