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Chemical Quantity

Chemical Quantity. Introducing the Mole. What do we mean by mole ?. The animal with the weird nose? The popular sauce in Mexican cuisine?

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Chemical Quantity

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  1. Chemical Quantity Introducing the Mole

  2. What do we mean by mole? The animal with the weird nose? The popular sauce in Mexican cuisine? A dark “spot” on a person’s face or body?

  3. The mole we are talking about • The mole is a counting number (like a dozen)used in chemistry to express amounts of a chemical substance • It is also referred to as Avogadro’s number • 6.022 X 1023 or 602200000000000000000000 • A VERY large amount.

  4. HOW LARGE IS IT??? • 1 mole of pennies would cover the Earth 1/4 mile deep! • 1 mole of hockey pucks would equal the mass of the moon! • 1 mole of basketballs would fill a bag the size of the earth!

  5. Examples • A dozen eggs is how many eggs? 12 • A dozen boron atoms is how many boron atoms? 12 • A mole of eggs would be how many eggs? 6.022 X 1023 • A mole of boron atoms would be how many boron atoms? 6.022 X 1023

  6. Finding the mass of one mole of an atom or molecule. To find out how much one mole weighs for an atom, you can go to the periodic table and find that element’s ____________________________. This is also referred to as an element’s _________________________. Atomic mass Molar mass

  7. Practice What is the mass of one mole of copper? Answer: 63.546 g What is the molar mass of lead? Answer: 207.2 g

  8. What about compounds? Steps to finding the molar mass of a compound Step 1: List the elements in the compound and the number of atoms you have for each element. Step 2: Write the molar mass of each element and multiply it by the number of atoms. Step 3: Add the masses for each element to get the molar mass (Make sure you are following rules for sig figs)

  9. Practice Water Formula: H2O H: (2)(1.007)+ O:(1)(16.00) = 18.01 g/mol Sodium Chloride Formula: NaCl Na: (1)(22.99)+ O:(1)(35.45) = 58.44g/mol

  10. More Practice • sodium bicarbonate • Formula: NaHCO3 • Na: (1)(22.99)+ • H: (1)(1.008)+ • C (1)(12.01) + • O: (3)(16.00) • = 84.01 g/mol • sucrose • C12H22O11 • C: (12)(12.01)+ • H: (22)(1.008)+ • O: (11)(16.00) • =342.30g/mol

  11. Molar Conversions • Write down your given and what you are trying to find • Cross out to get what you want • Use mole island (p.14 CRM) • Significant figures is determined by the given • Always include the compound and unit (remember sig figs)

  12. Example • How many moles of boron are in 25 g of boron? 25 g of B 1 mol of B = 2.3 mol of B 10.81 g of B

  13. Practice • How many moles of NaCl are in 100 g of NaCl?

  14. More conversions We now can go between mass (grams) and moles How do we go between moles and number of particles or vice versa? Remember that Avogadro’s number is the number of particles in a mole Therefore that will be our conversion factor 1 mol = 6.02 X 10 23 atoms, molecules, or representative particles

  15. Converting Moles to Number of Atoms Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol of propane (C3H8)? KNOWNS: • # moles = 2.12 mol C3H8 • 1 molC3H8 = 6.02 X 1023 molecules C3H8 • 1 molecule C3H8 = 11 atoms (3 carbon atoms and 8 hydrogen atoms) UNKNOWNS: • Number of atoms = ? 2.12 molC3H8 6.02 X 1023 molecules C3H8 11 atoms 1 molC3H8 1 molecule C3H8 = 1.4039 X 1025 = 1.40 X 1025 atoms

  16. Converting Number of Atoms to Moles Magnesium is a light metal used in the manufacture of aircrafts, automobile wheels, tools, and garden furniture. How many moles of magnesium is 1.25 X 1023 atoms of magnesium? KNOWNS: # of atoms = 1.25 X 1023 atoms Mg 1 mol Mg = 6.02 X 1023 atoms Mg UNKNOWN: Moles of Mg = ? 1.25 X 1023 atoms Mg 1 mol Mg 2.08 X 10-1 = 0.208 mol Mg 6.02 X 1023 atoms Mg

  17. Now you try • How many moles is 2.80 x 1024 atoms of silicon? • How many moles is 2.17 X 1023 representative particles of bromine?

  18. Your turn • How many atoms are in 1.14 mol SO3 ? • How many moles are in 4.65 X 1024 molecules of NO2 ?

  19. Mole-Volume relationship Volume of a Gas • Gases are difficult to weigh (mass) • The volume is effected by temperature and pressure • Gases must be compared at the same temperature and pressure when finding the amount of moles of gas we have

  20. STP Standard Temperature and Pressure • 00 and 1 atmosphere (atm) of pressure • At STP, 1 mole of any gas occupies 22.4 L • This is referred to as molar volume 1 mole = 22.4L of gas at STP

  21. Examples • What is the volume of 4.59 mole of CO2 gas at STP? 4.59 mol of CO2 22.4 L CO2 = 103 L of CO2 1 mol CO2

  22. More Practice • How many moles is 5.67 L of O2 at STP? • What is the volume of 8.8 g of CH4 gas at STP?

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