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Moles & Conversions

Moles & Conversions. 2.3, 3.3, & 9.1. Atomic Mass & Formula Mass. Atomic Mass. is the mass of one atom and is listed on the periodic table with units of amu. Atomic Mass. Samples: H Li O F Al. Masses:. Formula Mass.

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Moles & Conversions

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  1. Moles & Conversions 2.3, 3.3, & 9.1

  2. Atomic Mass&Formula Mass

  3. Atomic Mass • is the mass of one atom and is listed on the periodic table with units of amu.

  4. Atomic Mass Samples: • H • Li • O • F • Al Masses:

  5. Formula Mass • is the sum of the atomic masses of all atoms in a compound with units of amu.

  6. Formula Mass Samples: • H2O • LiOH • OF2 • AlF3 Masses:

  7. Mole,Avagadro’s Number&Molar Mass

  8. Mole • In chemistry, we need a way to count atoms and other small particles. We use something called the mole for this. It is a counting number like: • 1 pair = 2 • 1 dozen = 12

  9. Mole • 1 mole = 6.022 x 1023 particles (particles may be atoms, molecules, or formula units)

  10. Avagadro’s Number • To find the number of particles in a mole, scientists used the number of atoms in 12 g of C-12 as a standard. In that sample, there are 6.022 x 1023 C-12 atoms.

  11. Avagadro’s Number • That number of C-12 atoms in 12 g is called Avagadro’s number.

  12. Avagadro’s Number • Avagadro’s number is defined as the number of particles in exactly one mole of a pure substance which is always 6.022 x 1023.

  13. What’s in a mole? • 6.022 x 1023 atoms per mole (of atoms) • 6.022 x 1023 molecules per mole (of molecules) • 6.022 x 1023 formula units per mole (of formula units)

  14. What’s in a mole? • More than 6.022 x 1023 atoms: 1 mole CCl4 molecules is (5 × 6.022 x 1023) atoms • More than 6.022 x 1023 atoms: 1 mole NaCl formula units is (2 × 6.022 x 1023) atoms.

  15. Molar Mass • is the mass of one mole of a compound with units of grams.

  16. Molar Mass • The atomic mass on the periodic table can also be used for the molar mass of an element - switch amu with g.

  17. Molar Mass • 1 mole H atoms = _ atoms = _ g • 1 mole N atoms = _ atoms = _ g • 1 mole S atoms = _ atoms = _ g

  18. Molar Mass • Why are there different masses? • atoms have different masses just like 12 eggs have different mass than 12 grapefruit • this is due to the varying numbers of protons, neutrons, & electrons

  19. Mole Conversions • will use dimensional analysis to solve problems. • allow us to convert between moles, particles (atoms, molecules, etc.), mass, and volume. • use the molar masses and/or volumes for solving problems.

  20. Mole Conversions • If there are 16 g of S, how many moles are there? • If there are 2 moles of N atoms, what would the mass be?

  21. Mole Conversions • Find the mass in grams of 3.50 moles of Cu. • If you have 11.9 g of Al, how many moles do you have?

  22. Mole Conversions • How many moles of Ag are in 3.01 x 1023 atoms? • What is the mass in grams of 1.20 x 108 atoms of Cu?

  23. Mole Conversions Molar volume • the volume of 1 mole of gas at STP equals 22.4 liters

  24. Mole Conversions • A chemical reaction makes 0.82 moles of O2 gas. What is the volume at STP? • A room has a volume of 4000. L. How many moles of air would that be (STP)?

  25. Mole Conversions • A 1.0 L flask of CO2 (@ STP) contains how many CO2 molecules?

  26. Percent Composition 7.3

  27. Percent Composition Percent Composition • is the % by mass of an element in a compound • molar mass gives 100% of compounds mass because it accounts for each element present in the compound • to get % composition, take [(mass of the element)/(molar mass of compound)] * 100%

  28. Percent Composition Percent Composition Examples… • Find the percent composition of Cu2S. • Find the percent composition of PbCl2.

  29. Percent Composition Percent Composition Examples… • Find the percent composition of Ba(NO3)2. • Find the percent composition of H in (NH4)2CO3.

  30. Percent Composition Percent Composition Examples… • Magnesium hydroxide is 54.87% O by mass. How many grams of O would be in 175 g of the compound?

  31. Percent Composition Percent Composition Examples… • Magnesium hydroxide is 54.87% O by mass. How many grams of O would be in 175 g of the compound? How many moles of O is that?

  32. Empirical & Molecular Formulas 7.4

  33. Empirical Formulas Empirical Formulas • consist of the elements’ symbols and the subscripts that show the smallest whole-number ratio of the atoms

  34. Empirical Formulas Finding empirical formulas: • Convert the % composition data to grams. (HINT: If not given grams, use 100 grams of compound to start.) • Convert the composition in grams to moles by using molar masses of the elements. (This gives a mole ratio.) • Use the numbers from mole ratio to get the smallest possible whole number ratio.

  35. Determining Empirical Formulas Ex 1) A compound has 63.52% Fe and 36.48% S. Find the simplest formula. • 1.Comp. by mass: • 2.Comp. in moles: • 3.Smallest whole # ratio: • 4.Simplest formula:

  36. Determining Empirical Formulas Ex 2) A 10.150 g substance sample contains only P & O. After analysis, it is determined that there is 5.717 g O. What is the simplest formula of the compound? • 1.Comp. by mass: • 2.Comp. in moles: • 3.Smallest whole # ratio: • 4.Simplest formula:

  37. Determining Empirical Formulas Ex 3) A compound has 26.56% potassium, 35.41% chromium, and 38.03% oxygen. Find the simplest formula for the compound. • 1.Comp. by mass: • 2.Comp. in moles: • 3.Smallest whole # ratio: • 4.Simplest formula:

  38. Determining Empirical Formulas Ex 4) A compound has 53.70% Fe and 46.30% S. Find the simplest formula. • 1.Comp. by mass: • 2.Comp. in moles: • 3.Smallest whole # ratio: • 4.Simplest formula :

  39. Molecular Formulas • We’ve now seen how to calculate empirical formulas, but that’s not always going to give the actual formula of a compound. (ex: AlCl3, Al2Cl6, Al3Cl9, etc…)

  40. Determining Molecular Formulas • What we can determine is that there is a relationship between the simplest (empirical) formula and molecular formula. • It is (simplest formula)x = molecular formula. • x is a whole number

  41. Determining Molecular Formulas • To determine the correct formula, we need the formula mass. This will be related to the molecular formula mass in the same way as the formulas were related. • (simplest formula mass)x = molec. formula mass

  42. Determining Molecular Formulas Ex 1) The simplest formula of a compound was determined to be P2O5. The formula mass was determined to be 283.889 amu. What is the molecular formula? • Find simplest mass: • Find mass relationship: • Find formula relationship:

  43. Determining Molecular Formulas Ex 2) Determine the molecular formula of a compound with an empirical formula of CH and a formula mass of 78.110 amu. • Find simplest mass: • Find mass relationship: • Find formula relationship:

  44. Determining Molecular Formulas Ex 3) A compound with formula mass of 42.08 amu is found to have a composition by mass of 85.64% C and 14.36% H. Find the molecular formula. • Comp. by mass: • Comp. in moles: • Smallest whole # ratio: • Simplest formula: • Find simplest mass: • Find mass relationship: • Find formula relationship:

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