Test: SSC CGL Previous Year Questions: Chemistry (2023-20) - 3 - SSC CGL MCQ

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).

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.

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.

Noble gases. In the periodic table, the highly electronegative halogens (group 17) and the highly electropositive alkali metals (group 1) are separated by noble gases which are present in group 18.

Robert Boyle (Boyle’s law: For a fixed amount of an ideal gas kept at a xed temperature, pressure and volume are inversely proportional, so PV= constant). Amedeo Avogadro {Avogadro’s hypothesis (1811) states that the total number of atoms /molecules of a gas is directly proportional to the volume occupied by the gas at constant temperature and pressure}. Joseph Gay Lussac {GayLussac's law (1808) states that the pressure exerted by a gas (of a given mass and kept at a constant volume) varies directly with the absolute temperature of the gas}. John Dalton {Dalton’s law of partial pressures (1801) states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures exerted by each individual gas in the mixture}.

Sublimation - The transition of a substance directly from the solid to the gas state, without passing through the liquid state. Examples - Ammonium chloride (NH₄Cl), iodine, camphor, naphthalene, dry ice.

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.

Na (Sodium) - Group 1A (Alkali Metal). Electropositivity can be defined as the tendency of an atom to donate electrons and form positively charged cations. Most Electropositive elements: Caesium. Most electronegative element - Fluorine.

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.

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

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.