# Deptt. Of Applied Sciences Govt. Polytechnic College For Girls Patiala Presented By- Dr. Raman Rani Mittal M.Sc., M.Phil, Ph.D. (Chemistry) 1.

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Deptt. Of Applied Sciences Govt. Polytechnic College For Girls Patiala Presented By- Dr. Raman Rani Mittal M.Sc., M.Phil, Ph.D. (Chemistry) 1

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Contents  Mole Concept Atomic & Gram atomic mass Molecular mass & Gram molecular mass Mole concept & its importance  Solutions Methods of expressing concentrations of solutions 3

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Atomic & Molecular Mass Matter is made up of atoms & molecules Mass of matter is due to atoms & molecules Mass of an atom is called as atomic mass & mass of molecule is termed as molecular mass The actual mass of an individual atom or molecule is extremely small. This mass can not be expressed in grams. To express the masses of atoms & molecules, the unit called Atomic Mass Unit (a.m.u.) is introduced. 5

The atomic mass unit (amu) may be defined as one-twelfth of the actual mass of an atom of carbon (Carbon-12 isotope). The atomic mass of an element tell us as to how many times an atom of the element is heavier than 1/12 th of an atom of Carbon (C-12) Mass of an atom of an element 1/12 x mass of an atom of carbon(C-12) Atomic mass = 6

For example, atomic mass of oxygen is 16 a.m.u. It means that an atom of oxygen is 16 times heavier than 1/12 th of mass of carbon atom (C-12) The atomic mass of an element is the average relative mass of its atoms as compared with an atom of carbon taken as 12 a.m.u. 7

Gram Atomic Mass Gram atomic mass It is the quantity of an element whose mass in grams is numerically equal to its atomic mass. In simple words, atomic mass of an element expressed in grams is the gram atomic mass or it is also called gram atom For example, the atomic mass of oxygen is 16 a.m.u. and thus gram atomic mass of oxygen is 16 g. Mass in grams Gram atomic mass Number of gram-atom 8

Molecular mass Molecular mass of a substance ( element or compound) may be defined as the average relative mass of a molecule of the substance as compared with mass of an atom of carbon (C12)taken as 12 a.m.u. 9

In other words, Molecular mass expresses as to how many times a molecule of the substance is heavier than 1/12 th of the mass of an atom of carbon. For example, A molecule of CO 2 is 44 times heavier than 1/12 th of the mass of carbon atom. Hence, molecular mass of CO 2 is 44 a.m.u. 10

The molecular mass is obtained by adding together the atomic masses of various atoms present in a molecule. For example, The molecular formula of carbon dioxide is CO 2. Hence, its molecular mass is = Atomic mass of carbon + 2 x (Atomic mass of oxygen) = 12 + 2 x 16 = 44 a.m.u. 11

Gram Molecular Mass Gram molecular mass is the quantity of a substance whose mass in grams is numerically equal to its molecular mass. In other words, molecular mass of a substance expressed in grams is called gram molecular mass. It is also known as gram molecule. For example, the molecular mass of oxygen is 32 and therefore, its gram molecular mass is 32 g. Mass in grams Gram molecular mass No. of gram molecule 12

Example : Calculate the molecular mass of calcium carbonate. Solution : Molecular mass of calcium carbonate (CaCO 3 ) = 1 x atomic mass of Ca + atomic mass of C + 3 x atomic mass of O = 1 x 40 + 12 + 3 x 16 = 40 + 12 + 48 = 100 amu 13

Mole Concept In chemistry we use a unit mole to count particles (atoms, ions or molecules). A mole is a collection of 6.023 x 10 23 particles irrespective of their nature. The no. 6.023 x 10 23 is called Avogadro’s number and is denoted by N o. 1 Mole = 6.023 x 10 23 particles 14

For example, 1 mole of atoms = 6.023 x 10 23 atoms 1 mole of molecules = 6.023 x 10 23 molecules 1 mole of ions = 6.023 x 10 23 ions 1 mole of electrons = 6.023 x 10 23 electrons 1 mole of protons = 6.023 x 10 23 protons While using the term mole, it is important to indicate the kind of particles involved. 1 mole of H atoms = 6.023 x 10 23 atoms of H 1 mole of H molecules = 6.023 x 10 23 molecules of Hydrogen The mole is also related to the mass of the substance 15

1. Mole & Gram Atomic Mass Mass of one mole of atoms of any element in grams is equal to its gram atomic mass or one gram atom. One mole of atoms = 6.023 x 10 23 atoms = Gram atomic mass of the element For example, The mass of 6.023 x 10 23 atoms of oxygen is 16 grams. 16

2. Mole & Gram Molecular Mass Mass of one mole of molecules of any substance in grams is equal to its gram molecular mass. One mole of molecules = 6.023 x 10 23 molecules = Gram molecular mass For example, The mass of 6.023 x 10 23 molecules of sulphur dioxide (1 mole) is equal to 64 grams. Similarly, the mass of 6.023 x 10 23 molecules of carbon dioxide (CO 2 ) is equal to 44 grams. 17

3. Mole concept for Ionic compounds Mass of one mole of formula units of any ionic compound in grams is equal to its gram formula mass. One mole of formula units = 6.023 x 10 23 formula units = Gram formula mass For example, The mass of 6.023 x 10 23 formula units of NaCl or 6.023 x 10 23 Na + ions and 6.023 x 10 23 Cl - ions (one mole of NaCl) is equal to 58.5 g or 1 formula mass of NaCl. 18

4.Mole in terms of Volume One mole of any gas at S.T.P. (0 o C and 760 mm pressure) occupies 22.4 litres. This volume is known as molar volume. For example, 1 mole (2 grams) of H 2 gas = 22.4 litres at S.T.P. 1 mole (28 grams) of N 2 gas = 22.4 litres at S.T.P. 1 mole (32 grams) of O 2 gas = 22.4 litres at S.T.P. 1 mole (44 grams) of CO 2 gas = 22.4 litres at S.T.P. 19

One mole of a gas = 22.4 litres at S.T.P. = 6.023 x 10 23 molecules = Gram molecular mass For example, 1 mole H 2 gas = 22.4 litres at S.T.P. = 6.023 x 10 23 molecules of H 2 = 2 g 20

To calculate number of moles (a)For Elements No. of atoms of the element 6.023 x 10 23 Mass of the element in grams Gram atomic mass Number of moles 21

Example: Calculate the number of moles in 22 g of CO 2. Solution: Molecular mass of CO 2 = 12+2x16 = 44 amu Gram molecular mass of CO 2 = 44 g Since, 44 g of CO 2 make = 1 mole 18 6.023 x 10 23 g = 0.5 mole.∙. 22 g of CO 2 will make 22

(b) For Compounds No. of molecules of the compound 6.023 x 10 23 Mass of the compound in grams Gram molecular mass No. of moles 23

(c) For an assembly of things Number of things 6.023 x 10 23 (d) 1 mole = gram molecular mass = 6.023 x 10 23 = 22.4 L at S.T.P. Number of moles 24

Importance of Mole concept 1.To calculate mass of one atom of element Gram atomic mass 6.023 x 10 23 Mass of an atom of element = 25

Example : What is the mass of single atom of Hydrogen ? Solution : Atomic mass of Hydrogen = 1.008 amu Gram atomic mass of hydrogen = 1.008 g Thus 6.023 x 10 23 atoms of hydrogen have mass = 1.008 g 1.008 6.023 x 10 23 = 1.66 x 10 - 24 g Hence, a single atom of H will have mass = 26

Example : What is the mass of single atom of Carbon? Solution : Atomic mass of Carbon =12 amu Gram atomic mass of carbon = 12 g Thus 6.023 x 10 23 atoms of Carbon have mass = 12 g 12 6.023 x 10 23 = 1.99 x 10 - 23 g Hence, a single carbon atom will have mass = 27

2. To calculate mass of one molecule of the substance. Gram molecular mass 6.023 x 10 23 Mass of one molecule of substance 28

Example: What is the mass of a single molecule of hydrogen? Solution: Molecular mass of H 2 = 2 amu Gram molecular mass of H 2 = 2 g Thus, 6.023 x10 23 molecules of H 2 have mass = 2g 2 6.023 x10 23 = 3.3 x 10 - 24 g.∙. A single molecule of H 2 will have mass = 29

Example: Calculate the mass of a single molecule of water? Solution: Molecular mass of H 2 O = 2x1 + 16 =18 amu Gram molecular mass of H 2 O = 18 g Thus, 6.023 x10 23 molecules of H 2 O have mass = 18g 18 6.023x10 23 = 2.99 x 10 -23 g.∙. A single molecule of H 2 O will have mass = 30

3. To calculate the number of atoms in a given mass of the element. No. of atoms in a given mass of element Mass of element in grams Gram atomic mass x 6.023x10 23 31

Example: Calculate the number of atoms in 20g of calcium (At. Mass of Ca = 40). Solution: Atomic mass of Ca = 40 amu Gram atomic mass of Ca = 40 g Thus 40 g of Ca contains = 6.023 x10 23 atoms 6.023 x10 23 40 = 3.01 x 10 23 atoms.∙. 20g of Ca will containx20 32

4. To calculate the number of molecules in a given mass of substance. No. of molecules in a given mass of substance Mass of substance in grams Gram molecular mass X 6.023x10 23 33

Example: Calculate the number of molecules of methane in 0.80 g of methane. Solution: Molecular mass of methane (CH 4 ) = 1x12 + 4x1 = 16 amu Gram molecular mass of CH 4 = 16 g Thus 16g of CH 4 contain = 6.023 x10 23 molecules 6.023 x10 23 16 = 3.01x10 22 molecules.∙. 0.80g of CH 4 will contain x 0.80 34

5. To calculate the volume occupied by a given mass of the gas at S.T.P. Volume occupied by a given mass of a gas at S.T.P. Mass of gas in grams Gram molecular mass of gas x22.4 35

Example: Calculate the volume occupied by 16 g of oxygen at S.T.P. Solution: Molecular mass of O 2 = 32 amu Gram molecular mass of O 2 = 32 g Now 32 g of O 2 at S.T.P. occupy volume = 22.4 L.∙. 16g of O 2 at S.T.P. would occupy volume 22.4 32 = 11.2 litres x16 = 36

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Solutions Solution is a homogeneous mixture of two or more pure substances Composition of solution can be varied within certain limits. Solution results by dissolving a solute in a solvent. Solute + Solvent Solution 38

The substance which is dissolved & is present in lesser quantity is called solute. The substance in which solute is dissolved & is present in greater quantity is called solvent. For example, 2g of sugar is dissolved into 50 ml of water to form a solution. In this case sugar is solute & water is solvent. 39

Methods of expressing Concentration of a solution The concentration of solution is defined as the amount of solute present in the given quantity of the solution. It can be expressed in the following ways: 1. Strength 2. Molarity 3. Molality 4. Mole fraction 5. Normality 6. Mass percentage 7. Volume percentage 40

1.Strength: It is the amount of solute in grams dissolved per litre of the solution. Thus, Mass of solute in grams Volume of solution in litres If ‘a’ grams of solute is dissolved in V ml of a given solution, then a x 1000 V It is expressed in g/L. Strength of solution = Strength = 41

2. Molarity (M): The number of moles of solute dissolved per litre of the solution is called molarity. Number of moles of solute Volume of solution in litres It is convenient to express volume in ml. So that Number of moles of solute Volume of solution in ml Molarity = M = x1000 42

And number of moles of solute can be calculated from the given mass of solute which is dissolved Given mass Gram molecular mass Thus, Given mass x 1000 Gram mol. mass x V Molarity changes with temperature. Moles of solute = M = 43

Example: Calculate the molarity of the solution containing 0.5g of NaOH dissolved in 500 ml Solution: Given mass of NaOH = 0.5g Mol.mass of NaOH = 23 + 16 + 1= 40 0.5 40 Volume of solution, V = 500ml No. of moles of NaOH x 1000 V 0.0125 x 1000 500 No. of moles of NaOH == 0.0125 Now, Molarity = == 0.025 M 44

3. Molality: The number of moles of solute dissolved per kg of the solvent is called molality. No. of moles of solute Mass of solvent in kg No. of moles of solute Mass of solvent in grams If ‘a’ grams of the soute is dissolved in W gram of the solvent, then a 1000 mol. Mass of solute W Molality does not changes with temperature. Molality (m) = = x1000 m =x 45

Example: Calculate the molality of an aqueous solution containing 4g of urea (Mol.mass = 60) in 500 g of water. Solution: Given mass of urea = 4g Mol. mass of urea = 60 Mass of water, W = 500g Given mass 1000 Mol. mass W 4 1000 60 500 = 0.133 m Since, Molality (m) = = x x 46

4. Mole fraction (x): It is the ratio of the number of moles of a component to the total number of moles of all the components (solute & solvent) in the solution. Suppose a solution contains n A moles of solute (A) and n B moles of solvent (B). Then, n A n A + n B n B n A + n B Mole fraction of solute (x A ) = Mole fraction of solvent (x B ) = 47

The sum of mole fractions of all the components is always equal to one. n A n B n A + n B n A + n B Mole fraction being a ratio, is dimensionless property. x A + x B =+= 1 48

Example: A solution containing 23g of ethanol & 90g of water. What is the mole fraction of ethanol & water in solution? Solution: Mass of ethanol (C 2 H 5 OH) = 23g Molecular mass of ethanol = 2x12 + 1x6 + 16 = 46 23 46 Mass of water = 90g Molecular mass of water = 18.∙. Number of moles of ethanol = 49 = 0.5

90 18 = 5.∙.Total number of moles = 0.5 + 5 = 5.5 0.5 5.5 = 0.09 Mole fraction of water = 1 – 0.09 = 0.91.∙. Number of moles of water =.∙. Mole fraction of ethanol = 50

5. Normality (N): It is the number of moles of gram equivalents of the solute dissolved per litre of the given solution. No. of gram equivalents of solute Volume of solution in litres No. of g.equivalents of solute Volume of solution in ml Normality (N) = x1000Or= 51

Gram equivalents of solute can be calculated as Mass of solute a Equivalent mass Eq. mass where ‘a’ is the mass of the solute in grams present in V ml of a given solution a 1000 Eq. mass V Like molarity, normality of a solution also changes with temperature. Gram equivalents == Thus,N = x 52

6. Mass percent(w/w): It is equal to the weight of solute present per 100 g of the solution. Weight of solute Weight of solution Weight of solute in grams Wt. of solute + Wt. of solvent Mass (weight) percent can be expressed as w/w. For example, a 5%(w/w) solution of NaCl means a solution containing 5g of NaCl in 100g of the solution or 95 g of the solvent. x100 %Mass = = 53

7. Volume %age: It is equal to the volume of the component present per 100 parts of the volume of the solution. For example, V A and V B are volumes of the components A & B respectively in a solution, then Volume of A Vol. of A + Vol. of B It is expressed as v/v. Volume %age of A =X 100 54

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