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CHEMISTRY | GENERAL AWARENESS
ACID, BASE AND SALTS: CHEMISTRY | GENERAL AWARENESS
1. Acid: CHEMISTRY | GENERAL AWARENESS
• An acid is a compound, which on dissolving in water yields hydronium ions (H3O+) as the only positive ions.
• The characteristic property of an acid is due to the presence of these hydronium ions.
• Acids are compounds that contain Hydrogen (Hydrochloric, HCl; Sulphuric, H2SO4; Nitric, HNO3).
• However, not all compounds that contain Hydrogen are acids (Water, H2O; Methane, CH4). Acids are usually compounds of non-metals with Hydrogen and sometimes Oxygen.
• The strength of an acid depends on the concentration of the hydronium ions present in a solution.
• However, some acids do not dissociate to any appreciable extent in water such as carbonic acid. Therefore, these acids will have a low concentration of hydronium ions.
• Strong Acid: Examples of strong acids are: hydrochloric acid,sulphuric acid, nitric acid etc.
• Weak Acid: Examples are: acetic acid, formic acid, carbonic acid etc.
• Acids are generally sour in taste. Special type of substances are used to test whether a substance is acidic or basic. These substances are known as indicators. Turmeric, litmus, china rose petals (Gudhal), etc., are some of the naturally occurring indicators.
• The most commonly used natural indicator is litmus. It is extracted from lichens . It has a mauve (purple) colour in distilled water. When added to an acidic solution, it turns red and when added to a basic solution, it turns blue. It is available in the form of a solution, or in the form of strips of paper, known as litmus paper. Generally, it is available as red and blue litmus paper.
• The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. These substances are neither acidic nor basic.
• Acids are corrosive and can burn flesh and dissolve metal.
2. Bases and Alkalis: CHEMISTRY | GENERAL AWARENESS
• A Base is a substance that gives OH-ions when dissolved in water. Bases are usually metal hydroxides (MOH). Examples include Sodium Hydroxide, NaOH, Calcium Hydroxide, Ca(OH)2. The solution of a base in water is called an alkali.
• The acidic property of an acid is due to the presence of hydrogen ions (H+) while that of a base or alkali, is due to the presence of hydroxyl (OH–) ions in them.
• The strength of a base depends on the concentration of the hydroxyl ions when it is dissolved in water.
Examples: Sodium hydroxide: NaOH, Potassium hydroxide: KOH,
Calcium hydroxide: Ca(OH)2.
Examples: Magnesium hydroxide: Mg(OH)2, Ammonium hydroxide: NH4OH.
• Bases are bitter to taste. They are soapy and slippery to touch. Sodium hydroxide and potassium hydroxide are commonly called caustic soda and caustic potash respectively.
3. pH: CHEMISTRY | GENERAL AWARENESS
• A scale for measuring hydrogen ion concentration in a solution, called pH scale has been developed. On the pH scale we can measure pH from 0 (very acidic) to 14 (very alkaline). Higher the hydronium ion concentration, lower is the pH value. The pH of a neutral solution is 7. Values less than 7 on the pH scale represent an acidic solution. As the pH value increases from 7 to 14, it represents an increase in OH–ion concentration in the solution, that is, increase in the strength of alkali.
4. Salts: CHEMISTRY | GENERAL AWARENESS
• Important salts used in everyday life and industrial applications are Sodium chloride (NaCl), Sodium carbonate, (Na2CO3), Sodium Bicarbonate, (NaHCO3), Sodium Hydroxide (NaOH)
SOME COMMON ELEMENTS & COMPOUNDS: CHEMISTRY | GENERAL AWARENESS
1. Hydrogen: CHEMISTRY | GENERAL AWARENESS
• The isotopes of hydrogen: Protium has an atomic number 1, and mass number 1, Deuterium, has an atomic number 1, and mass number 2 and Tritium has an atomic number 1, and mass number 3.
2. Carbon: CHEMISTRY | GENERAL AWARENESS
The three states of carbon are diamond, amorphous, and graphite.
• Carbon exhibits allotropy and shows maximum catenation.
• Carbon occurs both in free state as diamond, coal etc. and also in the combined form as CO2.
• Diamond is one of the allotropic forms of carbon and is the purest form of natural carbon. It is the hardest natural substance.
• Graphite is also an allotropic form of carbon, which is very soft and slippery.
• Apart from diamond and graphite, which are crystalline forms of carbon, all other forms of carbon are amorphous allotropes of carbon. Destructive distillation of coal gives products like coal gas, gas carbon, coal tar and ammonical liquor.
• Lamp Black is also known as Soot.
3. Nitrogen: CHEMISTRY | GENERAL AWARENESS
• Nitrogen is a neutral gas and is neither combustible nor a supporter of combustion.
4. Oxygen: CHEMISTRY | GENERAL AWARENESS
• There are electrons in an oxygen atom. Oxygen is noncombustible but a good supporter of combustion.
5. Chlorine: CHEMISTRY | GENERAL AWARENESS
Members of group VII A. are called halogens which means ‘salt producers’. Chlorine is prepared by the oxidation of concentrated hydrochloric acid using oxidising agents. Chlorine is a non-combustible gas but supports the burning of certain metals and nonmetals. Chlorine is highly reactive. It reacts with hydrogen, other non-metals and metals to form the corresponding chlorides. Chlorine being an acidic gas turns moist blue litmus paper to red and then bleaches it.
6. Water (H2O): CHEMISTRY | GENERAL AWARENESS
• Water is called the “Universal Solvent”.
• Metals such as gold, silver, copper, tin, etc. do not react with water. Ordinary iron gets rusted and aluminium gets tarnished. Temporary hardness and permanent hardness are the two types of hardness occurring in hard water: Water is said to be temporarily hard when it contains bicarbonates of calcium and magnesium (or hydrogen carbonates). This type of hardness can be easily removed by boiling. Water is said to be permanently hard when it contains sulphates and chlorides of calcium and magensium.
• Water becomes permanently hard when it passes over the rocks, which contain sulphates or chlorides of calcium and magnesium to form insoluble calcium bicarbonates or magnesium bicarbonates (or hydrogen carbonates). This hardness cannot be removed by boiling.
• Heavy water is prepared either by prolonged electrolysis or by fractional distillation of ordinary water. Heavy water (D2O) is colourless, tasteless and odourless liquid. It has all higher values for physical constants than the corresponding values of ordinary water. Fission in uranium-235 is brought by slow speed neutron.
• Heavy water is used for this purpose in nuclear reactors as moderators.
7. Hydrochloric Acid (HCL): CHEMISTRY | GENERAL AWARENESS
• Hydrochloric acid is prepared by dissolving hydrogen chloride gas in water.
1. It turns litmus paper from blue to red.
2. It turns methyl orange from yellow to pink.
3. It reacts with metals to form their respective chlorides and liberates hydrogen.
4. It reacts with bases to form their respective chlorides and water.
6. Hydrochloric acid is used in the production of dyes, drugs, paints, photographic chemicals and in the preparation of aqua-regia for dissolving metals like gold and platinum.
8. Nitric Acid (HNO3): CHEMISTRY | GENERAL AWARENESS
It is manufactured by the Ostwald’s Process by the reaction of ammonia and air in presence of platinum as catalyst.
• Nitric acid is colourless in pure form. Commercial nitric acid is yellowish due to the presence of dissolved nitrogen dioxide.
• Nitric acid is a strong monobasic acid. It ionizes in water readily.
• Nitric acid is a strong oxidizing agent. When it undergoes thermal decomposition, it yields nascent oxygen.
…to be continued
CONCLUSION: CHEMISTRY | GENERAL AWARENESS
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