SSC CGL Previous Year Questions: Chemistry (2023-20) - 3 with solutions

Newlands' law of octaves - when elements are arranged in increasing order of their atomic masses, the properties of the eighth element are a repetition of the properties of the first element. It was found that the Law of Octaves was applicable only upto calcium, as after calcium every eighth element did not possess properties similar to that of the first.

Mendelevium (Md): It is a highly synthetic and radioactive element, named after Dimtri Mendeleev (Father of the periodic table), formed by bombarding einsteinium (99) with alpha particles. Transuranic elements are members of the actinide series beginning with neptunium (93) which are articially produced in nuclear reactors, accelerators and all have several isotopes that emit alpha rays.

Element 106. Discovery - Albert Ghiorso and named it after the Nuclear chemist Glenn T. Seaborg (1974).

Law of octaves (1864) states that every eighth element has similar properties when the elements are arranged in the increasing order of their atomic masses. Newlands compared the similarity between the elements to the octaves of music, where every eighth note is comparable to the first. This was the rst attempt at assigning an atomic number to each element.

68. Eka - aluminium now known as Gallium (Ga) having atomic number 31 and atomic mass 68u. Similarly Eka - Boron now known as Scandium (Sc), having atomic number - 21 and atomic mass - 45u. Eka silicon now known as Germanium (Ge) having atomic number 32 and atomic mass 72 u.

102 - Nobelium (No) (radioactive element): Relative Atomic Mass - 259 u, Block - f, Period - 7, Group - Actinide, Discovered by - Albert Ghiorso (1963). It is the tenth transuranic element.

Lithium. Atomic radius is the total distance from the nucleus of an atom to the outermost orbital of its electron. It increases from top to bottom in a group and decreases from left to right across a period. Thus, helium is the smallest element, and francium is the largest.

Group 9 elements - cobalt, rhodium, iridium and meitnerium.

Johann Dobereiner. Dobereiner's law of triads: When elements are arranged in order of increasing atomic masses, groups of three elements(triads), having similar chemical properties are obtained.

The number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms

Gallium is one of four metals (mercury, caesium, and rubidium) that can be liquid near room temperature. Symbol- Ga; Atomic Number- 31; Valence Electrons- 3. It was discovered by French chemist Paul-Emile Lecoq de Boisbaudran in 1875. It is used in electronic circuits, semiconductors, and light-emitting diodes (LEDs).

16. The atomic mass of oxygen is 16 and atomic number 8. Joseph Priestley discovered Oxygen. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent. Oxygen is Earth's most abundant element, and after hydrogen and helium, it is the third-most abundant element in the universe.

Lithium. The symbol Li and atomic number 3. Sodium is the eighth element after lithium.

Calomel (Hg₂Cl₂). Compounds and their popular names and uses: Carbonyl Chloride (COCl₂) - Phosgene used in making organic chemicals, dyestuffs, polycarbonate resins, and isocyanates for making polyurethane resins. Lead (Pb) - Galena is used as a source of lead in ceramic glaze. Potassium nitrate (KNO₃) - also called Saltpetre used in Fertilizers, Gunpowder, Rocket Propellants, Firecrackers, food processing.

CaO. Calcium oxide (Quicklime) Boiling point : 2850°C, Melting point : 2572°C. NaCl (sodium chloride) Boiling point : 1465°C, Melting point : 801°C. CaCl₂ (calcium chloride) Boiling point: 1935°C, Melting point : 772°C. LiCl (lithium chloride) Boiling point: 1382°C, Melting point: 605°C.

Calcium hydrogen carbonate {CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂}. The reaction proceeds at room temperature. It is used as an antacid to alleviate heartburn, acid indigestion. Apricot, gooseberry, gs and raisins are fruits rich in calcium. Calcium oxide (CaO), Calcium hydroxide {Ca(OH)₂}, Hydrochloric acid (HCl, strong acid).

Na₂O (Sodium oxide) - It is basic in nature. Neutral oxides are oxides which are neither acidic nor basic. In other words, oxides which neither react with acids nor with bases are called neutral oxides. Examples:- nitrous oxide (N₂O), nitric oxide (NO), carbon monoxide (CO).

Water. A polar molecule is a molecule containing polar bonds where the sum of all the bond's dipole moments is not zero. Examples of Polar Molecules: Water (H₂O), Ethanol (C₂H₅OH), Ammonia (NH₃), Sulphur dioxide (SO₂), Hydrogen sulphide (H₂S).

A compound is a material formed by chemically bonding two or more chemical elements. The type of bond keeping elements in a compound together may vary: covalent bonds and ionic bonds are two common types. The elements are always present in fixed ratios in any compound.

2.5% H, 39% S, 58.5% O. Sulfurous Acid (H₂SO₃) - Dihydrogen trioxosulphate or trioxo sulphuric acid. Mass - 82.07 g/mol. Percent composition = (mass of element / molecular mass) x 100. Composition of other compounds: Sulfuric acid (H₂SO₄) - 2.01 % H, 32.5 % S, 65.3 % O, Sodium carbonate (Na₂CO₃) - 43.40% Na, 11.32% C, 45.28% O.

One atomic mass unit is defined as one-twelfth of the mass of one carbon-12 atom. The relative atomic masses of all elements have been found with respect to an atom of carbon-12. Carbon Dioxide (CO₂) - The atomic mass of carbon and oxygen is 12u and 16u respectively. The ratio of carbon and oxygen in Carbon dioxide (CO₂) = {12 : (16 × 2)} = (12 : 32) = (3 : 8).

Chalk powder (CaCO₃) is a soft, white, porous sedimentary rock, a form of limestone composed of the mineral calcite.

Methane (CH₄). It has a high heat of combustion (CH₄ + 2O₂ → CO₂ + 2H₂O + heat). It is used as fuel. Biogas is formed by the decomposition of organic matter with the action of bacteria in the absence of oxygen. The major components of biogas - Methane (50-75%), Carbon dioxide (25-50%), Nitrogen (2-8%). Compressed Natural Gas (CNG) consists of about 80-90% methane. Liquied Petroleum Gas (LPG) consists of a compressed mixture of propane and butane in liquid form. Hydrogen is a clean fuel that, when consumed in a fuel cell, produces only water.

Kaolinite (Al₂Si₂O₅(OH)₄): A clay mineral. It's commonly found in soils and sedimentary rocks. Used in - Rubber, paint, paper making, and as a filler in some products. Orthoclase (KAlSi₃O₈): A common type of feldspar mineral (a group of rock-forming minerals). Magnesite (MgCO₃). Gypsum (CaSO₄·2H₂O): It is added to cement to slow down the rate of setting.