Chemistry (Part-VII) (Railway)

If a substance gains oxygen during a reaction, it is being oxidized. If it loses oxygen, it is being reduced.

• Oxidation and Reduction always take place together, so that if one substance is oxidized, another is reduced.

• If a substance gains oxygen during a reaction, it is being oxidized. If it loses oxygen, it is being reduced.

Magnesium (Mg) with atomic number of 12 has three shells (K, L, and M) with 2 valence electrons.

• It has two valence electrons in its N (outermost) shell, the inner ones being completely filled, that is with 2 (in K) and 8 (in L) electrons respectively.

It is also known as calcium sulphate Hemihydrate.

• Gypsum is a sulfate mineral composed of calcium sulfate dihydrate and has the chemical formula CaSO₄·½H₂O.

• It is heated to about 150°C to produce Plaster of Paris.

• Modern periodic table is based on atomic number. Thus, the properties of elements are related to their atomic number or electronic configuration.

• Elements are arranged according to increasing order of atomic number.

• Henry Moseley, also known as the Father of the modern periodic table.

Lead Nitrate Pb(NO₃)₂ reacts with Potassium Iodide (KI) to form Lead Iodide (PbI₂) and Potassium Nitrate (KNO₃).

• This is a double displacement reaction.

• The Lead Iodide is precipitated, and Potassium Nitrate remains dissolved in the solution.

• Pb(NO₃)₂ (aq) + 2KI (aq) → PbI₂ (s) + 2KNO₃ (aq)

The pigment that helps in carrying oxygen from the lungs to all parts of the body is known as respiratory pigment.

• Hemoglobin is the iron-containing respiratory pigment in humans, which is present in the red blood cells.

• It carries oxygen from lungs to tissues and also helps in the transportation of carbon dioxide, hydrogen ions back to the lungs from the tissues.

Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O

• When Copper is heated with concentrated nitric acid, copper is oxidized by concentrated nitric acid to produce Cu²⁺ ions.

• The nitric acid is reduced to form nitrogen dioxide, which is a poisonous brown gas with an irritating odor.

• The chemical reaction takes place as: Cu + 4HNO₃ → Cu(NO₃)₂ + 2NO₂ + 2H₂O ​

Nitrogen atom has five electrons in the valence shell. Thus, it requires three more electrons to attain the nearest noble gas configuration.

• Therefore, a nitrogen atom shares three electrons with another nitrogen atom.

• Hence, a triple bond is formed between two nitrogen atoms.

Na₂SO₄ (aq) + BaCl (aq) → BaSO₄ (s) + 2NaCl (aq)

• In double displacement reaction, two compounds react, and the positive ions (cation) and the negative ions (anion) of the two reactants switch places, forming two new compounds or products.

• Na₂SO₄ (aq) + BaCl (aq) → BaSO₄ (s) + 2NaCl (aq) is an example of double displacement reaction as two elements in the reactants are displacing each other.

Tellurium (Te) is a semi-metallic chemical element in the oxygen group or Group 16 [VIA] of the periodic table with an atomic number of 52.

• It is surrounded by Selenium (34) above it, Antimony (51) to its left, Iodine (53) to its right, and Polonium (84) below it.