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1. SOME BASIC CONCEPTS OF CHEMISTRY CLASS XI CHEMISTRY VOLUME - I JEE 1 CHAPTER SOME BASIC CONCEPTS OF CHEMISTRY 1 SESSION-1 PHYSICAL QUANTITIES AND SI UNITS, SCIENTIFIC NOTATION, SIGNIFICANT FIGURES, CHEMICAL CLASSIFICATION OF MATTER 1.1 PHYSICAL QUANTITIES AND THEIR S.I. UNITS: Chemists describe the behaviour of chemical substances on the basis of physical and chemical properties. The measurements of chemical properties involve chemical reactions, whereas the measurement of physical properties does not involve any chemical reactions. The common physical properties are mass, length, time, volumes, temperature, density, etc., among these mass, length and time are fundamental physical quantities. (1) Mass tells us about the quantity of matter. Mass is measured with the help of analytical balance. (2) The size of the object is measured in terms of length, area and volume. Length refers to one dimension, area to two dimensions and volume to three dimensions of space. (3) Time helps us to know how long it takes for a process to occur. The units of physical quantities depend on three basic units i.e., units of mass, length and time. Since three are independent units and cannot be derived from any other units, they are called fundamental units. But these three fundamental units cannot describe all the physical quantities. Thus seven basic units of measurement namely mass, length, time, temperature, electric current, luminous intensity and amount of substance are taken as basic units. All the other units can be derived from them are called derived units. The units of area, volume, force, work, density, velocity, energy, etc., are all derived units. S.I. UNITS: The S.I system has seven basic units from which all other units are derived. Physical Quantity Name of unit Symbol Length Meter m Mass Kilogram Kg Time Second S Temperature Kelvin K Electric current Ampere A Luminous intensity Candela Cd Amount of substance Mole mol PREFIXES: The SI units of some of the physical quantities are either too small or too large. To change the order of magnitude, these are expressed by using prefixes before the names of the basic units. Multiple Prefix Symbol 10-1 Deci d 101 deca da 10-2 Centi c 102 hecta h 10-3 Milli m 103 kilo k 10-6 Micro μ 106 mega M 10-9 Nano n 109 giga G 10-12 Pico p 1012 tera T 10-15 Femto f 1015 peta P 10-18 Atlo a 1018 exa E 10-21 Zepto z 1021 Zetla Z 10-24 Yocto y 1024 yotla Y Derived UNITS: The units of different physical quantities can be derived from the seven basic units. These are called derived units because these are derived from the basic units. For deriving these units, we can multiply or divide the symbols for units as if they are algebraic quantities. Example: 1) Volume = Length x Breadth x Height If units of length are m, then volume = m x m x m = m3 2) Area = Length x Breadth = m x m = m2 3) Density = Mass/Volume = Kg/m3 4) Acceleration = Velocity/Time = ms-1/s = m.s-2 5) Force = Mass x acceleration = Kg. m.s-2 6) Pressure = Force/Area = (Kg.m.s-2)/m2 = Kg.m-1. S-2 7) Energy, work = Force x distance = Kg. m.s-2 x m = Kg.m2 .s-2 = Joule 8) Electric charge = current x time = A. s = Coulomb 9) Electric potential = Energy/Charge = (Kg.m2 .s-2)/A.s = Joule. A-1.s-1 = Volt UNITS AND DIMENSIONAL ANALYSIS Convertion of Units: It is frequently necessary to convert one set of units to another in calculations. This can be done by a method called conversion factor method or also called dimensional analysis. In order to use this method, we write the units with every number and carry the units through the calculations, treating them as algebraic quantities. For interconversion of the units of time, we know that


1. SOME BASIC CONCEPTS OF CHEMISTRY CLASS XI CHEMISTRY VOLUME - I JEE 4 8. The correctly reported answer of the addition of 29.4406, 3.2 and 2.25 will have significant figures [1.2] A) Three B) Four C) Two D) Five 9. 81.4g sample of ethyl alcohol contains 0.002g of water. The amount of pure ethyl alcohol (to the proper number of significant figures) is [1.2] A) 81.398 g B) 81.40g C) 81.4g D) 81g 10. The least count of an instrument is 0.01 cm. taking all precautions, the most possible error in the measurement can be. [1.1] A) 0.005 cm B) 0.01 cm C) 0.0001 cm D) 0.1 cm 11. In which of the following numbers all zeroes are significant? [1.2] A) 0.500 B) 30.000 C) 0.00030 D) 0.0050 12. A student performs a titration with different burettes and finds titre values of 25.2 mL, 25.25 mL, and 25.0mL. The number of significant figures in the average titre value is. [1.2] A) 1 B) 2 C) 3 D) 4 13. The student of the calculation 2 568 5 8 4 168 . . . × in significant figure will be [1.2] A) 3.579 B) 3.570 C) 3.57 D) 3.6 1. The number of significant figures in 3.14 are [1.2] A) Three B) Infinite number C) Zero D) One 2. The Rydberg’s constant is 1.097373177 x 107 m-1. It can be expressed to three significant figures as [1.2] A) 1.0974 x 107 m-1 B) 1.09 x 107 m-1 C) 1.10 x 107 m-1 D) 1. 107 m-1 3. The number of significant figures in 0.0045 are [1.2] A) 2 B) 3 C) 4 D) 5 4. The actual product of 4.327 and 2.8 is 12.1156.The correctly reported answer will be [1.2] A) 12 B) 12.1 C) 12.12 D) 12.116 5. On dividing 0.46 by 15.374, the actual answer is 0.029236. The correctly reported answer will be [1.2] A) 0.02 B) 0.029 C) 0.0292 D) 0.02924 6. The correctly reported answer of the addition of 154.21, 6.142 and 23 will be [1.2] A) 183.352 B) 183.35 C) 183.4 D) 183 7. The value of Plank’s constant is 6.6261810-34Js. The number of significant figures in it is [1.2] A) 6 B) 5 C) 3 D) 34 8. The correctly reported answers of the addition of 294.406, 280.208 and 24, will be [1.2] A) 598.61 B) 599 C) 598.6 D) 598.614 9. Which one of the following statements is incorrect? [1.3] A) All elements are homogeneous B) Compounds made up of a number of elements are ho- mogeneous C) A mixture is not always heterogeneous D) Air is heterogeneous mixture 10. A mixture that can be separated by sublimation is [1.2] A) NH4 Cl + NaCl B) BaCl2 + NaCl C) HgCl2 + NaCl D) MgCl2 + NaCl 11. The number of significant figures in Avogadro’s number is [1.2] A) Four B) Two C) Three D) Can be any of these 12. Which of the following is not a mixture? [1.3] A) Gasoline B) Distilled alcohol C) LPG D) Iodized table salt SESSION-2 LAWS OF CHEMICAL COMBINATIONS 2.1 LAWS OF CHEMICAL COMBINATION 1) Law of conservation of mass: It states that “matter is neither created nor destroyed during any physical or chemical change” This law is also called the Law of indestructibility of matter. The following experiments illustrate the truth of this law. A) When matter undergoes a physical change: A piece of ice (solid water) is taken in a small conical flask. It is well corked and weighed. The flask is now heated gently to melt the ice (solid) into water (liquid). Ice Water Heat The flask is again weighed. It is found that there is no change in the Weight though a physical change has taken place. B) When matter undergoes a chemical change: The following chemical changes illustrate the law. Ex: Decomposition of Mercuric oxide: 100 g of mercuric oxide when heated in a closed tube, decomposed to produce 92.6 g of mercury and 7.4 g of oxygen gas, i.e. total mass of products = 100 g: HgO s Hg l O g 1 2 2 100 g 92.6g 7.4g Thus, during the above decomposition reaction, matter is neither gained nor lost. 2) Law of definite proportion (Law of constant proportion): If states that “Any pure compound however made contains the same elements in the fixed ratio of their weights”. Ex: Pure water contains 2 gm of hydrogen and 16 gm of oxygen i.e., the ratio of hydrogen and oxygen in pure water is 1: 8. Ex: A sample of CO2 may be prepared in the laboratory by A) heating lime stone (CaCO3 ), B) by burning coal in air, C) by the action of dilute hydrochloric acid on marble, D) by heating sodium bicarbonate. In each case, it is found that CO2 is made up of the same elements. i.e., carbon and oxygen, combined together in the same fixed ratio of 12: 32 or 3: 8 by mass.