[kevinkevin]

  I was making potassium nitrate and I came up with a quick and easy method for making it more pure and I was hoping to get some feed back on it if it is a good thing to do.  I make it by simply mixing solutions of potassium chloride and ammonium nitrate, and then heat the mixed solution to dissolve all of the potassium chloride.  Since potassium nitrate is insoluble at low temperatures I put it in the freezer until the solution temperature is zero degrees Celsius.  There are then large crystals of potassium nitrate that can be easily separated from the aqueous ammonium chloride.  I separate them by poring out all the leftover solution and just keep the crystals of potassium nitrate which are at the bottom of the beaker.  But since these crystals still probably have large amounts of ammonium chloride on them I put them in a beaker and then rinse them with water, reheat the solution and then freeze it again to separate the potassium nitrate.  I then repeat this process one more time and then collect the potassium nitrate for storing.  Is this a method that will yield more pure potassium nitrate?  Thanks.   

[Arkcon]

Yes, what you're doing is fractional crystallization, and its a method for purifying soluble solids.  In a lab with better facilities than your home, you could get better results.  Marie Curie isolated radium salts with pretty much the same method, and the method hasn't changed much since then.

[kevinkevin]

   Thank you very much!

[vmelkon]

There is an alternative method that is likely to give better yields but you need KOH.
Make a solution of KOH and NH4NO3.
Heat the solution and it will drive off the NH3 as a gas which you can recover if you want.

[kevinkevin]

    I like that suggestion.  I am always down for a reaction that will give a better yield, thank you for bringing it up!  Is there an easy legal way to obtain potassium hydroxide?  Thanks.

   Just wondering when it is heated to drive off the ammonia will there be anything left in the solution with the potassium nitrate or will there still be hydroxide ions? 

[kevinkevin]

  Would it be possible for me to make it using potassium chloride and sodium hydroxide?  Is there a way for me to separate the solutions after mixing to obtain the potassium hydroxide? 

[Borek]

Just wondering when it is heated to drive off the ammonia will there be anything left in the solution with the potassium nitrate or will there still be hydroxide ions? 

Depends on how accurately you will measure amounts of KOH and ammonium nitrate. But in general OH^- gets neutralized by NH₄⁺, so they are removed from the solution (you know they are ALWAYS present in water due to autodissociation, don't you?)

[Arkcon]

  Would it be possible for me to make it using potassium chloride and sodium hydroxide?  Is there a way for me to separate the solutions after mixing to obtain the potassium hydroxide? 

No, that is much harder than you initial crystallization methods, the various salts are too too soluble, and too slghtly affected by solution temperature.  And also, unlike later suggestions, non-volatile.

I like that suggestion.  I am always down for a reaction that will give a better yield, thank you for bringing it up!  Is there an easy legal way to obtain potassium hydroxide?  Thanks.

It is as easy and legal to acquire, use and have potassium hydroxide as it is to acquire, use and have potassium nitrate or ammonium nitrate.  You've already achieved the last one, so why bring it up?

Just wondering when it is heated to drive off the ammonia will there be anything left in the solution with the potassium nitrate or will there still be hydroxide ions? 

No, the hydroxide ions won't exist alone in solution.  Do you know why?  You should have that sort of basic knowledge before you start to play with energetic compounds.

[vmelkon]

Definitely, you should know some chemistry before doing anything.
I think we all know what "nitrates" are all about.

[kevinkevin]

   I talked to my chemistry teacher today about the things you guys brought up and I got some questions answered.  First I asked about autodissociation and I now have a clear understanding about that.  Then we talked about why there would be no hydroxide or ammonia ions in solution and I believe I now understand that.  It is because as the solution is heated the water and ammonia will escape as a gas making the ammonia and hydroxide ions still in solution form more water and ammonia which will escape as a gas until there is really no more ammonia or hydroxide, And what little is left will just form ammonium hydroxide right?   

[vmelkon]

   I talked to my chemistry teacher today about the things you guys brought up and I got some questions answered.  First I asked about autodissociation and I now have a clear understanding about that.  Then we talked about why there would be no hydroxide or ammonia ions in solution and I believe I now understand that.  It is because as the solution is heated the water and ammonia will escape as a gas making the ammonia and hydroxide ions still in solution form more water and ammonia which will escape as a gas until there is really no more ammonia or hydroxide, And what little is left will just form ammonium hydroxide right?   

I think you got the idea but you have the words mixed up.

"ammonia and hydroxide ions still in solution form more"
That should be ammonium and hydroxide.
ammonium = NH4+
ammonia = NH3

As for the reaction between ammonia and water, very little of it forms NH4+ and OH-. Most of it is NH3 and water and ammonia solutions always give off NH3.