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Position of Oxygen and Sulphur in the Periodic Table |
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1. Oxygen is the first member of the group VIA and sulphur is the second member of the group VIA.
2. Other member of this group are selenium, tellurium and polonium. |
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Discovery of Oxygen |
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Two scientists, Carl Scheele of Sweden and Joseph Priestly of England working independently, discovered oxygen. They published their discovery in 1777. Scheele obtained oxygen by heating potassium nitrate and mercuric oxide and called it "Fire Air". Priestley called it "Dephlogisticated Air". |
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Sources of Oxygen |
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Oxygen is the most abundant of all elements in the crust of the earth. It is present in sand and rocks in the form of silicon dioxide, and in most of the common compounds like oxides, carbonates, nitrates, etc. It is also present in air, water and land as organic compounds like carbohydrates, proteins, etc. |
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Preparation of Oxygen - From Air |
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Air, free from moisture and carbon dioxide, is bubbled through boiling mercury. The oxygen of the air combines with the mercury to form mercuric oxide, which is a red solid. |
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Preparation of Oxygen - Form Oxides |
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"Generally oxides, do not decompose when heated."
However, oxides of mercury and silver decompose completely, to yield the respective metal and oxygen.
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Preparation of Oxygen - From Nitrates |
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Metallic nitrates, when heated, give out oxygen. At the same time, most of them also give out a reddish brown gas - nitrogen dioxide, NO2. Thus, these nitrates cannot be used to prepare oxygen. However, sodium and potassium nitrates do not produce nitrogen dioxide. When these two nitrates are heated, they first melt and then readily decompose to yield oxygen. |
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Preparation of Oxygen - From Potassium Chlorate |
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When Potassium chlorate is heated strongly it decomposes to give oxygen. But if a catalyst like manganese dioxide is mixed with it, oxygen is liberated at much lower temperature, in much shorter time. Potassium chlorate and manganese dioxide are mixed in the proportion of 3:1 by mass and the mixture is heated to liberate oxygen.
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Preparation of Oxygen - From Sodium Peroxide |
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When water is added to sodium peroxide, the two react to form sodium hydroxide and oxygen.
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Preparation of Oxygen - From Potassium Permanganate |
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Potassium permanganate when heated, decomposes to form potassium manganate, manganese dioxide and oxygen. |
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Laboratory Preparation of Oxygen |
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Any of the above mentioned methods could be used to prepare oxygen in the laboratory. Mercuric and silver oxides are not used for the preparation of oxygen, as they are very expensive. |
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Physical Properties of Oxygen |
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Color-odor-Taste : Oxygen is colorless, odorless and a tasteless gas. |
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Chemical Properties of Oxygen |
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Neutral character
Oxygen is neither acidic nor basic. Both blue and red litmus are unaffected by oxygen. |
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Chemical Properties of Oxygen - With Non-Metals |
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With hydrogen
Hydrogen burns in oxygen to form water vapor.
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Chemical Properties of Oxygen - With Metals |
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With sodium
Introduce a small piece of sodium metal into a jar of oxygen. It combines with oxygen to form sodium peroxide. Allow a piece of sodium to burn in a deflagrating spoon, and then introduce it into another jar of oxygen. It burns with a brilliant yellow flame to form sodium peroxide. Add some water into both the jars. Test these solutions with red litmus. It turns blue showing the formation of a basic oxide.
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Tests for Oxygen |
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1. Oxygen is a colorless, odorless and tasteless gas.
2. It is neutral to litmus.
3. It rekindles a glowing splinter. |
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Uses of Oxygen |
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For respiration
All air breathing animals and plants use oxygen present in air by the process of respiration. This is known as aerobic respiration. During respiration, food is burnt in living cells by using oxygen to release energy for all metabolic activities. Without breathing in of air (and the oxygen it contains), life would cease to exist. |
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Rusting of Iron |
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Who has not seen the damaging effects of rusting of iron! During the process of rusting the oxide that forms is brittle and chips off from the surface. This exposes yet another layer below to the deleterious effects of moisture and air. Thus, rusting destroys the metal layer by layer and can prove to be disastrous. From early days people have tried to find methods to prevent rusting and save iron metal. |
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Conditions for Rusting of Iron |
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* The presence of water and oxygen is essential for the rusting of iron.
* Impurities in the iron, the presence of water vapor, acids, salts and carbon dioxide hastens rusting. |
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Prevention of Rusting |
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Rusting can be prevented, by applying a protective coating on the surface of the iron, so that the iron does not come in contact with air and moisture simultaneously. This coating can be of two types: (i) Non-metallic coating (ii) Metallic coating. |
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Discovery of Sulphur |
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Sulphur has been known from ancient times. The ancient Indians, the Inca Indians, Greeks and Romans used sulphur, as a fumigant, and in certain medicines. The word "Sulphur" is probably derived from the Sanskrit word "Sulveri" meaning "enemy of copper" as copper loses all its properties when heated with sulphur. It has been mentioned in the Bible on many occasions, as "Brimstone". |
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Occurrence |
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In the free state, sulphur is found in areas that have had volcanic activities. It is mostly found in Sicily in Italy and in Texas and Louisiana in the USA. To a lesser extent it is found in Russia, Canada, Japan and Poland. |
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Extraction of Sulphur |
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Large deposits of natural sulphur are found is Sicily and Louisiana. It is extracted by two processes. (i) Sicilian process (ii) Frasch process. |
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Allotropes of Sulphur |
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Rhombic sulphur is prepared by dissolving roll sulphur in carbon disulphide, and then evaporating the solution slowly, at room temperature. Eight sided crystals of rhombic sulphur crystallise out. |
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Comparison of the Properties of the Allotropes of Sulphur |
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Action of Heat on Sulphur |
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Sulphur can melt at two different temperatures.
a) If heated rapidly, it melts at 112.8oC.
b) But if heated slowly it will melt only at 118.6oC. |
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Physical Properties of Sulphur |
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Melting point
When heated rapidly sulphur melts at 112.8oC, and if heated slowly, it melts at 118.6oC. |
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Chemical Properties of Sulphur - With Air or Oxygen |
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When heated in air or oxygen, sulphur first melts and then burns with a blue flame to form sulphur dioxide and some traces of sulphur trioxide. |
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Chemical Properties of Sulphur - With Non-metals |
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With hydrogen
When hydrogen is passed through boiling sulphur, both hydrogen and sulphur combine to form hydrogen sulphide.
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Chemical Properties of Sulphur - With Metals |
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With most of the metals the reaction of sulphur is highly exothermic. Sulphur combines with metals under varying conditions of temperature to form the respective sulphides. |
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Chemical Properties of Sulphur - With Acids |
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Sulphur does not react with hydrochloric acid. Dilute sulphuric acid and dilute nitric acid also do not affect sulphur. |
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Chemical Properties of Sulphur - With Oxidising Agents |
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When sulphur is mixed with potassium nitrate, potassium chlorate etc., it forms an explosive mixture. When struck or heated or ignited, the mixture explodes e.g. gun powder.
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Uses of Sulphur |
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In agriculture
Microfined sulphur, and derivatives of sulphur are sprayed on plants and trees to destroy the fungus, insects, bacteria etc. that attack them. |
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Summary |
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Oxygen and sulphur belong to group VI A. Oxygen shows a valency of -2, while sulphur shows a valency of -2, +4 and +6. |
