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Understanding The Science of Mole: Avogadro's Number in Chemistry

Explore the concept of "mole" in chemistry; learn how to calculate molar mass and convert between moles and grams with examples and practice problems.

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Understanding The Science of Mole: Avogadro's Number in Chemistry

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  1. THE MOLE • Not these kinds of moles, but…

  2. The Science Mole • The “mole” is just a number, the same way a “dozen” is 12 of something…. • A dozen eggs = 12 eggs • A dozen people = 12 people but 2 dozen (24) legs

  3. The mole is much MUCH larger than a dozen. • 1 dozen = 12 • 1 mole = 6.02 X 1023

  4. THE MOLE (n) A Mole is the amount of substance that contains 6.02 x 1023 (Avogadro’s #) particles of that substance The mass of a mole of any element or compound is called its molar mass. n (mole) = _________________ mass of a substance (g) molar mass of substance (g/mol)

  5. MOLAR MASS TO FIND MOLAR MASS OF SUBSTANCE add up the molar masses of the elements shown in the formula Examples: 1. H2O (water) Hydrogen = 1.0g/mol x 2 Oxygen = 16 g/mol x 1 Molar Mass = 18 g/mol 2. KNO3 (potassium nitrate) Potassium (K)= 39.1g/mol x 1 Nitrogen (N) = 14 g/mol x 1 Oxygen (O) = 16g/mol x 3 Molar mass = 101.1 g/mol THEREFORE: 1 mole of water has a molar mass of 18g/mol and 1 mole of potassium nitrate has a molar mass of 101.1g/mol.

  6. EX What is the molar mass of NaCl? Na = 1 x 23g/mol = 23 Cl = 1 x 35.5 g/mol = 35.5 58.5 g/mol What is the molar mass of (NH4)2SO4 EX N = 2 x 14 g/mol = 28 H = 8 x 1 g/mol = 8 S = 1 x 32 g/mol = 32 O = 4 x 16 g/mol = 64 132 g/mol

  7. RECALL n (mole) = _________________ mass of a substance (g) molar mass of substance (g/mol) moles grams convert

  8. EXAMPLE # 1 How many moles of hydrochloric acid are in 100 grams of hydrochloric acid (HCl)? n (# of moles)= grams molar mass n = ? g = 100 Molar Mass = 36.5g/mol n = 100 g n = 2.74 mol 36.5g/mol Hydrogen 1g/mol x 1 Chlorine 35.5 g/mol x 1 molar mass = 36.5 g/mol HCl

  9. EXAMPLE # 2 How many grams are in 11.1 moles of water (H20)? n (# of moles)= grams molar mass n = 11.1 moles g = Molar Mass = 18 g/mol 11.1 moles = _____ 18 g/mol g = 200 grams Hydrogen 1 g/mol x 2 Oxygen 16 g/mol x 1 molar mass = 18 g/mol

  10. EXAMPLE # 3 What is the mass of 0.42 moles of potassium nitrate (KNO3)? n(moles) = 0.42 moles Molar Mass = 101.1 g/mole g = ? n (# of moles)= grams molar mass 0.42 mole = __g__ 101.1 g/mole K = 39.1 g/mole N = 14 g/mole 0 = 16 g/mole X 3 = 48g/mole 101.1 g/mole g = 42.46 grams

  11. KEY POINTS • The mass of a mole of any element or compound is called itsmolar mass. • AMoleis the amount of substance that contains • 6.02 x 1023 (Avogadro’s #) particles of that substance • Formula to convert between moles and mass (g) is: EXAMPLE 1. H2O (water) Hydrogen = 1.0g/mol x 2 Oxygen = 16 g/mol x 1 Molar Mass = 18 g/mol n (# of moles)= grams molar mass

  12. PRACTICE PROBLEMS • Study guide, Module 3, page 11 and 18 • 436 WORKSHEET # 2

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