Ind Acid and Base (Final)

ChE 310 Industrial ChemistryIndustrial Acids and Bases

Fabregar, Noel ChristianGuinhawa, Nadinne Adriene

Reyes, Marjorie

ChE 310 Industrial Chemistry

Industrial Acids and Bases

Introduction

Acids and bases can be found everywhere in the world around us. Lactic acid is found in sour milk, citric acid in citrus fruits, oxalic acid in rhubarb, malic acid in apples, and tartaric acid in wine. Baking soda, antacids, and lye all contain bases. Acids and bases are two broad classes of compounds that have a great deal of importance in both chemistry and biochemistry. In industry, acids and bases are used in various reactions. Sulfuric acid, one of the most important industrial chemicals, is used to manufacture fertilizers for agriculture, to make man-made fibers, paints and dyes, and to purify petroleum products. The base sodium hydroxide is used for the production of fabrics, paper, and cleaning agents. Bases are also used for various other purposes, including cleaning surfaces, refining oil and sugar, electroplating metals, and treating food products.

About 40 billion kilograms (or about 90 billion pounds) of sulfuric acid are manufactured in the United States each year, making it the number one chemical in the chemical industry. In addition, approximately 12 billion kilograms (about 26 billion pounds) of sodium hydroxide and 11 billion kilograms (about 25 billion pounds) of phosphoric acid are produced each year.

Acids have a sour taste, and many of the sour-tasting foods with which we are familiar are acidic. Vinegar, for example, is diluted acetic acid (normal household vinegar is a 3% solution of acetic acid), and gives salad dressings and pickled vegetables their tart tastes. While the tart taste of some acids can be a pleasant addition to many kinds of foods, bases have a bitter flavor, and therefore are not typically preferred for human consumption. However, many people have acquired tastes for caffeine and nicotine, both of which are alkaloids, a class of nitrogen-containing bases.

o Strong Acid - Sulfuric acid

Sulfuric acid, also known as oil of vitriol or hydrogen sulphate, is a colorless oily liquid. It is soluble in water with release of heat. It is corrosive to metals and tissue. It will char wood and most other organic matter on contact, but is unlikely to cause a fire. Long term exposure to low concentrations or short term exposure to high concentrations can result in adverse health effects from inhalation.

Sulfuric acid has many practical uses. It is perhaps best known as battery acid, though it is also used extensively in the production of fertilizers, particularly ammonium sulfate. Sulfuric acid also plays a role in the processing of iron and steel. Sulfuric acid is used to make detergents and polymers, and it's also a dehydrating agent that chemists use to remove water from substances during manufacturing. Finally, sulfuric acid is used in the production of nitroglycerine, which is both an explosive and a treatment for certain kinds of heart disease.

Production of Sulfuric Acid:

The process for producing sulfuric acid has four stages:a) extraction of sulfur

b) conversion of sulfur to sulfur dioxidec) conversion of sulfur dioxide to sulfur trioxided) conversion of sulfur trioxide to sulfuric acid

A) Extraction of sulfur

Easily the most important source of sulfur is its recovery from natural gas and oil. These contain sulfur compounds, both organic and hydrogen sulfide both of which must be removed before they are used as fuels or chemical feedstock.

Another important source of sulfur is as sulfur dioxide from metal refining. Many metal ores occur as sulfides and are roasted to form an oxide and sulfur dioxide, for example, in the manufacture of lead:

B) Conversion of sulfur to sulfur dioxide

If sulfur is the feedstock, it must first be converted to sulfur dioxide. Molten sulfur is sprayed into a furnace and burnt in a blast of dry air at about 1300 K. The sulfur burns with a characteristic blue flame:

As excess air is used the emerging gas contains about 10-12% sulfur dioxide and 10% oxygen, by volume. The gases are very hot and so are passed through heat exchangers (waste heat boilers). The gases are cooled to about 700 K and the water in the surrounding boiler pipes is converted into steam. In manufacturing one tonne of sulfuric acid, one tonne of high pressure steam is also produced.

C) Conversion of sulfur dioxide to sulfur trioxide (The Contact Process)

A typical plant contains one cylindrical vessel which acts as a fixed bed reactor with four separate beds of catalyst, known as a converter, heated to 700 K, through which the sulfur dioxide and air pass:

D) Conversion of sulfur trioxide to sulfuric acid

The sulfur trioxide formed from the third bed (and the small amount from the fourth bed) are now converted to sulfuric acid.

Sulfur trioxide reacts with water and the reaction can be expressed as:

However, water itself cannot be used for absorption as there is a large temperature rise, and a sulfuric acid mist is formed, which is difficult to handle. Instead, sulfuric acid of about 98% concentration is used. This is kept at this concentration by addition of water and removal of acid at that concentration.

o Strong Base - Sodium hydroxide

Caustic Soda is also known as “sodium hydroxide”. Whitish solid, highly corrosive and alkali salt, sold in pellets, flakes, and granular form, as well as in solution. It is highly soluble in water, with a lower solubility in ethanol and methanol, but is insoluble in ether and other non-polar solvents. Caustic soda, as a 50% solution, is an odorless and colorless liquid. It reacts readily with metals such as aluminum, magnesium, zinc, tin, chromium, bronze, brass, copper, and tantalum. It reacts with most animal tissue, including leather, human skin, and eyes. The compound is a strong, highly caustic metallic base that can cause severe chemical burns if it comes in contact with the skin.

Occidental Chemical Corporation or OxyChem, (leading North American manufacturer of polyvinyl chloride (PVC) resins, chlorine and caustic soda) The DOW Chemical Company and AkzoNobel Industrial Chemicals have the same process in manufacturing Caustic Soda. It is obtained on the electrolysis of brine. In the electrolytic cell, the sodium chloride solution is decomposed to chlorine at the anode and to a sodium hydroxide solution and

hydrogen at the cathode.

There are two electrolytic processes to produce caustic soda:

1. Diaphragm Cell

Using diaphragm cell technology, chlorine, caustic soda and hydrogen are produced simultaneously. Saturated brine enters the anode compartment of the cell, where chlorine gas is liberated. The function of the diaphragm is to separate the brine from the caustic solution (called cell effluent) at the cathode side, which is also where hydrogen gas is released.

2. Membrane Cell

Membrane cell technology is a relatively recent development. It differs from diaphragm cell technology in that a membrane rather than a diaphragm separates the solutions surrounding each electrode. The membrane is very selective and primarily allows the migration of sodium ions from the anode chamber to the cathode chamber. Saturated brine enters the anode compartment of the cell where chlorine gas is liberated. Since only sodium ions can pass through the membrane to the cathode (brine cannot pass through the membrane), the caustic soda (cell effluent) contains substantially less sodium chloride. No salt removal capabilities are required as in the diaphragm cell process.

Sodium hydroxide’s domestic uses are various and many. It is used in drain cleaning products, since its causticity can dissolve clogs and blockages; also decomposing complex molecules such as protein of hair. Beginning in the early 1900s, lye has been used to relax or straighten the hair of persons of African ethnicity. Among men, this treatment was often called a process. However, because of the high incidence and intensity of chemical burns, chemical relaxer manufacturers began switching to other alkaline chemicals (most commonly guanidine hydroxide) during the latter quarter of the twentieth century, although lye relaxers are still available, usually under use by professionals.

The chemical industry utilizes over 50% of the compound produced annually, with the paper industry alone using 25% of that to process wood pulp. Sodium hydroxide is also used in the Bayer process, which is used to manufacture aluminum. Lye is also used during the road construction process, as an underlying layer that absorbs moisture and keeps the oil from asphalt from impinging into groundwater.

Safety:

Sodium hydroxide in any form is dangerous if it comes into prolonged contact with the skin. Solid lye in pellet or powder form is inert, but if it gets damp it rapidly becomes corrosive, and can cause debilitating chemical

burns to the skin and permanent blindness if the vapor comes in contact with the eyes. Never use lye-based drain cleaner to open clogs in a toilet or plumbing linked to a septic tank, as the reaction between the gases in the tank and the sodium hydroxide can cause a major explosion. Always use gloves and protective eyewear with sodium hydroxide approved for home usage.

o Weak Acid - Acetic Acid

It is a colourless liquid that when undiluted is also called glacial acetic acid. Glacial acetic acid is a name for water-free (anhydrous) acetic acid. Acetic acid has a distinctive sour taste and pungent smell. Although it is classified as a weak acid, concentrated acetic acid is corrosive and can attack the skin.

Acetic acid is produced from oxidizing ethanol or destructively distilling wood, and is also known as acetate, Acetasol and vinegar acid. It is used in the manufacture of ink and dyes, of pesticides and food preservatives and of rubber and plastic. It is used as a pharmaceutical agent to treat ear infections, and it's also the main ingredient in vinegar. Acetic acid is released into the environment from industrial emissions as well as automotive emissions. However, when acetic acid is released into the air -- or evaporates after being released into water or soil -- sunlight breaks it down naturally.

Production of acetic acid:

A) Methanol carbonylation

Most acetic acid is produced by methanol carbonylation. In this process, methanol and carbon monoxide react to produce acetic acid according to the equation:

The process involves iodomethane as an intermediate, and occurs in three steps. A catalyst, metal carbonyl, is needed for the carbonylation (step 2).

1. CH3OH + HI → CH3I + H2O2. CH3I + CO → CH3COI3. CH3COI + H2O → CH3COOH + HI

Two related processes for the carbonylation of methanol: the rhodium-catalyzed Monsanto process, and the iridium-catalyzed Cativa process. The latter process is greener and more efficient and has largely supplanted the former process, often in the same production plants. Catalytic amounts of water are used in both processes, but the Cativa process requires less, so

+

the water-gas shift reaction is suppressed, and fewer by-products are formed.

By altering the process conditions, acetic anhydride may also be produced on the same plant using the rhodium catalysts.

B) Acetaldehyde oxidation

Prior to the commercialization of the Monsanto process, most acetic acid was produced by oxidation of acetaldehyde. This remains the second-most-important manufacturing method, although it is usually uncompetitive with the carbonylation of methanol.

The acetaldehyde may be produced via oxidation of butane or light naphtha, or by hydration of ethylene. When butane or light naphtha is heated with air in the presence of various metal ions, including those of manganese, cobalt, and chromium, peroxides form and then decompose to produce acetic acid according to the chemical equation:

2 C4H10 + 5 O2 → 4 CH3COOH + 2 H2O

The typical reaction is conducted at temperatures and pressures designed to be as hot as possible while still keeping the butane a liquid. Typical reaction conditions are 150 °C (302 °F) and 55 atm. Side-products may also form, including butanone, ethyl acetate, formic acid, and propionic acid. These side-products are also commercially valuable, and the reaction conditions may be altered to produce more of them where needed. However, the separation of acetic acid from these by-products adds to the cost of the process.

Under similar conditions and using similar catalysts as are used for butane oxidation, the oxygen in air to produce acetic acid can oxidize acetaldehyde.

2 CH3CHO + O2 → 2 CH3COOH

Using modern catalysts, this reaction can have an acetic acid yield greater than 95%. The major side-products are ethyl acetate, formic acid, and formaldehyde, all of which have lower boiling points than acetic acid and are readily separated by distillation.[35]

C) Ethylene oxidation

Acetaldehyde may be prepared from ethylene via the Wacker process, and then oxidised as above. In more recent times, chemical company Showa Denko, which opened an ethylene oxidation plant in Ōita, Japan, in 1997, commercialised a cheaper single-stage conversion of ethylene to acetic acid. The process is catalyzed by a palladium metal catalyst supported on a heteropoly acid such as tungstosilicic acid. It is thought to be competitive with methanol carbonylation for smaller plants depending on the local price of ethylene. The approach will be based on utilizing a novel selective photocatalytic oxidation technology for the selective oxidation of ethylene and ethane to acetic acid. Unlike traditional oxidation catalysts, the selective oxidation process will use UV light to produce acetic acid at ambient temperatures and pressure.

D) Oxidative fermentation

For most of human history, acetic acid bacteria of the genus Acetobacter have made acetic acid, in the form of vinegar. Given sufficient oxygen, these bacteria can produce vinegar from a variety of alcoholic foodstuffs. Commonly used feeds include apple cider, wine, and fermented grain, malt, rice, or potato mashes. The overall chemical reaction facilitated by these bacteria is:

C2H5OH + O2 → CH3COOH + H2O

A dilute alcohol solution inoculated with Acetobacter and kept in a warm, airy place will become vinegar over the course of a few months. Industrial vinegar-making methods accelerate this process by improving the supply of oxygen to the bacteria.

Nowadays, most vinegar is made in submerged tank culture, first described in 1949 by Otto Hromatka and Heinrich Ebner. In this method, alcohol is fermented to vinegar in a continuously stirred tank, and oxygen is supplied by bubbling air through the solution. Using modern applications of this method, vinegar of 15% acetic acid can be prepared in only 24 hours in batch process, even 20% in 60-hour fed-batch process.

E) Anaerobic fermentation

Species of anaerobic bacteria, including members of the genus Clostridium or Acetobacterium can convert sugars to acetic acid directly, without using ethanol as an intermediate. The overall chemical reaction conducted by these bacteria may be represented as:

C6H12O6 → 3 CH3COOH

These acetogenic bacteria produce acetic acid from one-carbon compounds, including methanol, carbon monoxide, or a mixture of carbon dioxide and hydrogen:

2 CO2 + 4 H2 → CH3COOH + 2 H2O

This ability of Clostridium to utilize sugars directly, or to produce acetic acid from less costly inputs, means that these bacteria could potentially produce acetic acid more efficiently than ethanol-oxidizers like Acetobacter. However, Clostridium bacteria are less acid-tolerant than Acetobacter. Even the most acid-tolerant Clostridium strains can produce vinegar of only a few per cent acetic acid, compared to Acetobacter strains that can produce vinegar of up to 20% acetic acid. At present, it remains more cost-effective to produce vinegar using Acetobacter than to produce it using Clostridium and then concentrate it. As a result, although acetogenic bacteria have been known since 1940, their industrial use remains confined to a few niche applications.

Acetic acid is a chemical reagent for the production of chemical compounds. The largest single use of acetic acid is in the production of vinyl acetate monomer, closely followed by acetic anhydride and ester production. The volume of acetic acid used in vinegar is comparatively small.

o Weak Base - Ammonia

Ammonia or azane is a compound of nitrogen and hydrogen with the formula NH3. It is a colourless gas with a characteristic pungent smell. When mixed with oxygen, it burns with a pale yellowish-green flame.

Natural occurrence:

Ammonia is found in trace quantities in the atmosphere, being produced from the putrefaction (decay process) of nitrogenous animal and vegetable matter. Ammonia and ammonium salts are also found in small quantities in rainwater, whereas ammonium chloride and ammonium sulfate are found in volcanic districts; crystals of ammonium bicarbonate have been found in Patagonian guano. The kidneys secrete ammonia to neutralize excess acid. Ammonium salts are found distributed through fertile soil and in seawater.

Ammonia is also found throughout the Solar System on Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Substances containing ammonia, or those that are similar to it, are called ammoniacal.

Ammonia and chemicals formed from ammonia have a remarkable number of real-world applications, many of which are as cleaners. It removes tarnish from metals, and grease, soap scum and stains from clothing. It will even strip stubborn wax from your floors. Ammonia is used in the manufacturing of fertilizers and latex products. Ammonia is also a bug and animal repellent that can be used to ward off moths or keep unwanted pests from your trash. You can even use it to absorb other odors. For example, if you place dishes of dilute ammonia in a freshly painted room, the ammonia will absorb the smell of the paint.

The pH scale

Sorensen was born on January 9, 1868, at Havrebjerg, Slagelse, Denmark and belonged to a peasant family. He was working at the Carlsberg Laboratory in 1909 when he studied the effect of ion concentration on proteins. He realized that the concentration of hydrogen ions was particularly important and hence he introduced the pH-scale. According to him, pH scale was a simple way of expressing it. A pH scale helps in measuring how acidic or basic a substance is. The pH scale is logarithmic. The meaning of the "p" in "pH" is unknown. Some references indicate that it stands for "power" while some others refer to the German potenz which means "power". Some others refer to the French puissance which again means "power". This meaning is based on the fact that the Carlsberg Laboratory was French-speaking. There are still others that refer to "potential". According to the Carlsberg Foundation pH stands for "power of hydrogen". The scale was later revised to the modern pH in the year 1924 and later it became apparent that electromotive force in cells depends on activity rather than concentration of hydrogen ions. Till date, the pH scale has found an indispensable place in almost every chemistry laboratory and is the most important aspect of any chemical procedure.

The pH meter

On October 1934, Arnold Beckman had registered patent application U.S. Patent No. 2,058,761 for his "acidimeter", later renamed the pH meter.

The Arthur H. Thomas Company, a nationally known scientific instrument dealer based in Philadelphia, was willing to try selling it. Although it was priced expensively at $195, roughly the starting monthly wage for a chemistry professor at that time, it was significantly cheaper than the estimated cost of building a comparable instrument from individual components, about $500. The original pH meter weighed in at nearly 7 kg, but was a substantial improvement over a benchful of delicate equipment. The earliest meter had a design glitch, in that the pH readings changed with the depth of immersion of the electrodes, but Beckman fixed the problem by sealing the glass bulb of the electrode.

Applications:

“Aqua Regia”

Aqua Regia (translates to Royal water in Latin) is a chemical substance. It is made by mixing one part nitric acid and three parts hydrochloric acid. It is one of the few substances that can dissolve gold and platinum, and other noble metals. Tantalum, iridium and a few other metals are not dissolved by it.

History:

Aqua regia was discovered around 800 AD, by the Muslim alchemist Geber, when he mixed common salt with vitriol (sulphuric acid). In the Middle Ages it was one of the ways that alchemists tried to find the philosopher's stone.

When Germany invaded Denmark in World War II, the Hungarian chemist George de Hevesy took the Nobel Prize medals of Max von Laue and James Franck to keep them safe. De Hevesy dissolved the medals, which were made of gold, into aqua regia. He did this so the Nazis would not steal them. He placed the jar that held the solution of aqua regia and gold on a shelf in his laboratory at the Niels Bohr Institute. The jar looked the same as hundreds of other jars in the laboratory. The Nazis thought that all the jars had normal chemicals in them. After the war, de Hevesy returned to the lab. He found the jar with the solution and removed the gold from it. He returned the gold to the Royal Swedish Academy of Sciences. The Nobel Foundation used the gold to make new medals for Laue and Franck.

Uses:

Aqua Regia is used in metal etching and scientific analysis. It is also used to clean certain lab machines from tiny metal particles. It is particularly used in the purification and extraction of gold and platinum.

Applications:

Aqua regia is primarily used to produce chloroauric acid, the electrolyte in the Wohlwill process. This process is used for refining highest quality (99.999%) gold. This method is preferred over the "traditional" chromic acid bath for cleaning NMR tubes, because no traces of paramagnetic chromium can remain to later spoil acquired spectra. Furthermore, chromic acid baths are discouraged because of the high

toxicity of chromium and the potential for explosions. Aqua regia is itself very corrosive and has been implicated in several explosions due to mishandling. Due to the reaction between its components resulting in its decomposition, aqua regia quickly loses its effectiveness. As such, its components should only be mixed immediately before use. While local regulations may vary, aqua regia may be disposed of by carefully neutralizing with an appropriate agent—such as sodium bicarbonate—before pouring down the sink. If there is a large amount of metal in solution with the acid, it may be preferable to carefully neutralize it, and absorb the solution with a solid material such as vermiculite before discarding it with solid waste.

“Natural Substances as Chemical Indicators”

A visual acid-base indicator is just a weak acid with differently colored acid and conjugate base forms. Flower and leaf pigments often fit this description. For example, take rose petals and crush them with alcohol; you have an acid/base indicator solution. Stew some red cabbage and pour off the juice; you have an acid/base indicator solution.

Many indicators can be extracted from plants. Here are a few 'natural' acid/base indicators.

Alizarin is an orange dye present in the root of the madder plant; it was used to dye wool in ancient Egypt, Persia, and India.

Cochineal is an acid-base indicator made from the bodies of dried female cochineal insects, found in Mexico and Central America. You'll have to grind about 70,000 insects to make one pound of dry indicator. The powder is about 10% carminic acid, which is yellow in acidic solution, and deep violet in alkaline solution.

Curcumin, or tumeric yellow, is a natural dye found in curry powder. It turns from yellow at pH 7.4 to red at pH 8.6.

Esculin is a fluorescent dye that can be extracted from the leaves and bark of the horse chestnut tree. You'll need to shine a black (ultraviolet) light on the indicator to get the full effect. Esculin changes from colorless at pH 1.5 to fluorescent blue at pH 2.

Anthocyanin is probably the most readily available acid/base indicator; it is the plant pigment that makes red cabbage purple, cornflowers blue, and poppies red. It changes color from red in acid solution to purplish to green in mildly alkaline solution to yellow in very alkaline solution. The color changes for red cabbage juice are shown to the right.

Litmus is a blue dye extracted from various species of lichens. Although these lichens grow in many parts of the world, almost all litmus is extracted and packaged in Holland. Litmus is red at pH 4.5 and blue around pH 8.3. While most litmus is used to make litmus papers, some is used as a coloring for beverages.

Logwood is a dye obtained from the heartwood of a tree that grows in Central America and the West Indies. The extract contains hematoxylin and hematein, which turn bright red in alkaline solution.

“Rust Remover”

Use white vinegar. The vinegar reacts with the rust to dissolve it off of the metal. To use, soak the metal in white vinegar for a few hours and then scrub the rusty paste off.

Try a lime and salt. Sprinkle salt over the rusted area so that it is thoroughly coated and then juice a lime over the top. Use as much juice as you can get, and allow the mixture to set for 2-3 hours before scrubbing off.

Make a paste using baking soda. Mix baking soda with water until it is thick enough to spread on the metal. Allow time for it to set and then scrub off.

Use oxalic acid. Take protective precautions with this method––use rubber gloves, goggles and protective clothing. Do not smoke or directly inhale the fumes of the acid. Mix about 25ml (a teaspoon is 5ml) of oxalic acid with 250ml of warm water. Soak the item for approximately 20 minutes or clean down the item with a cloth or brass brush. Wash fully and dry the item when rust removal is finished.

“Acetic Anhydride”

Acetic anhydride, or ethanoic anhydride, is the chemical compound with the formula (CH3CO)2O. Commonly abbreviated Ac2O, it is the simplest isolable anhydride of a carboxylic acid and is widely used as a reagent in organic synthesis. It is a colorless liquid that smells strongly of acetic acid, which is formed by its reaction with moisture in the air.

Production:

Acetic anhydride was first synthesized in 1852 by the French chemist Charles Frédéric Gerhardt (1816-1856) by heating potassium acetate with benzoyl chloride. Acetic anhydride is produced by carbonylation of methyl acetate:

CH3CO2CH3 + CO → (CH3CO)2O

The Tennessee Eastman acetic anhydride process involves the conversion of methyl acetate to methyl iodide and an acetate salt. Carbonylation of the methyl iodide in turn affords acetyl iodide, which reacts with acetate salts or acetic acid to give the product. Rhodium chloride in the presence of lithium iodide is employed as catalysts. Because acetic anhydride is not stable in water, the conversion is conducted under anhydrous conditions.

To a decreasing extent, acetic anhydride is also prepared by the reaction of ketene (ethenone) with acetic acid at 45–55 °C and low pressure (0.05–0.2 bar).

H2C=C=O + CH3COOH → (CH3CO)2O (ΔH = −63 kJ/mol)

Ketene is generated by dehydrating acetic acid at 700–750 °C in the presence of triethyl phosphate as a catalyst or (in Switzerland and the CIS) by the thermolysis of acetone at 600–700 °C in the presence of carbon disulfide as a catalyst.

CH3COOH   H2C=C=O + H2O (ΔH = +147 kJ/mol)CH3COCH3 → H2C=C=O + CH4

The route from acetic acid to acetic anhydride via ketene was developed by Wacker Chemie in 1922, when the demand for acetic anhydride increased due to the production of cellulose acetate. Due to its

low cost, acetic anhydride is purchased, not prepared, for use in research laboratories.

Applications:

As indicated by its organic chemistry, Ac2O is mainly used for acetylation’s leading to commercially significant materials. Its largest application is for the conversion of cellulose-to-cellulose acetate, which is a component of photographic film and other coated materials. Similarly it is used in the production of aspirin (acetylsalicylic acid), which is prepared by the acetylation of salicylic acid. It is also used as a wood preservative via autoclave impregnation to make a longer lasting timber. In starch industry, acetic anhydride is a common acetylation compound, used for the production of modified starches (E1414, E1420, E1422) Because of its use for the synthesis of heroin by the diacetylation of morphine, acetic anhydride is listed as a U.S. DEA List II precursor, and restricted in many other countries.

“Demineralization of Teeth”

Demineralization is a process to reduce the content of mineral substances in tissue or organism. It can lead to serious diseases such as osteoporosis or tooth decay. Demineralization" is another term for "dissolving the enamel."

Dental enamel is mineral, a "living stone." In your mouth, as in the rest of nature, acids dissolve minerals, transforming them from solid mineral molecules into mineral ions that exist only in solution. Strong stable acids do not break down easily, so very small quantities can keep on dissolving the minerals in your enamel. In the presence of these acids, millions, even billions, of calcium and other mineral ions are removed from the hydroxyapatite latticework. Eventually, the enamel loses its structural integrity.

Enamel demineralization represents a superficial dissolving of the surface enamel—the glassy outer shell — of the tooth. It is caused by a regular exposure of the tooth enamel to acids, such as those produced within accumulations of bacterial. Commonly, the white spots will darken as their roughened surface easily accumulates stains.

The acids that caused the demineralization of teeth are as follows:

Bacteria (primarily lactobacilli) that lives within dental plaque Frequent ingestion of acidic beverages (e.g. phosphoric acid is a

common ingredient in soda, sports drinks and flavored water—it's even found in diet soda)

Frequent exposure of the teeth to citrus fruits, which contain citric acid (particularly lemons)

Stomach acids (as in the eating disorder and patients with reflux disorders. Cells in the stomach produce hydrochloric acid to help digest food.)

Certain drugs (such as "meth", or methamphetamine), whether from the drug itself, poor nutrition, chronic dry mouth caused by the drug, or poor dental hygiene common in drug abusers.

Acids by oral bacteria that feed on starches and sugars in mouth, especially refines sugars, secreting acids as by-products.

“Car Batteries”

Lead-acid batteries are made up of plates of lead and separate plates of lead dioxide, which are submerged into an electrolyte solution of about 38%sulfuric acid and 62% water.This causes a chemical reaction that releases electrons, allowing them to flow through conductors to produce electricity. As the battery discharges, the acid of the electrolyte reacts with the materials of the plates, changing their surface to lead sulfate. When the battery is recharged, the chemical reaction is reversed: the lead sulfate reforms into lead dioxide and lead with the sulfate returning to the electrolyte solution restoring the electrolyte specific gravity. With the plates restored to their original condition, the process may now be repeated.

“Acidic or Basic Fertilizer”

Types

Fertilizers can be found in most garden centers that have a high proportion of acids, such as cottonseed, or a high proportion of nitrogen, or of bases, such as lime. Such fertilizers provide a convenient way to amend an undesirable soil pH. Whether soil needs to be amended to correct its prevailing pH depends on a variety of factors, including the plants to be grown.

Plant Needs

Whether to use an acid, basic, or more neutral fertilizer depends on what the plants being fed need. Some plants require a highly or slightly acidic soil to thrive; these so-called "acid-loving plants" include blueberries, azaleas, camellias, and most evergreens. In circumstances where the existing soil pH is too high, using a fertilizer that acidifies the soil is important. Other plants do best in alkaline soil. This group includes lilacs, barberry, and mock orange. Such plants may require a fertilizer rich in bases if the existing soil is too acidic. Most plants thrive in neutral soil. To accommodate most garden shrubs, annuals, and perennials, either acids or bases must be added to soil to amend an alkaline or acidic soil.

Use of Acidic or Basic Fertilizer

Use of acidic and basic fertilizers should not be indiscriminate. Initial application should be followed up with additional soil testing after a couple of weeks to see if the pH has been successfully amended. If not, more of the acidic or basic fertilizer should be applied, provided it's not an inappropriate time to fertilize, such as early fall. If the soil has the desired pH, gardeners should switch to a normal fertilizer.

“Acid-Containing or Acid-Free”

Acid-containing paper is paper that is slightly acidic, with a pH below 7. It is made of wood pulp that has a high acid content. Acid-free paper is paper that contains no acids. It is paper that has a neutral pH of 7. It is "rag" paper made from cotton fibers or buffered paper made from

wood pulp with alkaline solution. It is also lignin- and sulfur-free. The difference between acid-free and acid-containing paper is the presence of acid. If you look at the two papers, you cannot see the difference between them. You will notice it only if you keep the paper for a long period since acids cause damage.

Acid containing-paper is used for every day life because it is cheaper. There are different qualities of paper made from wood pulp, the cheapest being "newsprint" the paper used for newspapers. Paper made from wood pulp is not so strong as traditionally made papers because it is made from a mush of short fibers and does not have the long strands of (say) linen paper. Acid-free paper is used for high quality paper, photos or documents.

Advantages:

Acid-containing paper: It is easy to make and cheaper. Acid-free paper: Resistant and can be stored for 200 years.

Disadvantages:

Acid-containing paper: it rapidly breaks down owing to the action of the acid content on the fibers, which begin to rot; Paper turns yellow, brittle, smells and disintegrates; Cannot be stored for a very long time.

Acid-free paper: Costly; Hard to make