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Understanding The Mole in Chemistry: A Comprehensive Guide

Learn about the concept of the mole in chemistry, including its definition, Avogadro's number, and real-world examples. Explore mole-to-mass and mass-to-mole conversions, as well as calculating molar mass and average atomic mass.

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Understanding The Mole in Chemistry: A Comprehensive Guide

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  1. The mole Chapter 7 p. 224 Unit 3 “Hard work has made it easy. That is my secret. That is why I win” - Nadia Comaneci, gymnast

  2. 7.1 Intro to the mole • A dozen is a useful unit to use when baking with eggs • But a dozen is not a useful unit to use when working with atoms and molecules • You could not even see a dozen atoms! • Instead of using a dozen, chemists use a counting unit called THE MOLE • (abbreviated as mol)

  3. 7.1The Mole Notes TheSIunitusedtomeasureatomsandmolecules(particles)Themoleisdefinedintermsoftheisotopecarbon-12(12gramsofC-12containsonemoleofatoms). The SI unit used to measure atoms and molecules (particles). The mole is defined in terms of the isotope carbon-12(12 grams of C-12 contains one mole of atoms). Avagadro’s number 6.022 x 1023

  4. 7.1 The mole One dozen eggs contains 12 eggs. One mole of carbon contains 6.022 x 1023 carbon atoms.

  5. 7.1 The mole

  6. 7.1 Mole Facts Read/listen • One mole of paper would make a stack that would reach to the moon more than 80 billion times • One mole of grains of sand would be more than all of the sand on Miami Beach

  7. 7.1 Mole Facts Read/listen • One mole of blood cells would be more than the total number of blood cells found in every human on earth • One mole of inches would be1,616,434 light years, or across our galaxy and back 8 times • One mole of seconds is about 19 quadrillion years, 4,240,666 times the age of the earth, or 954,150 times the age of the universe itself

  8. 7.1 mole – mass conversion Learning Target “Students learn how to convert between mass and moles.” Overview: P. 230

  9. scratch paper What is the mass of 3 bags of m&m’s? (conversion factor: 1 bag = 46.2g) ANS = 139 g We use the mass of a bag of m&m’s as a kind of conversion factor 7.1 Real World Example

  10. 7.1 Mole to mass conversion What is the mass of 2.5 mole of carbon? moles x conversion factor = mass • The conversion factor in this problem is called molar mass

  11. 7.1 Mole to mass conversion Molar mass is defined as the mass (in grams) of one mole of substance The molar mass of any element can be found on the periodic table. For carbon: 1 mole C = 12.01 g

  12. 7.1 Mole to mass conversion What is the mass of 2.5 mole of carbon? (1 mole C = 12.01 g) S: 2.5 mol x 12.01 g/mol S: 30g

  13. 7.1 mole to mass conversion Practice: Calculate the mass of 4.5 moles of iron. 1 mole Fe = 55.85g ANS = 4.5 mol x 55.85 g/mol = 251 g

  14. 7.1 mole – mass conversion Learning Target “Students learn how to convert between mass and moles.” Overview: P. 230

  15. 7.1 Mass to mole conversion Scratch paper How many moles are there in 76 g of copper? (1 mole Cu = 63.55 g) ANS = 1.2 mole

  16. 7.1 Mass to mole conversion Calculate the number of moles in 10.6 g of gold. (1 mole Au = 196.97 g) ANS = 0.0538 mol

  17. 7.1 Molar mass e.g. 1 mole Mg = 24.31 grams This equality can be rearranged into two different conversion factors, depending on your given and your unknown Convention: given as g / mol say: “grams per mole” Same as: 1 bag M&Ms = 46.2 g

  18. 7.1 mole to mass conversion Molar mass can also be used for compounds…….. Practice: Calculate the mass of 0.45 moles of potassium chloride (1 mole KCl= 74.55 g) (molar mass of KCl= 74.55 g/mol) ANS = 0.45 mol x 74.55 g/mol = 34 g

  19. 7.1 Mass-mole conversion Practice p. 252 # 31, 33, 34, 38, 40, 41 (remember to convert kg to g where necessary) Show work to teacher when complete

  20. Summary Mole-to-mass conversion: G: mole U: grams Multiply by g/mol or, ‘Multiply by molar mass’ Mass –to-mole conversion: G: grams U: moles Multiply to mol/g Or, ‘Divide by molar mass’

  21. 7.2 Calculating Molar Mass • Read p. 234-238 Learning Target Students learn how to calculate the molar mass of a compound.

  22. Calculate the mass of one mole of propane. C3H8 ANS = 44.11 g/mol Practice: Calculate the molar mass of octane, C8H18 7.1 Calculating molar mass of a molecule

  23. 7.2 Molar mass calc Practice: p. 239 #1a-f p. 240 #10a-e, 12 a-d

  24. Practice Calculate the mass of 0.35 mole of calcium phosphate, Ca3(PO4)2 Hint: first calculate the molar mass of calcium phosphate = 310.18 g/mol ANS = 109g

  25. 7.2 Average Atomic Mass • Why are the atomic masses of the elements not whole numbers? • E.g. Cl is 35.45 amu • b/c atomic mass is a weighted average

  26. 7.2 Average Atomic Mass Chlorine is approx 75% Cl-35 and 25% Cl-37 So the average weighted mass is approx 35.5 amu

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