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Sodium hydroxide (NaOH), also known as caustic soda or lye in North America, is a caustic metallic base used in industry (mostly as a strong chemical base) in the manufacture of paper, textiles, and detergents.
Sodium hydroxide is occasionally used in the home as an agent for unclogging stuck drains, but it is highly caustic and has a
high danger of causing chemical burns, permanent injury or scarring, and
blindness, due to its high reactivity. Therefore, it should be stored separately.
When sodium hydroxide reacts with water and fluids, it can become hot enough to cause fires. For this reason, it is important to have the proper type of chemical fire extinguisher on hand before working
with sodium hydroxide. Store this product in an airtight container to prevent NaOH from absorbing water and CO2 from the air. It can create enough heat to ignite
flammables (such as alcohols), so add slowly in biodiesel processor.
Sodium hydroxide is manufactured by electrolysis of an aqueous solution
of sodium chloride. It is a by-product of the process that is used to
make chlorine.
Both NaOH and KOH are commonly called "lye" in North America, which can lead to some
confusion. However, most commercially availalable lye is NaOH.
Lye is also a main ingredient in the making of soap. NaOH is now most commonly used for
this, but traditionally KOH was used because it was easier to obtain.
In solution, Sodium Hydroxide will leave a yellow stain on fabric and paper.
Biodiesel
For biodiesel, this is one of the main reactants, like catalyst. This only works with anhydrous sodium hydroxide, because water turns biodiesel into soap (saponification).
However, it is more used than potassium hydroxide, KOH, because it dissolves in methanol much more easily than KOH, and it doesn't
"clump".
Another alternative in the future is to use sodium silicate
instead of sodium hydroxide.
Usage in cooking
Lye is also used for preparing various foodstuffs; examples are the Norwegian
delicacy known as Lutefisk, which is basically cod jellied in lye, pretzels, and German lye rolls. Olives are
often soaked in lye.
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