ABOUT ACIDS:An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour,reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of lessthan 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red. Chemicals orsubstances having the property of an acid are said to be acidic.Common examples of acids include acetic acid (in vinegar), sulfuric acid (used in car batteries), andtartaric acid (used in baking). As these three examples show, acids can be solutions, liquids, or solids.Gases such as hydrogen chloride can be acids as well. Strong acids and some concentrated weak acidsare corrosive, but there are exceptions such as carboranes and boric acid.There are three common definitions for acids: the Arrhenius definition, the Brønsted-Lowry definition,and the Lewis definition. The Arrhenius definition states that acids are substances which increase theconcentration of hydronium ions (H3O+) in solution. The Brønsted-Lowry definition is an expansion: anacid is a substance which can act as a proton donor. Most acids encountered in everyday life areaqueous solutions, or can be dissolved in water, and these two definitions are most relevant. The reasonwhy pHs of acids is less than 7 is that the concentration of hydronium ions is greater than 10−7 molesper liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidsthus have pHs of less than 7. By the Brønsted-Lowry definition, any compound which can easily bedeprotonated can be considered an acid. Examples include alcohols and amines which contain O-H or N-H fragments.In chemistry, the Lewis definition of acidity is frequently encountered. Examples of Lewis acids includeall metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride.Hydronium ions are acids according to all three definitions. Interestingly, although alcohols and aminescan be Brønsted-Lowry acids as mentioned above, they can also function as Lewis bases due to the lonepairs of electrons on their oxygen and nitrogen atoms.USES and APPLICATIONS OF ACIDS:There are numerous uses for acids. Acids are often used to remove rust and other corrosion from metalsin a process known as pickling. They may be used as an electrolyte in a wet cell battery, such as sulfuricacid in a car battery.In the chemical industry, acids react in neutralization reactions to produce salts. For example, nitric acidreacts with ammonia to produce ammonium nitrate, a fertilizer. Additionally, carboxylic acids can beesterified with alcohols, to produce esters.Acids are used as additives to drinks and foods, as they alter their taste and serve as preservatives.Phosphoric acid, for example, is a component of cola drinks. Acetic acid is used in day to day life asvinegar. Carbonic acid is an important part of some cola drinks and soda. Citric acid is used as apreservative in sauces and pickles.
Tartaric acid is an important component of some commonly used foods like unripened mangoes andtamarind. Natural fruits and vegetables also contain acids. Citric acid is present in oranges, lemon andother citrus fruits. Oxalic acid is present in tomatoes, spinach, and especially in carambola and rhubarb;rhubarb leaves and unripe carambolas are toxic because of high concentrations of oxalic acid.Ascorbic acid (Vitamin C) is an essential vitamin required in our body and is present in such foods asAlma, lemon, citrus fruits, and guava.Certain acids are used as drugs. Acetylsalicylic acid (Aspirin) is used as a pain killer and for bringing downfevers.Acids play very important roles in the human body. The hydrochloric acid present in our stomach aids indigestion by breaking down large and complex food molecules. Amino acids are required for synthesis ofproteins required for growth and repair of our body tissues. Fatty acids are also required for growth andrepair of body tissues. Nucleic acids are important for the manufacturing of DNA, RNA and transmissionof characters to offspring through genes. Carbonic acid is important for maintenance of pH equilibriumin the body.Examples of Acids Hypochlorous acid (HClO), chlorous acid (HClO2), chloric acid (HClO3), perchloric acid (HClO4), Sulfuricacid (H2SO4), Fluorosulfuric acid (HSO3F),Nitric acid (HNO3), Phosphoric acid (H3PO4),Chromic acid(H2CrO4), Boric acid (H3BO3).A base in chemistry is a substance that can accept hydrogen ions (protons) or more generally, donateelectron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions (OH−)quantitatively. The Brønsted-Lowry theory defines bases as proton (hydrogen ion) acceptors, while themore general Lewis theory defines bases as electron pair donors, allowing other Lewis acids thanprotons to be included. The oldest Arrhenius theory defines bases as hydroxide anions, which isstrictly applicable only to alkali. In water, by altering the autoionization equilibrium, bases give solutionswith a hydrogen ion activity lower than that of pure water, i.e. a pH higher than 7.0 at standardconditions. Examples of common bases are sodium hydroxide and ammonia. Metal oxides, hydroxidesand especially alkoxides are basic, and counteranions of weak acids are weak bases.BASES:Bases can be thought of as the chemical opposite of acids. A reaction between an acid and base is calledneutralization. Bases and acids are seen as opposites because the effect of an acid is to increase thehydronium ion (H3O+) concentration in water, whereas bases reduce this concentration. Bases and acidsare typically found in aqueous solution forms. Aqueous solutions of bases react with aqueous solutionsof acids to produce water and salts in aqueous solutions in which the salts separate into theircomponent ions. If the aqueous solution is a saturated solution with respect to a given salt solute anyadditional such salt present in the solution will result in formation of a precipitate of the salt.
PROPERTIES OF BASES: Slimy or soapy feel on fingers, due to saponification of the lipids in human skin. Concentrated or strong bases are caustic on organic matter and react violently with acidic substances. Aqueous solutions or molten bases dissociate in ions and conduct electricity. Reactions with indicators: bases turn red litmus paper blue, phenolphthalein pink, keep bromothymol blue in its natural colour of blue, and turns methyl orange yellow. The pH level of a basic solution is higher than 7. Bases are bitter in taste.EXAMPLES OF BASES: Potassium hydroxide (KOH), Barium hydroxide (Ba(OH)2),Caesium hydroxide (CsOH),Sodiumhydroxide (NaOH),Strontium hydroxide (Sr(OH)2),Calcium hydroxide (Ca(OH)2),Magnesium hydroxide(Mg(OH)2),Lithium hydroxide (LiOH), Rubidium hydroxide (RbOH)SALTS:In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and abase. They are composed of cations (positively charged ions) and anions (negative ions) so that theproduct is electrically neutral (without a net charge). These component ions can be inorganic such aschloride (Cl−), as well as organic such as acetate (CH3COO−) and monatomic ions such as fluoride (F−), aswell as polyatomic ions such as sulfate (SO42−).There are several varieties of salts. Salts that hydrolyze to produce hydroxide ions when dissolved inwater are basic salts and salts that hydrolyze to produce hydronium ions in water are acid salts. Neutralsalts are those that are neither acid nor basic salts. Zwitterions contain an anionic center and a cationiccenter in the same molecule but are not considered to be salts. Examples include amino acids, manymetabolites, peptides, and proteins.Molten salts and solutions containing dissolved salts (e.g., sodium chloride in water) are calledelectrolytes, as they are able to conduct electricity. As observed in the cytoplasm of cells, in blood,urine, plant saps and mineral waters, mixtures of many different ions in solution usually do not formdefined salts after evaporation of the water. Therefore, their salt content is given for the respective ions.PropertiesPotassium dichromate, a bright orange salt used as a pigmentManganese dioxide, an opaque black saltSalts can appear to be clear and transparent (sodium chloride), opaque, and even metallic and lustrous(iron disulfide). In many cases the apparent opacity or transparency are only related to the difference insize of the individual monocrystals. Since light reflects from the grain boundaries (boundaries between
crystallites), larger crystals tend to be transparent, while polycrystalline aggregates look like whitepowders.Salts exist in many different colors, e.g., yellow (sodium chromate), orange (potassium dichromate), red (potassium ferricyanide), mauve (cobalt chloride hexahydrate), blue (copper sulfate pentahydrate, ferric hexacyanoferrate), purple (potassium permanganate), green (nickel chloride hexahydrate), white (sodium chloride), colorless (magnesium sulfate heptahydrate) and black (manganese dioxide).Most minerals and inorganic pigments as well as many synthetic organic dyes are salts. The color of thespecific salt is due to the presence of unpaired electrons in the d-orbital of transition elementsDifferent salts can elicit all five basic tastes, e.g., salty (sodium chloride), sweet (lead diacetate, whichwill cause lead poisoning if ingested), sour (potassium bitartrate), bitter (magnesium sulfate), andumami or savory (monosodium glutamate).Salts of strong acids and strong bases ("strong salts") are non-volatile and odourless, whereas salts ofeither weak acids or weak bases ("weak salts") may smell after the conjugate acid (e.g., acetates likeacetic acid (vinegar) and cyanides like hydrogen cyanide (almonds)) or the conjugate base (e.g.,ammonium salts like ammonia) of the component ions. That slow, partial decomposition is usuallyaccelerated by the presence of water, since hydrolysis is the other half of the reversible reactionequation of formation of weak salts.