Sodium Hydroxide

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Sodium Hydroxide

Sodium hydroxide, NaOH, also known as lye and caustic soda, is an extremely caustic (corrosive and damaging to human tissue) white solid that readily dissolves in water. It melts at 605°F (318°C), boils at 2,535°F (1,390°C), has a density of 2.1 g/cm³, and is soluble in water at about 111 g per 100 ml (at 20°C). In its pure form, sodium hydroxide is manufactured in flakes, granules, and pellets. Worldwide production of sodium hydroxide occurs primarily in Asia, North America, and Europe, with Europe producing about one-fourth and Asia and North American producing about one-third each. The remaining production occurs in other parts of the world.

Sodium hydroxide is used in the manufacture of soaps, rayon, and paper, in petroleum refining, and in homes as drain cleaners and oven cleaners. Sodium hydroxide is one of the strongest bases commonly used in industry. Solutions of sodium hydroxide in water are at the upper limit (most basic) of the pH scale. Sodium hydroxide is made through the process called choralkali, which uses electrolysis (passing an electric current through an aqueous solution) of sodium chloride (table salt) to produce sodium hydroxide and chlorine gas.

Sodium hydroxide in household products

Two of the more common household products containing sodium hydroxide are drain cleaners and oven cleaners. When most pipes are clogged it is with a combination of fats and grease. Cleaners that contain sodium hydroxide (either as a solid or already dissolved in water) convert the fats to soap, which dissolves in water. In addition, when sodium hydroxide dissolves in water a great deal of heat is given off. This heat helps to melt the clog. Sodium hydroxide is very damaging to human tissue (especially eyes). If a large amount of solid drain cleaner is added to a clogged drain, the heat produced can actually boil the water, leading to a splash in the eyes of a solution caustic enough to cause blindness. Some drain cleaners also contain small pieces of aluminum metal. Aluminum reacts with sodium hydroxide in water to produce hydrogen gas. The bubbles of hydrogen gas help to agitate the mixture, helping to dislodge the clog.

Oven cleaners work by converting built up grease (fats and oils) into soap, which can then be dissolved and wiped off with a wet sponge.

KEY TERMS

Base —A solution with a pH greater than seven, having a greater concentration of hydroxide ions (OH) than hydrogen ions (H⁺)

Caustic —Damaging to human tissue.

pH scale —A scale used to measure the acidity or alkalinity (basicity) of a substance. It ranges from 0 to 14, with pHs below seven being acidic and greater than 7 being basic (or alkaline). A pH of 7 is neutral. Substances with pHs less than 2 or greater than 12 can be caustic to human tissue.

Soluble —Capable of being dissolved. Sugar is soluble in water.

Industrial uses of sodium hydroxide

Sodium hydroxide is used to neutralize acids and as a source of sodium ions for reactions that produce other sodium compounds. In the refining of petroleum, it is used to neutralize and remove acids. The reaction of cellulose with sodium hydroxide is a key step in the manufacturing of rayon and cellophane.

Sodium hydroxide is used as a catalyst for the manufacture of biodiesel (diesel fuel made partially or wholly from vegetable oils), which has become popular to use in the 2000s. The industrial production of soaps uses sodium hydroxide in the saponification process. The food industry uses sodium hydroxide to chemically wash various foods, including fruits and vegetables, along with using it to process cocoa, soft drinks, and ice cream.