What Causes Bleach to Melt Ice?

Facts

• Household bleach, the main ingredient of which is sodium hypochlorite (NAOCL), is itself a form of salt diluted in water and melts ice when sprayed or poured on frozen surfaces. The chemical composition of typical, non-chlorine bleaches intended for use in the home is 5 to 6 percent of sodium hypochlorite as its active ingredient in a combined solution with water, sodium chloride (table salt), sodium carbonate, sodium hydroxide and sodium polyacrylate. During typical household uses, 95 to 98 percent of bleach breaks down into salt and water. Household bleach is not chlorine bleach; they have very different chemical compositions.

Method

• Since household bleach is purchased in an already-diluted form, it can be poured directly from the bottle onto the area that needs to be de-iced. Because bleach can affect breathing and irritate both the skin and the eyes, precautions should be taken to protect yourself, your clothing and shoeware, and you should wear rubber gloves on your hands before treating an icy surface with bleach. You will be out of doors, and bleach should not be used in an area that is not well-ventilated.

Effects

• Using bleach to melt ice causes the ice to melt at a lower temperature (freezing point depression). This occurs because when bleach is poured on ice, the chemical reaction between the salts in the bleach and the frozen water in ice causes an exothermic (heat-producing) reaction. The exothermic reaction produces heat and melts the ice.

Warnings

• Bleach, when used according to directions, breaks down into salt water. The 1 to 2 percent of bleach that does not break down does not survive being treated by sewer or septic systems and does not contaminate ground water. But bleach is a caustic liquid and pouring it on concrete can damage the concrete's surface and cause it to flake, a condition called "spalling."