#28: Banana Peels to Potassium Metal (Part 2)

In part one of this experiment, I collected, dried, burned, and boiled 40 banana peels to obtain potassium carbonate (K2CO3). Before attempting to isolate pure potassium, I needed to transform this chemical into a different potassium compound: potassium hydroxide (KOH). Here's how it happened:

1. To start, I created a saturated solution of calcium hydroxide (Ca(OH)2). I then filtered off any excess solute which hadn't been dissolved. 
2. Next, I added the potassium carbonate that I had obtained from banana peels. After thoroughly stirring the mixture, I let the beaker sit overnight as the following reaction took place: K2CO3 + Ca(OH)2 → CaCO3 + 2KOH. 
3. Initially, because the calcium hydroxide solution was saturated, there was no room to dissolve the potassium carbonate. However, as the reaction occurred, the newly formed potassium hydroxide became dissolved while the calcium carbonate was forced out of solution. 
4. When I returned the next morning, I found that the contents of the beaker had separated into two distinct layers. At the bottom lay a white slurry of calcium carbonate crystals—just as expected. 
5. By filtering the beaker's contents, I was able to remove the solid calcium carbonate. This left me with a solution of potassium hydroxide. 
6. The last step was to obtain the KOH's solid form. I started by boiling down the solution until there was nothing but wet crystals. I decided not to boil it dry for fear that the chemical would harden onto and/or corrode the beaker. 
7. Instead, I completed the dehydration process by placing the moist potassium hydroxide in a desiccator bag. A desiccator bag is basically an enclosed space containing a hydroscopic (water absorbing) substance. In my case, I added a larger container of sodium hydroxide. This would act as the desiccant by absorbing the water that evaporated from the potassium hydroxide. At the same time, the sealed bag kept the potassium hydroxide (also hydroscopic) from absorbing new water from the surrounding air. 
8. A few days later, I retrieved the fully dried potassium hydroxide. 

Stay tuned for part 3.

Potassium carbonate from banana peels (left) and calcium hydroxide (right).  

White calcium carbonate crystals falling out of potassium hydroxide solution. 

Solid potassium hydroxide after evaporation and desiccation.