Sciencemadness Discussion Board

Potassium Free Sawdust?

sainandrew92 - 20-10-2012 at 08:16

Hello all,

I will be performing an analytical experiment where I will measure the amount of Potassium in banana skins.

I was intriuged by the following post and decided to try it out.
I have a very rough idea as to what I am doing, but I have never done it before.

My initial plan is to just to dry the bananas out using a laboratory oven and then just burn the banana skins to get Potassium Carbonate.
However, as I do not know how well dry banana skins burn. My second idea is to mix mushed banana skins with sawdust and then carry out the above.

So... my question. I don't want the sawdust to affect my end result, and was therefore wondering if there was any sort of sawdust that had no potassium in it? Or could someone suggest an alternative material?

[Edited on 20-10-2012 by sainandrew92]

Vargouille - 20-10-2012 at 08:57

I feel like I've seen this before.

In the video, Chaney shows a brickette made of just banana skins, and the main problem with it is just that it isn't very regular in shape. You might want to try his procedure, or a simplified version, without the large machinery and the sawdust, and see how it does.

unionised - 20-10-2012 at 09:14

You could wash a lot of the potassium out of sawdust with water.

ElectroWin - 20-10-2012 at 09:28

dont use sawdust.

you should have no trouble burning the dried banana skins.
if you do, you can just pyrolyze them to charcoal. then they will burn, quite nicely.

sainandrew92 - 20-10-2012 at 09:49

Quote: Originally posted by Vargouille  
I feel like I've seen this before.

In the video, Chaney shows a brickette made of just banana skins, and the main problem with it is just that it isn't very regular in shape. You might want to try his procedure, or a simplified version, without the large machinery and the sawdust, and see how it does.


Yes, the video is part of the link I posted. I just wanted to know if any Potassium compounds in the sawdust would affect my overall results.

Unionised: I think I wasn't clear enough, sorry. I'm going to burn the mixture of banana peels and sawdust, so there won't be any sawdust left to wash.

ElectroWin: Thanks, I will see if we have a vacuum oven around.

Random - 20-10-2012 at 10:07

dont use sawdust it will screw with results, i am interested in the results

unionised - 20-10-2012 at 10:55

Wash the sawdust before you use it.

sainandrew92 - 20-10-2012 at 11:19

Ok, I understand now unionized, but I think I'll just leave the sawdust out of it.

The experiment will not be taking place for some time. The middle of November I think... but I'd be happy to provide the results should all go well.

bbartlog - 20-10-2012 at 13:57

Don't use sawdust. It does contain some amount of potassium, and washing it will hardly guarantee removal. Drying the banana skins thoroughly *should* work, but if you need some sort of supplementary fuel use something that doesn't contain potassium... kerosene, for example.

Siggebo - 20-10-2012 at 23:20

Actually, you can use an additive that contains your analyte. It's called standard addition and is an interesting technique, although I think you should rather follow the other posters' advice in this case.

Ozone - 21-10-2012 at 03:55

What analytical technique are you planning to use? For AA (or ICP), powder or shred the dried material, weigh it into an acid-washed beaker and reflux with concentrated nitric acid until the mixture is homogenous. This digest can be diluted, filtered and (after adjustment to knwon volume) analyzed.

Alternatively, you can carbonize the sample by heating with conc. sulfuric acid, then ignite in the furnace. I have found that "carbonated" ash is always less than "sulfated" ash. This may be due to the "volatility" of some carbonates; this becomes apparent when dealing with mg quantities (where very small differences can amount to large errors).

You could also pelletize the material (0.5-1.0 g) and ignite under 19 atm O2 in an oxygen bomb and analyze the washings.

Cheers,


O3

sainandrew92 - 21-10-2012 at 14:16

Siggebo: Could I? If Potassium is present in both analyte and additive, how could I distinguish what came from where? I am familiar with the concept, but I was only recently taught it so forgive me.

Ozone: I had planned on using a flame photometer; the accuracy is ok and it's simple to use for Potassium. Some quick research indicates that I should perhaps switch to AA though.
Will have to do some more looking into this, I have time on my side so any suggestions would be appreciated.

What would be the advantage of using Nitric acid over Hydrochloric?

Edit: (Quoting Ozone) "So, it depends on what you call a "Strong acid" in terms of aqueous solutions. Both are on the negative side of water and are dissociated (although HCl might do so faster). The concentation indicates that, all else equal, an equal mass of HNO3aq will give 1.83 times more H+ than HClaq. But--HNO3 is also oxidizing, which then would entail again re-defining "strong"."

I'll see what I can get, but I guess I shouldn't be too worried about which one I end up with.




[Edited on 22-10-2012 by sainandrew92]

Siggebo - 22-10-2012 at 07:32

The "distingushing" is sort of automatic; when you extrapolate to the intersection with the abscissa, you compensate for the matrix interferences at zero standard addition. It's difficult to explain; there are some geometrical arguments, but also you can think like in the text from this document:
Quote:
The Concentration value at which Response = 0 is the x-intercept of the regression line. Here it happens to be at
–1.7 units of added analyte. What does this mean in the context of the analysis? In order to have a total of 0
analyte causing 0 response, we would have to add –1.7 units analyte, or remove 1.7 units. Why? Because the
sample of unknown that was placed in every container has 1.7 concentration units!