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The Mole (mol)

Avogadro’s number. The Mole (mol). The mole (abbreviation: mol ) is the amount of substance equal to 6.02 x 10 23 particles. These particles can be atoms, ions, formula units,molecules, electrons, etc. 1 mole of Carbon= 6.02 x 10 23 carbon atoms.

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The Mole (mol)

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  1. Avogadro’s number The Mole (mol) The mole (abbreviation: mol) is the amount of substance equal to 6.02 x 1023particles These particles can be atoms, ions, formula units,molecules, electrons, etc. 1 mole of Carbon= 6.02 x 1023 carbon atoms 1 mole water= 6.02 x 1023water molecules 1 mole NaCl= 6.02 x 1023 NaCl formula units 1 mole of H+ = 6.02 x 1023 H+ ions IN GENERAL: 1 mole of a substance = 6.02 x 1023particles

  2. Examples (# of particles) How many atoms of Lithium are in 0.43 moles of Li atoms? 6.02 x 1023 1 Atoms of Li 2.6 x 1023atoms of Li x 0.43 mol of Li = mol of Li How many moles of sodium ions are if we have 2.00 X 1032 sodium ions 1 mol of Na+ 3.32 x 108mol of Na+ 2.00 x 1032 ions of Na+ x = ions of Na+ 6.02 x 1023

  3. More examples (# of particles) How many moles of carbon dioxide are if we have 6.00 x 1024 molecules of carbon dioxide? 1 mole of CO2 x 9.97 moles of CO2 6.00 x 1024 molec of CO2 = 6.02 x 1023 molec of CO2 How many formula units of sodium chloride are in 0.25 moles of sodium chloride? 6.02 x 1023 1 Formula units of NaCl 1.5 x 1023form. Units of NaCl x = 0.25 mol of NaCl mol of NaCl

  4. Molar Mass and Atomic Mass Molar Mass: The mass of one mole of substance ( 6.02 x 1023particles). It is equal to the atomic mass from the periodic table , expressed in grams. Atomic mass: the average mass of all the isotopes of an element considering their percentage of abundance. The atomic mass can be expressed in amu´s (mass of atoms) or in g (mass of mole of atoms). An amu (atomic mass unit) is the mass of 1/12 the mass of one atom of 12C.

  5. Molar Mass The molar mass can be: atomic mass(for atoms),molecular mass(for molecules)orformula mass (for salts), but the term molar mass can be applied to all of them. Examples: What is are the molar masses of Carbon, Sodium Chloride, Carbon Dioxide, Oxygen Atoms and Oxygen Molecules? Remember: 1 Mole = Molar Mass (in grams)

  6. The mole and the mass of substances What is the mass of 0.250 moles of sodium? From the Periodic Table, the molar mass of Na is 22.99g 22.99 1 g Na = 0.250 mol Na x 5.75 g Na mol Na How many moles of methane (CH4) are in 45.0g of methane? Molar mass of CH4: 1C= 12.01 4H= 4 x 1.01= 4.04 16.05 + 1 mol CH4 2.80 mol CH4 45.0 g CH4 = x 16.05 g CH4

  7. Relative atomic and molecular mass The relative atomic massAr is the mass of an atom relative to carbon 12. It has no units. The relative molecular massMr is the mass of the molecule relative to carbon 12. It has no units. It is important to distinguish between the atomic mass (A or Ar ) of elements and the molecular mass (M or Mr ) of elements. For example, the atomic mass of chlorine is 35.45 and its molecular mass is 70.90 because it exists as Cl2

  8. 1 mol of B 3.1 x 1040atoms of B X 22.99 g Na 0.50 mol Na x 6.02 x 1023 atoms of B mol 1 mol Na Atoms of an element Mass of elements 1 mol Fe 6.02 x 1023 atoms of Ni 0.72 mol of Ni x 12g Fe x 1 mol of Ni 55.85 g Fe 1 mol 3.1 x 1040molec.NaF X 6.02x1023 molec NaF 1 mol NaCl 12g NaCl x 58.44 gNaCl Molecules of a compound or formula units of a salt. Mass of a compound 40.00 g NaOH 0.64 mol NaOH x molecCaCl2 6.02 x 1023 0.53 mol CaCl2 x 1 mol NaOH 1 mol CaCl2

  9. Atoms of an element Mass of elements ..mol Divideby 6.02 x 1023 Multiplyby the Molar Mass (of the element) Divideby the Molar Mass (of the element) Multiplyby 6.02 x 1023 Divide by 6.02 x 1023 Divideby the Molar Mass (of the compound) Multiply by 6.02 x 1023 Multiply by the Molar Mass (of the compound) Molecules of a compound or formula units of a salt. Mass of a compound

  10. Percent composition Percent composition: The percent by mass of each element in a compound. It is also called percent by mass. Formula: % composition of X = mass of X in the compound x 100% mass of the compound

  11. Examples Example 1: Calculate the percent composition of each element in sulfuric acid. Note: If the formula of the compound is not known, it can be determined experimentally. Example 2: In the laboratory 32.0 g of a compound were analyzed. The compound contained 24.0g of Carbon and 8.00g of hydrogen. What is the percent composition of the of each element in the compound Example 3: Sodium Hydrogen Carbonate, NaHCO3, also called baking soda is an active ingredient in some antacids used for the relief of indigestion. Determine the percent composition of sodium hydrogen carbonate.

  12. Empirical and Molecular Formulas Empirical formula: The formula that represents the smallest whole number ratio of types of atoms in a compound (or formula unit). (For example HO) Molecular formula: The formula for molecular compounds, indicating total atoms of each element in a compound. (For example H2O2). The molecular formula can be equal to or a multiple of the empirical formula.

  13. If the data is in percentage assume 100 g sample and use the percentages as grams of each element. To determine the empirical and molecular formulas: • Calculate the moles of each element • Divide by the smallest number of moles obtained • If the numbers are whole numbers they are the subscripts in the formula. • If the numbers are not whole numbers, multiply them by the smaller number that makes them all whole numbers. The obtained values are the subscripts in the formula.

  14. Example –   Methyl acetate, is a compound commonly used in some paints, inks, and adhesives. Determine the empirical formula of methyl acetate, with the following chemical analysis: • Percent by mass: • 48.65% C, • 8.16% H • 43.20% O

  15. To obtain the Molecular formula • To obtain the molecular formula divide the molar mass of the compound (given) by the molar mass of the empirical formula. • Multiply the subscripts of the empirical formula by the number obtained in the previous step.

  16. Example –   Methyl acetate, is a compound commonly used in some paints, inks, and adhesives. Determine the empirical formula of methyl acetate, with the following chemical analysis: • Percent by mass: • 48.65% C, • 8.16% H • 43.20% O

  17. Example: Succinic acid is a substance produce by lichens. Chemical analysis indicates it is composed of 40.68% oarbon, 5.08 % hydrogen and 54.24% oxygen and has a molar mass of 118.1 g/mol. Determine the empirical and molecular formulas for succinic acid.

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