What is function for phosphoric acid?

Answer 1

HEALTH: In living beings, phosphosrus is found in bones, teeth, nucleic acids (DNA and RNA), in the energy carriers (such as ATP), lipids, proteins and enzymes. This shows the importance of phosphorus to the health of body in general and bones and teeth in particular.

FIRE STARTER: Since phosphorus catches fire readily, it is used in all matches; earlier white phosphorus was used and in today's "safety matches" red phosphorus is used. The red phosphorus is safe because it is less volatile and less poisonous (0.1 g of white phosphorus can kill a person!) and eliminates the accidental fire as it catches fire much less readily.

FIRE STOPPER: One interesting irony is that phosphorus used to make fires (in its elemental form) is used to stop or reduce the hazards of fire (in the form of chemicals derived from it). Phosphorus compounds are among the best flame-retardants for many flammable materials; many are used as plasticizers and flame-retardants as two-in-one. Since more and more materials are made of synthetic polymers (which are mostly easily combustible) and our life is very closely associated with fire (or electricity which can give heat or fire), the use and need of fire-resistant materials is very high. In the synthetic polymers, paints and protective coatings for wood, the plasticizer/flame-retardant (& fire-resistance) phosphorus compounds are very useful. The phosphorus compounds used for this purpose (additives) can be small molecules or polymer themselves.

LUBRICANTS: High temperature lubricants are many times organo phosphates with good lubrication, thermal stablility and fire-resistant properties.

SURFACTANTS, CLEANERS: This use is being reduced at very high rate.

METAL TREATING: Phosphate coatings provide an inert and insoluble coating to many metals such as manganese, iron and zinc. The process is called phosphatizing. Also phosphoric acid is used in metal surface cleaning (for electroplating or painting). In ELECTROLESS PLATING, white phosphorus or hypophosphite is used as a reducing agent to deposit the desired metal on any surface, including non-conducting polymer objects. In ELECTROPLATING of copper or zinc, their pyrophosphate can be used as electrolyte (along with potassium pyrophosphate).

WATER TREATMENT: Many soluble phosphates are used to remove unwanted metal salts from the water (for many uses); to convert hard water to soft water by removing the metal ions as insoluble metal phosphates. For much better performance some organophosphates are used, even though they are much costlier than the normal inorganic phosphates.

FERTILIZER: The world is now supporting an unprecedented number of people and if it was not for todays science, huge number of people would have starved to death. Starvation could have been the number one cause of death as the population has crossed the level Earth can support naturally. Still starvation is very less thanks only to the Scientists, who apart from fighting diseases and being the cause for the population explosion, increased the food productivity of the world much more; not by deforestation! but by understaning and identifying plants' needs and enemies. (Also there is hybridization and now genetic engineering). The plants' needs are taken care of by Fertilizers (and micronutrients) and their enemies are fought with insecticides, fungicides, herbicides etc. on the behalf of the plants we need. It can be compared to the natural process called SYMBIOSIS where two unrelated species live together for mutual benefit. Though now so much concern is there about fertilizers, pesticides, and all, it looks like we ignore all the benefits we are getting from them. A balanced analysis of their benefit and risk is rare.
Phosphorus is one of the most important elements for the plants. Superphosphate was the most widely used phosphorus fertilizer and DiAmmomiumPhosphate is the best fertilizer as it contains both nitrogen and phosphorus in soluble form. However, the higher solubility is a cause for concern; it will be readily washed away by rain and contaminate all water sources. Unlike pesticides, fertilizers can not be substituted with other elements. Even if all other uses can be replaced with something else, the fertilizer use can not be eliminated as it is nature's choice. But different forms of phosphorus or different techniques can be used to reduce the risks.

PESTICIDES: Phosphorus pesticides have played a vital role in helping us as described above. However, now lot of concern is expressed about these pesticides. From the starting of non-specific poisons, we have learnt to make more selective poisons and still trying to improve. The pesticides can continue to do so in ever better manner.

DAILY USES: Phosphorus compounds can be found in tooth pastes (cavity protection or tartar control), in shampoos (Head&Shoulder) and many more commonly used items.

Answer 2

non-volatile, rather viscous, syrupy liquids, but still pourable. Phosphoric acid is very commonly used as an aqueous solution of 85% phosphoric acid or H3PO4.