What Is Caustic Soda and Where Can You Get It?

Caustic Soda Information

Lye Soap
Caustic soda may be used to make homemade lye soap. Michael Westhoff, Getty Images

Caustic soda is one of the common names for sodium hydroxide (NaOH), which is also known as lye. Its common name derives from its chemical identity as a sodium hydrate and because it is caustic or corrosive. In pure form, caustic soda is a waxy, white solid. It readily absorbs water and forms aqueous solutions. Commercially available caustic soda or sodium hydroxide is usually sodium hydroxide monohydrate, NaOH·H2O.

Key Takeaways: Caustic Soda

  • Caustic soda is one of the common names for sodium hydroxide (NaOH).
  • It is also known as lye, although lye may refer to either potassium hydroxide or sodium hydroxide.
  • Pure caustic soda is sold for making candles or soap.
  • Impure caustic soda is found in drain cleaner.
  • Because lye is used to make illegal drugs, it's harder to buy large quantities than in the past. However, small containers are available in stores and online.

Uses of Caustic Soda or Lye

Lye is used for soap making, candle making, homemade biodiesel, frosting glass, making several foods, and for chemistry experiments.

How to Get Caustic Soda or Lye

It's much harder to get hold of lye than it used to be in the past. The main source of caustic soda was Red Devil Lye, but that product is off the market now. Why is it hard to get lye? The reason is because it can be used to control pH during methamphetamine production. There are still a few ways to get the chemical. Make sure the product is 100% sodium hydroxide, lye, or caustic soda. This is especially important if you are making food, since an impure product may contain dangerous contaminants. Sources of lye include:

  • Drain cleaner (check the label) - e.g., Roebic Crystal Drain Cleaner, sold as Lowes
  • Sodium hydroxide from an online chemical supply store
  • Soap making store
  • Candle making store
  • Biodiesel supply store

Be aware, when purchasing caustic soda or lye, you may need to sign a statement that you're not using it for illegal activities. Or, you may not need to sign anything, since a credit card pretty much provides all the details needed to find you if the authorities think you're a rising drug lord.

Helpful Tips

  • Since it's relatively hard to get hold of this chemical, you may need to buy in bulk. You may be able to find other people that need the chemical to help split the cost. It's not an expensive item, but you probably don't need several pounds of it.
  • Keep the container sealed and away from moisture. Caustic soda absorbs and reacts with water.
  • Keep lye away from children and pets. Touching or ingesting it can cause a potentially severe chemical burn.
  • Use gloves or utensils to handle caustic soda.
  • Perform reactions involving this chemical in a well-ventilated room or outdoors. The reaction releases heat and noxious fumes.

Caustic Soda or Lye Substitutes

Depending on the purpose, you may be able to substitute a chemically similar strong base, potassium hydroxide (KOH). This is a chemical you can, if you are extremely dedicated, make yourself by soaking wood ashes in water. To do this, soak a large quantity of ashes in a small amount of water. Allow about a week for the water to extract the lye. Drain the liquid, which contains potassium hydroxide, filter it, and boil it to concentrate the alkali. Be careful to use gloves when handling the liquid. The project should only be performed outdoors or in a well-ventilated space.

Sources

  • Brodale, G. E. and W. F. Giauque (1962). "The freezing point-solubility curve of aqueous sodium hydroxide in the region near the anhydrous-monohydrate eutectic." Journal of Physical Chemistry, volume 66, issue 10, pp. 2051–2051. doi:10.1021/j100816a051
  • Deming, Horace G. (1925). General Chemistry: An Elementary Survey Emphasizing Industrial Applications of Fundamental Principles (2nd ed.). New York: John Wiley & Sons, Inc.
  • Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. ISBN 1439855110.
  • O'Brien, Thomas F.; Bommaraju, Tilak V. Hine, Fumio (2005). Handbook of Chlor-Alkali Technology, vol. 1. Berlin, Germany: Springer. Chapter 2: History of the Chlor-Alkali Industry, p. 34. ISBN 9780306486241.
  • Pickering, Spencer Umfreville (1893): "LXI.—The hydrates of sodium, potassium, and lithium hydroxides." Journal of the Chemical Society, Transactions, vol. 63, pp. 890–909. doi:10.1039/CT8936300890