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Chapter 10 Chemical Quantities

Chapter 10 Chemical Quantities. 10.1 Formula Mass and the Mole. Chemistry. Today we are learning to:- 1. Describe what is meant by formula mass . 2. Understand haw to calculate the gram formula mass of a compound. 3. Calculate the percentage composition of a compound. Formula Mass.

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Chapter 10 Chemical Quantities

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  1. Chapter 10 Chemical Quantities 10.1 Formula Mass and the Mole

  2. Chemistry Today we are learning to:-1. Describe what is meant by formula mass. 2. Understand haw to calculate the gram formula mass of a compound. 3. Calculate the percentage composition of a compound

  3. Formula Mass Review: From Chapter 4.3 Carbon-12 is the standard reference isotope. A Cabon-12 atom has a mass of exactly 12 atomic mass units. An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 atom. This means that 1 AMU is about the mass of one proton or neutron • Review: From Chapter 4.3 • Average Atomic Mass is the weighted average mass of the isotopes occurring in an element. • A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.

  4. Exothermic and Endothermic Processes 17.1 Formula Mass • This is the mass of the smallest unit of a compound measured in amu. • Just add up the relative atomic masses of all the atoms in a compound to find its formula mass. Ex. What is the formula mass of K2CO3? 1. Identify the knowns and unknowns Formula = K2CO3 Atomic masses from periodic table Formula mass = ? 2. Determine the number of atoms of each element Element Number of atoms K C O 2 1 3 3. Multiply the atomic mass of each element by how many of each you have. Then add the masses to get the formula mass. For K  2 x 39.1 amu = 78.2 amu For C  1 x 12.0 amu = 12.0 amu For O  3 x 16.0 amu = 48.0 amu formula mass =138.2 amu

  5. Exothermic and Endothermic Processes 17.1 Gram Formula Mass • This is the formulamass expressed in grams instead of amus. • So the gram formula mass of K2CO3 is 138.2g You can do this because: 1 mole of any substance contains 6.022 x 1023 atoms/molecules 1 carbon-12 atom is defined as 12 amu 1 mole of carbon-12 = 12g 1 mole of carbon = its average atomic mass = 12.001g 1 mole of potassium = its average atomic mass = 39.098g 1 mole of oxygen = its average atomic mass = 15.999g 1 mole of K2CO3 = its gram formula mass = 138.2g

  6. Exothermic and Endothermic Processes 17.1 Gram Formula Mass • Try Review questions 1-13 on page 47 of review book.

  7. END OF SHOW

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