How to make Rochelle Salt (Potassium Sodium Tartrate)

Rochelle Salt (Potassium Sodium Tartrate) a crystalline solid having a large piezoelectric effect (electric charge induced on its surfaces by mechanical deformation due to pressure, twisting, or bending), making it useful in sensitive acoustical and vibrational devices. In 1824, Sir David Brewster demonstrated piezoelectric effects using Rochelle salts, which led to him naming the effect pyroelectricity.

Materials + Methods:

Materials + Methods that I used:

• 2 50ml beakers
• alcohol lamp and stand
• Glass stir rod
• Funnel
• Filter paper or coffee filter
• 5 g Potassium bitartrate (also known as cream of tartar)
• Sodium carbonate (also known as washing soda)

1. Fill the 50 ml beaker 5 ml with water. Add 5 grams of potassium bitartrate one at a time, and stir.
2. Using the alcohol lamp, heat just until it boils, stirring constantly.
3. Remove the beaker from heat and turn off the lamp.
4. Add heaping scoops of sodium carbonate, stirring in between. The solution will fizz. Repeat until no more bubbles form upon addition of sodium carbonate and the solution is clear.
5. With a hot pad and an adult’s help, pour the hot solution into the 250 ml beaker. Use a filter-paper-lined funnel. This step takes some time. If the solution begins to cool and crystals form and clog the filter paper, simply reheat the solution and pour again.
6. Place it in the refrigerator, uncovered. Within a few hours, crystalline Rochelle salt (potassium sodium tartrate) will have begun to form. Leave it overnight.
7. The next day, carefully pour off the remaining solution and use a spatula to transfer the Rochelle salt onto filter paper to dry so you can examine it.
   

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Original Method:

1. Fill the 600 ml beaker to the first line (~25 ml) with water. Add 10 heaping scoops of potassium bitartrate one at a time, and stir.
2. Using the alcohol lamp, heat just until it boils, stirring constantly.
3. Use a hot pad and adult’s help to remove the beaker from heat and turn off the lamp.
4. Add heaping scoops of sodium carbonate, stirring in between. The solution will fizz. Repeat until no more bubbles form upon addition of sodium carbonate and the solution is clear.
5. With a hot pad and an adult’s help, pour the hot solution into the 250 ml beaker. Use a filter-paper-lined funnel. This step takes some time. If the solution begins to cool and crystals form and clog the filter paper, simply reheat the solution and pour again.
6. Place it in the refrigerator, uncovered. Within a few hours, crystalline Rochelle salt (potassium sodium tartrate) will have begun to form. Leave it overnight.
7. The next day, carefully pour off the remaining solution and use a spatula to transfer the Rochelle salt onto filter paper to dry so you can examine it.

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Results:

The salt white, but if you want to make the crystal, it’ll a lot harder. My solution is not water clear, I still have impurities, it also may appear a little strange since it has a higher refractive index and is light polarizing. To purify further: simply grow the crystals again with another salt solution. I agree with myself that this experiment is hard.

Sources:

Methods: https://learning-center.homesciencetools.com/article/how-to-make-rochelle-salt-science-project/

https://www.britannica.com/science/Rochelle-salt

https://en.wikipedia.org/wiki/Potassium_sodium_tartrate

https://mistralhowto.wordpress.com/tag/uses-for-rochelle-salt/

Methods: http://www.instructables.com/id/Make-Rochelle-Salt/