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Dimensional Analysis

Dimensional Analysis. 1. Determine what your final unit needs to be - "what do you want" 2. Determine what unit you've been given - "what do you have" 3. Set up a ratio so your units cancel - usually: want on top / have on bottom

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Dimensional Analysis

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  1. Dimensional Analysis 1. Determine what your final unit needs to be - "what do you want" 2. Determine what unit you've been given - "what do you have" 3. Set up a ratio so your units cancel - usually: want on top / have on bottom EX: How many minutes are in a day? How many seconds?

  2. Moles • Called the “chemist’s dozen” • A really big quantity to measure really tiny things. • 6.02 x 10 23 particles per mole • Can measure atoms, molecules, formula units, ions, electrons, etc. • Allows us to convert from particles to mass (grams) or grams to particles

  3. A mole of …… • Marbles would cover the earth to a depth of 6 km. • Glasses of water would fill the earth’s oceans. • Sand grains would fill all the beaches in the world. • Paper clips would stretch to the nearest galaxy 2 million light years away.

  4. Try It • Determine the number of atoms in 2.50 mol Zn. • Given 3.25 mol AgNO3, determine the number of formulas units. • Calculate the number of molecules in 11.5 mol H2O

  5. Answers • 2.50 mol Zn x 6.02 x 1023 atoms/mol = 1.51 x 1024 atoms Zn • 3.25 mol AgNO3 x 6.02 x 1023 formula units/mol = 1.96 x 1024 formula units AgNO3 • 11.5 mol H20 x6.02 x 1023 molecules/mol = 6.92 x 1024 molecules H20

  6. Try It • How many moles are each of the following? • 5.75 x 1024 atoms Al • 3.58 x 1023 formulas units ZnCl2

  7. Answers • 5.75 x 1024 atoms Al x 1 mole/6.02 x 1023 atoms = 9.55 mol Al • 3.58 x 1023 formulas units ZnCl2 x 1 mole/6.02 x 1023 formula units = .595 mol ZnCl2

  8. Mass & the Mole • Which would weigh more a mole of helium or a mole of lead? WHY? • Atomic mass = amu / atom • Molar mass = grams / mole • Chromium has an atomic mass of 52.00 amu so its molar mass = 52.00 grams • How much would 2 moles of Cr weigh? • How much would .0450 moles weigh?

  9. Try It • Determine the mass in grams of each of the following: 3.57 mol Al 42.6 mol Si • Determine the number of moles in each of the following: 25.5 g Ag 300.0 g S

  10. Answers • 3.57 mol Al x 26.982 g/mol = 96.3 g Al • 42.6 mol Si x 28.086 g/mol = 1200 g Si • 25.5 g Ag x 1 mol/107.868 g = .236 mol Ag • 300.0 g S x 1 mol/32.065 g = 9.356 mol S

  11. Ratios to Know 1 mole = 6.02 x 1023 particles / atoms / etc 1 mole = X grams (determine X using the periodic table)

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