JEE Main Chemistry Short Notes: Mole Concept and Stoichiometry PDF

www.gradeup.co 1  www.gradeup.co Mole concept and Stoichiometry is an important topic from JEE Main / JEE Advanced Exam Point of view. Some questions can be asked directly. Most importantly, the whole Chemistry includes this topic. Thus, it is very important to have a...

www.gradeup.co 1  www.gradeup.co Mole concept and Stoichiometry is an important topic from JEE Main / JEE Advanced Exam Point of view. Some questions can be asked directly. Most importantly, the whole Chemistry includes this topic. Thus, it is very important to have a clear cut on this topic. This short notes on Mole concept and Stoichiometry will help you in revising the topic before the JEE Main & IIT JEE Advanced Exam. You can also download Mole concept and Stoichiometry notes PDF at end of the post. 1. Properties of Matter and their Measurements Anything that possesses mass and occupies space is called matter. Classification of Matter Classification of matter on the basis of their physical and chemical properties. Physical classification: Matter is physically classified into solid, liquid and gaseous state. The order of intermolecular force of attraction among their physical state is: Solid> liquid> gas Chemical classification: Chemically, the matter is classified into two forms: pure form and mixture. The pure substance can be classified into elements and compound and mixture into homogeneous and heterogeneous. The International System of Measurement: SI Unit Properties of matter such as length, mass etc. can be measured quantitatively by using some systems of measurement. Such a system is the SI system established in 1960. Seven SI base units are: Physical Quantity (Dimension Symbol) Unit Name Symbol Mass (M) kilogram kg Length (L) metre m Time (T) second s Temperature (Θ) kelvin K Electric current (I) ampere A Luminous intensity (I) candela cd Amount of substance (N) mole mol 2  www.gradeup.co Derived unit: The derived unit basically refers to the unit that is derived from the basic unit. The unit of area and volume are m2 and m3 respectively that are derived from a basic unit of length (meter). Scientific notation: Chemistry deals with atoms and molecules which are present in large numbers and possess extremely low molecular masses. So in order to get the accurate value, scientific notation is used which is the exponential notation in which any number is expressed as: N x 10n ; N=1 to 10 and n = +ve or –ve. Significant figures: 1. All non-zero digits and zero present in between two non-zero digits are significant. 2. Zero present at the left of a non-zero digit is not significant. 3. Zeroes at the right of a decimal point are significant. 4. Zeroes at the left of the decimal point are not significant. Dimensional analysis: During calculations, sometimes there is a requirement of changing one unit to another. Say, the conversion of the length of a substance given in meters to inch. Thus, dimensional analysis is the conversion of a physical quantity of one type of unit to another type. 2. Laws of Chemical Combination a. Law of Conservation of Mass: It says that the matter can neither be created nor destroyed. For a chemical reaction, total mass of reactant = total mass of product. For the combustion reaction, CH4 + 2O2 ------> CO2 + 2H2O Here, 4 atoms of hydrogen, 4 atoms of oxygen and 1 atom of carbon are present in the reactant as well as in the product at the end of the reaction. Thus, the total mass of the reactant is equal to the total mass of the product. b. Law of Definite Proportions: It says that the given compound always contains the same proportion of elements by weight. For eg, water (H2O) molecule contains two atoms of hydrogen and one atom of oxygen. The molecular weight of H2O is 18g/mole i.e., it contains 2g of hydrogen and 16g of oxygen which means 11% of hydrogen and 89% of oxygen is present by weight. Thus the ratio of hydrogen to oxygen in water is 1:8. Thus, despite the number of moles of water present, the ratio of hydrogen to water will remain the same (1:8). c. Law of multiple proportions: It says that if two elements combine together to form several compounds, the weight of one of these elements that combines with a fixed weight of the other, are in the ratio of simple numbers. 3  www.gradeup.co For example, hydrogen and oxygen combines to give rise to water(H2O) molecule and hydrogen peroxide (H2O2). Hydrogen + Oxygen ------> Water 2g 16 g Hydrogen + Oxygen ------> Hydrogen peroxide 2g 32g Thus, it is seen that that oxygen combines with hydrogen with a fixed mass of ratio 1:2. d. Gay Lussac’s law: According to this law, gases when combine or form in a chemical reaction, they do so by simple ratio volume provided all gases are at constant pressure and temperature. This law is valid only in the case of gases, not for liquids or solids involved in the reactant. For example, Hydrogen + Oxygen ---> Water 100 mL 50mL 100mL This means the ratio of combining hydrogen and oxygen is a simple number ratio of 1: 2. 3. Dalton’s Theory of Atoms: The idea that matter consists of indivisible atoms led to the postulates of Dalton’s atomic theory: 1. Matter consists of indivisible atoms 2. All the atoms of an element have identical properties and identical mass. Atoms of different elements differ in mass. 3. Compound formation takes place when atoms of different elements combine in a fixed ratio. 4. A chemical reaction involves reorganization of atoms. They are neither created nor destroyed in a chemical reaction. The law of chemical combinations can be explained by this theory. 4. Limitations of Dalton’s theory of atoms: This law does not explain about 1. Law of gaseous volumes 2. Why similar or different atoms combine to form a molecule 3. Different physical properties of atoms 4. Nature of binding force between atoms of molecules. 4 www.gradeup.co 5. Atomic and Molecular Mass Atomic mass unit (a.m.u): Mass present in one-twelfth the mass of the C-12 atom is a.m.u 1 a.m.u=1.66 x10-24 g Average atomic mass: ∑ Average atomic mass = Molecular mass: Sum of the atomic mass of each element by the number of its atoms. Formula mass: Sum of atomic masses of all atoms in formula unit. Formula unit: Ratio of different ions in the compound Molar mass: Mass of one mole of a substance present in grams (g) expressed in g/mol. Molar volume: Empirical formula: It is the simplest ratio of constituent atoms. Molecular formula: Molecular formula = empirical formula x n; where, n= molecular formula mass/empirical formula mass 6. Mole Concept and Stoichiometry Balancing a chemical reaction: A balanced chemical reaction possesses same number of atoms on both the reactant and product side of the chemical reaction. For example, 4Fe  3O 2 2Fe 2 O 3 is a balanced chemical reaction. is an unbalanced chemical reaction In order to balance the above chemical reaction, following steps must be followed. 5  www.gradeup.co 1. Writing the correct formula of the reactant and product Balance the number of N atoms.Since, 2 nitrogen atoms are present in the reactant side so, the product requires 2 atoms of nitrogen. Thus, 2 molecules of ammonia (NH3) are required in the product side. 3. Balance the number of H atoms. In the reactant side, 2 atoms of hydrogen are present and 6 atoms in the product side. Thus, 4 more atoms of hydrogen must be required in the reactant side to balance the reaction. 4. Verify the number of atoms present on both the reactant and product. It is seen that 2 atoms of nitrogen and 6 atoms of hydrogen are present on both the side of reactant and product. Thus, the balancing of a chemical reaction takes place. Limiting reagent: Reactions are sometimes carried out even when reactants are present in lesser amount than that required for a balanced chemical reaction. Thus, the reactant which is present in small amount gets consumed in shorter period of time and the reaction does not continue further.This means the reactant present in smaller amount limits the product formation. Such reactants are termed as the limiting reagent. Gram equivalent or equivalent weight and its calculation: Equivalent weight Molarity(M): It is the number of moles of solute per litre of the solution. Normality (N): It is the number of gram equivalents of solute per litre of the solution. Molality (m): It is the number of moles of solute per kilogram of the solvent 6 www.gradeup.co Terms used: W = mass of the solvent in kg., w= mass of the solute, E = equivalent mass of solute V = volume of the solution in litres Relation between normality (N) and molarity (M): N = n x M; n = acidity or basicity Mass percentage(%) : Mole fraction: Mass fraction: Percentage yield: ⁄ Percentage (%) purity: 7 www.gradeup.co Attempt the free Mock Test here All the best! Team Gradeup Download Gradeup, the best IIT JEE Preparation App Attempt subject wise questions in our new practice section and JEE Main Previous Year Papers 8 www.gradeup.co 9