Significance of acids , bases &salts


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Significance of acids , bases &salts

  1. 1. Significance of Acids , Bases &salts
  2. 2. Acids • an acid is a chemical substance whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals (like calcium) to form salts. Aqueous solutions of acids have a pH of less than 7. A lower pH means a higher acidity, and thus a higher concentration of hydrogen ions in the solution. Chemicals or substances having the property of an acid are said to be acidic. • There are three common definitions for acids: the Brønsted-Lowry definition, and the Lewis definition. The Arrhenius definition defines acids as substances which increase the concentration of hydrogen ions (H+), or more accurately, hydronium ions (H3O+), when dissolved in water. The Brønsted-Lowry definition is an expansion: an acid is a substance which can act as a proton donor. By this 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. A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. Examples of Lewis acids include all metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride.
  3. 3. Properties of acids • A characteristic sour taste • ability to change the color of litmus paper from blue to red • react with certain metals to produce gaseous H2 • react with bases to form a salt and water.
  4. 4. Bases • In chemistry, a base is a substance that, in aqueous solution, is slippery to the touch, tastes bitter, changes the colour of indicators (e.g., turns red litmus paper blue), reacts with acids to form salts, and promotes certain chemical reactions (base catalysis). Examples of bases are the hydroxides of the alkali andalkaline earth metals (NaOH, Ca(OH)2, etc). Such substances produce hydroxide ions (OH-) in aqueous solutions, and are thus classified as Arrhenius bases. • Bases can be thought of as the chemical opposite of acids. Bases and acids are seen as opposites because the effect of an acid is to increase thehydronium(H3O+) concentration in water, whereas bases reduce this concentration. A reaction between an acid and base is called neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acids to produce a solution of water and salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution
  5. 5. Properties of bases • Bases change red litmus paper to bl ue. This is just the opposite of thech ange which acids cause in litmus pap er • Bases possess a bitter taste and feel soapy when in contact with the skin. • Bases react with acids to form salts a nd water (neutralization reaction). • This is the same type reaction as pre viously discussed under acids
  6. 6. salts • In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of related numbers of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge). These component ions can be inorganic such as chloride (Cl−), as well as organic such as acetate (C2H3O2 −) andmonatomic ions such as fluoride (F−), as well as polyatomic ions such as sulfate (SO4 2−). • There are several varieties of salts. Salts that hydrolyze to produce hydroxide ions when dissolved in water are basic salts and salts that hydrolyze to produce hydronium ions in water are acid salts. Neutral salts are those that are neither acid nor basic salts.Zwitterions contain an anionic center and a cationic center in the same molecule but are not considered to be salts. Examples include amino acids, many metabolites, peptides, and proteins.
  7. 7. Properties of salts • Ionic compounds are composed of a cation (positively charged atom) and an anion (negatively charged atom) in an orderly arrangement. The three dimensional arrangement of atoms or ions in a crystal is referred to as crystal lattice. The crystal lattices of sod • The simplest repeating unit of a crystal is known as a unit cell. Both NaCl and CsCl are classified as part of a cubic crystal system. The unit cells of NaCl and CsCl are different because their ions have different sizes. Three different ways that atoms can arrange themselves in a cubic crystal system are shown below. ium chloride and cesium chloride are shown below.
  8. 8. PH values
  9. 9. Thank you