Toothpastes, calcium compounds

The most recognized toothpaste ingredient is probably the class of compounds known as fluorides. Stannous fluoride was the first to be used in toothpaste because, unlike sodium fluoride, it did not lose its effectiveness when combined with the abrasive most common at the time, calcium phosphate. Later, sodium mono-fluorophosphate came into popular use because it too could be used with the common abrasives. 

The fluorine in fluoride toothpaste is in the form of a fluorine compound. One such compound is sodium monofluoride phosphate. The fluorine in the sodium monofluoride phosphate bonds with calcium in tooth enamel and forms a calcium fluoride layer that acts as a bacterial barrier. 

Calcium Calcium is an essential element for humans, especially in maintaining healthy bones and teeth. Calcium is found widely in nature, mainly combined with carbon and oxygen in calcium carbonate. This compound is the main ingredient in rocks such as limestone, chalk, and marble. Coral reefs build up from calcium carbonate exoskeletons that are created by marine animals called corals. Calcium carbonate is used in antacid tablets and as an abrasive in toothpaste. An abrasive is a hard material used to polish, smooth, or grind a softer material. Emery boards and sandpaper are examples of abrasive materials. 

Ruorine comes from the Latin wordfluere, which means to flow. The mineral fluorite, which contains fluorine and calcium, is used to lower the melting points of other minerals to make it easier to separate them from their ores. Fluorine compounds are added to toothpaste and drinking water to protect tooth enamel from decay. A compound of fluorine and carbon provides a non-stick coating for the cookware shown in Figure 7-20a. When fluorine reacts with isotopes of uranium, the gases that form are separated by differences in mass. This process is called uranium enrichment it provides the uranium-235 fuel for nuclear reactors. 

Fluorine compounds added to toothpaste and public drinking-water supplies have greatly reduced the incidence of cavities. Fluoride protects teeth in two ways. As teeth form, fluoride from food and drink is incorporated into the enamel layer. The fluoride makes the enamel stronger and more resistant to decay. Once teeth are present in the mouth, fluoride in saliva bonds to teeth and strengthens the surface enamel. This surface fluoride attracts calcium, which helps to fill in areas where decay has begun. 

To illustrate these different kinds of equations, consider the preparation of precipitated calcium carbonate, CaC03. This white, fine powdery compound is used as a paper filler to brighten and retain ink, as an antacid (as in the trade-named Turns), and as a mild abrasive in toothpastes. One way to prepare this compound is to react calcium hydroxide, Ca(OH)2, with sodium carbonate, Na2C03. Let us look at the different ways to write the equation for this reaction. 

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