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Chemistry In Our Life: Hydrolysis of Salts

ChemDy - Chemistry in our life: hydrolysis of salts


Sodium Fluoride: A Basic Salt That Protects Teeth

Sugar is a common ingredient in prepared foods. When sugar remains on your teeth, bacteria in your mouth convert it into an acid. The principal constituent of tooth enamel is a mineral called hydroxyapatite, Ca10(PO4)6(OH)2. Hydroxyapatite reacts with acids to form solvated ions and water. (Solvated ions are ions surrounded by solvent particles.) Eventually, a cavity forms in the enamel.

To help prevent acid from damaging tooth enamel, many water treatment plants add small concentrations (about 1 ppm) of salts, such as NaF,to the water. You may notice that a fluoride salt has also been added to your toothpaste. Fluoride ions displace OH− from hydroxyapatite to form fluoroapatite, Ca10(PO4)6F2, as shown in the equation below.

Ca10(PO4)6(OH)2(s) + 2F(aq) → Ca10(PO4)6F2(s) + 2OH(aq)

The fluoride ion is a much weaker base than the hydroxide ion, and fluoroapatite is therefore less reactive towards acids.


Fertilizer and Its Effect for pH of The Ground

Some of fertilizers have salt compound as the main component. There are ZA (Zwavelvuur Ammonium) or (NH4)2SO4 which contains 20.5-21% of Nitrogen and Ammonium Nitrate (NH4NO3) which contain 35% of Nitrogen. Both of them can hydrolyzed in water and decrease pH of the ground.

(NH4)2SO4(aq) → NH4+(aq) + SO42-(aq)
NH4+(aq) + H2O(l) → NH4OH(aq) + H+(aq)
NH4NO3(aq) + H2O → NH4+(aq) + NO3-(aq)
NH4+(aq) + H2O(l) → NH4OH(aq) + H+(aq)

Both of them produce H+ in water, so it can decreases pH of the ground.


Soap: Cleansing Agent In Our Life

In chemistry, soap is a salt of a fatty acid. Consumers mainly use soaps as surfactants for washing, bathing, and cleaning, but they are also used in textile spinning and are important components of lubricants.

Soaps for cleansing are obtained by treating vegetable or animal oils and fats with a strongly alkaline solution. Fats and oils are composed of triglycerides; three molecules of fatty acids attach to a single molecule of glycerol. The alkaline solution, which is often called lye (although the term "lye soap" refers almost exclusively to soaps made with sodium hydroxide), brings about a chemical reaction known as saponification.

In this reaction, the triglyceride fats first hydrolyze into free fatty acids, and then these combine with the alkali to form crude soap: an amalgam of various soap salts, excess fat or alkali, water, and liberated glycerol (glycerin). The glycerin, a useful by-product, can remain in the soap product as a softening agent, or be isolated for other uses.


Anonymous. 2000. Chemistry 12. Whitby: McGraw-Hill Ryerson.

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