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The Mole

The Mole. Relative atomic mass. Relative atomic mass is a weighted average of all the naturally occurring isotopes of an element. The standard upon which it is based is one-twelfth the mass of carbon-12. For molecules (covalently bonded), the term relative molecular mass is used.

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The Mole

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  1. The Mole

  2. Relative atomic mass Relative atomic mass is a weighted average of all the naturally occurring isotopes of an element. The standard upon which it is based is one-twelfth the mass of carbon-12.

  3. For molecules (covalently bonded), the term relative molecular mass is used. For ionic compounds, use relative formula mass. Both of these are calculated as sums of the relative atomic masses of the elements in the chemical formula.

  4. How to Find the Formula/Molecular Mass 1.  Write a CORRECT formula for the compound 2.  Look up the atomic mass of each element from the periodic table in the compound and round it to a whole number (EXCEPTIONS: round Cl to 35.5 and Cu to 63.5). 3.  Multiply the rounded atomic mass by the subscripts, if any. 4.    Add all masses of elements together

  5. Example Ex: Find the formula mass of calcium phosphate 1.        Ca3(PO4)2 2.  Ca = 40 x 3 = 120 3.       P = 31 x 2 = 62 O = 16 x 8 = 128 310

  6. Examples l.  Find the formula mass of ammonium sulfate  2. Find the molecular mass of dichlorine heptoxide

  7. Answers • (NH4)2SO4 = 132 • Cl2O7 = 183

  8. Units? Same numbers can be used to calculate the mass of a single molecule or a MOLE of molecules. Single molecule unit: amu MOLE of molecules: grams per mole

  9. Relative Masses • A golf ball weighs 17 times more than a ping pong ball. • 10 golf balls will be 17 times heavier than 10 ping pong balls • 1000 golf balls will be 17 times heavier than 1000 ping pong balls • The relative mass is the same no matter how many you have.

  10. Relative Masses • The masses on the periodic table are relative masses. • One carbon atoms weighs 12 times more than one hydrogen atom • 10 carbon atoms weighs 12 times more than 10 hydrogen atoms • 1000 carbon atoms weighs 12 times more than 1000 hydrogen atoms

  11. Molar Mass 12 g of carbon-12 contains 6.02 x 1023 atoms of carbon-12. This number is known as Avogadro’s constant. One mole of any substance contains 6.02 x 1023 representative particles. The molar mass (M) of any substance is calculated using the same numbers as relative atomic/molecular/formula mass with the units of grams per mole.

  12. Measuring Matter There are three ways to measure matter: by counting representative particles (typically molecules or formula units), by mass (in grams), or by volume (in liters for gases). The method used is usually chosen by the ease of each method and the information needed. Once a measurement has been made, it is possible to convert between the units for the other methods.

  13. Measuring Matter 1 mole of a compound = molar mass in grams 1 mole of an element = 6.02 x 1023 atoms of that element 1 mole of a compound = 6.02 x 1023 representative particles 1 mole of a gas = 22.4 liters The mole is the link between grams, the number of representative particles and liters! For neutral compounds, the representative particle is either the molecule (covalent) or the formula unit (ionic).

  14. Mole Road Map

  15. Mole Practice: One Step Conversions: Remember to show all work using dimensional analysis. • How many moles are in 18.0 grams of sugar (C6H12O6)?

  16. Mole Practice: One Step Conversions: Remember to show all work using dimensional analysis. 2. What is the weight in grams of 4.50 moles of barium sulfide?

  17. Mole Practice: One Step Conversions: Remember to show all work using dimensional analysis. 3. How many moles are in 3.90 x 1028 molecules of methane (CH4)?

  18. Mole Practice: Multi Step Conversions: 7. How many formula units are in 198.5 grams of sodium chloride?

  19. Mole Practice: Multi Step Conversions: 9. How many grams are in 3.21 x 1024 formula units of potassium hydroxide?

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