Sodium hydroxide is the principal strong base used in the chemical industry. In bulk it is most often handled as an aqueous solution, since solutions are cheaper and easier to handle. It is used to drive for chemical reactions and also for the neutralization of acidic materials. It can be used also as a neutralizing agent in petroleum refining
Sodium hydroxide has also been used in conjunction with zinc for creation of the famous "Gold pennies" experiment. A penny is boiled in a solution of NaOH together with some granular zinc metal, the color of the penny will turn silver in about 45 seconds. The penny is then held in the flame of a burner for a few seconds and it turns golden. The reason this happens is that granular zinc dissolves in NaOH to form Zn(OH)42-. This zincate ion becomes reduced to metallic zinc on the surface of a copper penny. Zinc and copper when heated in a flame form brass.
Use in chemical analysis
In analytical chemistry, sodium hydroxide solutions are often used to measure the concentration of acids by titration. Since NaOH is not a primary standard, solutions must first be standardised by titration against a standard such as KHP. Burettes exposed to NaOH should be rinsed out immediately after use to prevent "freezing" of the stopcock.
Soap making via saponification is the most traditional chemical process using sodium hydroxide. The Arabs began producing soap in this way in the 7th century, and the same basic process is still used today.
For the manufacture of biodiesel, sodium hydroxide is used as a catalyst for the transesterification of methanol and triglycerides. This only works with anhydrous sodium hydroxide, because water and lye would turn the fat into soap which would be tainted with methanol.
It is used more often than potassium hydroxide because it costs less, and a smaller quantity is needed for the same results. Another alternative is sodium silicate.
Strong bases attack aluminium. This can be useful in etching through a resist or in converting a polished surface to a satin-like finish, but without further passivation such as anodizing or allodizing the surface may become corroded, either under normal use or in severe atmospheric conditions.
Food uses of lye include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel color production, poultry scalding, soft drink processing, and thickening ice cream. Olives are often soaked in lye to soften them, while pretzels and German lye rolls are glazed with a lye solution before baking to make them crisp.
Specific foods processed with lye include:
The Scandinavian delicacy known as lutefisk (from lutfisk, "lye fish").
Hominy is dried maize (corn) kernels reconstituted by soaking in lye-water. These expand considerably in size and may be further processed by cooking in hot oil and salting to form corn nuts. Nixtamal is similar, but uses calcium hydroxide instead of sodium hydroxide.
Hominy is also known in some areas of the Southeastern United States, as the breakfast food grits, dried and ground into a coarse powder. They are prepared by boiling in water, with the addition of butter and other ingredient to suit the tastes of the preparer.
Sodium hydroxide is also the chemical that causes gelling of egg whites in the production of Century eggs.
German pretzels are poached in a boiling sodium hydroxide solution before baking, which contributes to their unique crust.
Sodium hydroxide is used in the home as an agent for unblocking drains, provided as a dry crystal (e.g. "Drāno") or as a thick liquid gel. The chemical mechanism employed is the conversion of grease to a form of soap, and so forming a water soluble form to be dissolved by flushing; also decomposing complex molecules such as the protein of hair. Such drain cleaners (and their acidic versions) are highly caustic and should be handled with care.
This is a process that was used with farm animals at one time. This process involves the placing of a carcass into a sealed chamber, which then puts the carcass in a mixture of lye and water, which breaks chemical bonds keeping the body intact. This eventually turns the body into a coffee-like liquid, and the only solid remains are bone hulls, which could be crushed between one's fingertips. It is also of note that sodium hydroxide is frequently used in the process of decomposing roadkill dumped in landfills by animal disposal contractors.
In this framework, sodium hydroxide has also been used by criminals and serial killers to dispose of their victim's bodies.
Because it is a key ingredient in the process of making Methamphetamine, it is now impossible to purchase pure Sodium hydroxide as a consumer product in the United States. Products containing pure Sodium hydroxide, such as Red Devil, are no longer available for sale. As a result, amateur soapmakers must now purchase Sodium hydroxide in bulk.
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