The authoritative public forum
  for Metal Finishing since 1989
-----

Chemistry math for cleaning die cast zinc parts

I bought some caustic soda ⇦liquid caustic soda in bulk on Amazon [affil link] (sodium hydroxide" solution in 2001. I used it all. I paid $50 a gallon.I have since researched the stuff to find it at a much cheaper price. "sodium hydroxide" is also known as lye. 99% pure is $9 for 2 lbs. of crystals, water is free. This is my question. The MSDS says "sodium hydroxide 25% by weight" If I were mixing up a gallon of solution, am I right in assuming I weigh 1 quart of water and add that weight in crystals?

Charles Hallam
hobbyist - Wills Point, Texas, USA
July 27, 2008

Hi, Charles. Which MSDS are you talking about? The MSDS for the caustic solution you bought in 2001?

Water is more or less 2 pounds per quart (a fluid ounce of water is actually 1.043 ounce avoirdupois). But, yes, you would add 25 parts by weight NaOH to 75 parts by weight of water. But there are reasons that people buy 25 percent liquid caustic ⇦liquid caustic soda in bulk on Amazon [affil link] , and one of them is that dry caustic is a dangerous product to mix up because the heat of liberation can generate pockets of steam and blow concentrated caustic soda onto people.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 29, 2008