CHEMISTRY (Part-III) (Railway)

Hydrogen Sulphide gas burns in air to give water and Sulphur dioxide. On heating, ferrous sulphate crystals lose water and anhydrous ferrous sulphate (FeSO) is formed. So their colour changes from light green to white. On further heating, anhydrous ferrous sulphate decomposes to form ferric oxide (Fe₂O), sulphur dioxide (SO₂) and sulphur trioxide (SO).

Electrolytic reduction is the method of reducing metals with the help of electrolysis. Metals that are placed high in the reactivity series are highly electropositive and they cannot be reduced by carbon as reducing agent. The oxides, hydroxide and chlorides of metals in fused state are electrically reduced by electrolytic reduction. Metals like Sodium (Na). K (Potassium), Mg (Magnesium), Ca (calcium), Aluminium (Al) are ob tained by this process.

A combination reaction, also known as synthesis, is a chemical reaction in which two or more substances combine to form a single substance under suitable conditions. Copper combines with oxygen to form Copper Oxide. 2Cu + O₂ + Heat ⇒ 2CuO is also an example of oxidation reaction since copper gets oxygen and hence is oxidised.

Diamond and graphite are both allotropes of carbon: they are both made entirely of the same element (carbon) but they differ in the way that the atoms bond with each other and arrange themselves in a structure. So, while they have similar chemical properties. their electronic configurations are different. The process of procuring metals from ores is called metallurgy and these naturally occurring compounds of metals are known as minerals.

Plaster of Paris is a quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate). which hardens when moistened and allowed to dry. It is produced by heating gypsum to about 150 °C.

CaSO₄.2H₂O + heat → CaSO₄.0.5H₂O + 1.5 H₂O (released as steam)

If in a chemical reaction a single substance decomposes to form two or more substances then it is known as a decomposition reaction. In the given case, Potassium Chlorate (KClO₃) is decomposed or broken down into Potassium Chloride (KCl) and Oxygen.

All the metals which are present above hydrogen in the reactivity series can displace hydrogen gas from dilute acids. This is because these acids are more reactive than hydrogen. Examples include zinc, calcium, magnesium etc. for example, in the reaction of zinc and dilute sulphuric acid. hydrogen is displaced.

Zn + H₂SO₄ → ZnSO₄ + H₂

According to Newlands' law of octaves when the elements are arranged in order of increasing atomic weights then every eighth element has properties similar to that of the first element. It was applicable only upto calcium, as after calcium, every eighth element does not possess properties similar to that of the first.

Acids taste sour, are corrosive to metals and become less acidic when mixed with bases. An acid will turn litmus paper red. Litmus is a vegetable dye that turns red to indicate an acid and blue to indicate a base.

Fossil fuels are hydrocarbons formed from the remains of dead plants and animals. Fossil fuels principally consist of carbon and hydrogen bonds. There are three types of fossil fuels which can all be used for energy provision: coal, oil and natural gas.