Unit 5 study guide: the Mole

  • Mass to moles & mass to moles (molar mass)
  • STP
  • diatomic molecules
  • empirical vs. molecular formulas
  • Volume of gases at STP to moles and vise versa (molar volume of gasses)
  • hydrated salts (and their formulas)
  • Particles (atoms, molecules, or formula units) to mole and moles to particles (Avogadro’s number)
  • significant figures
  • percent composition
  • Know how to find the empirical formula of a compound if given the percent composition
  • Know how to get the molecular formula given the empirical formula and molar mass
  • Know how to calculate percent error and % yield
  • Know how to write formulas if given names for compounds!!
  • Know how to determine the experimental formula of a hydrated salt.

PRACTICE PROBLEMS – do these on a separate piece of paper. Be sure to SHOWALL YOUR WORK!!

  1. Calculate the percent composition of Sodium acetate in sodium acetatepentahydrate.
  2. Now calculate the % of water in the previous question.
  3. If you have 125.5g of magnesium phosphate, what is the mass of magnesium? Phosphorus? Oxygen?
  4. You have a compound that is 40.0% C, 6.6% H, and 53.4% O. What is the empirical formula?
  5. The compound in the previous question has a molar mass of 120.0g. What is the molecular formula?
  6. If 4.04 g of nitrogen combine with 11.46 g of oxygen to produce a compound with a molar mass of 108.0 g, what is the molecular formula of this compound?
  7. A particular organic sugar is determined to have the following composition: 40.0% carbon, 6.7% hydrogen, and 53.5% oxygen. Determine the empirical formula of this sugar molecule, then determine its molecular formula if you know it’s molar mass is 180.0g.
  8. You calculated the theoretical mass of water in Epsom salts to be 55.8g. In the lab, the mass of water evaporated was only 32.6g. What was the percent error?
  9. How many moles is 175.5g of sodium sulfate tetrahydrate?
  10. How many atoms of oxygen are in the previous question? (be sure to account for the water!)
  11. You have 37.4 mL of nitrogen gas at STP. How many particles do you have? What is the particle (atom/molecule or formula unit)?
  12. How many atoms of hydrogen are in 59.29 mL of hydrogen gas at STP?
  13. You weigh an empty crucible with a mass of 22.89 g. You place 8.46 g of copper (II) sulfate pentahydrate. After heating, the crucible with the dehydrated salt weighs 25.51 g. Determine the % error of water, % error of the ionic anhydrous compound, and the experimental value of the mole ratio of the hydrated salt.

Unit 5 study guide: the Mole

  • Mass to moles & mass to moles (molar mass)
  • STP
  • diatomic molecules
  • empirical vs. molecular formulas
  • Volume of gases at STP to moles and vise versa (molar volume of gasses)
  • hydrated salts (and their formulas)
  • Particles (atoms, molecules, or formula units) to mole and moles to particles (Avogadro’s number)
  • significant figures
  • percent composition
  • Know how to find the empirical formula of a compound if given the percent composition
  • Know how to get the molecular formula given the empirical formula and molar mass
  • Know how to calculate percent error and % yield
  • Know how to write formulas if given names for compounds!!
  • Know how to determine the experimental formula of a hydrated salt.

PRACTICE PROBLEMS – do these on a separate piece of paper. Be sure to SHOWALL YOUR WORK!!

  1. Calculate the percent composition of Sodium acetate in sodium acetatepentahydrate.
  2. Now calculate the % of water in the previous question.
  3. If you have 125.5g of magnesium phosphate, what is the mass of magnesium? Phosphorus? Oxygen?
  4. You have a compound that is 40.0% C, 6.6% H, and 53.4% O. What is the empirical formula?
  5. The compound in the previous question has a molar mass of 120.0g. What is the molecular formula?
  6. If 4.04 g of nitrogen combine with 11.46 g of oxygen to produce a compound with a molar mass of 108.0 g, what is the molecular formula of this compound?
  7. A particular organic sugar is determined to have the following composition: 40.0% carbon, 6.7% hydrogen, and 53.5% oxygen. Determine the empirical formula of this sugar molecule, then determine its molecular formula if you know it’s molar mass is 180.0g.
  8. You calculated the theoretical mass of water in Epsom salts to be 55.8g. In the lab, the mass of water evaporated was only 32.6g. What was the percent error?
  9. How many moles is 175.5g of sodium sulfate tetrahydrate?
  10. How many atoms of oxygen are in the previous question? (be sure to account for the water!)
  11. You have 37.4 mL of nitrogen gas at STP. How many particles do you have? What is the particle (atom/molecule or formula unit)?
  12. How many atoms of hydrogen are in 59.29 mL of hydrogen gas at STP?
  13. You weigh an empty crucible with a mass of 22.89 g. You place 8.46 g of copper (II) sulfate pentahydrate. After heating, the crucible with the dehydrated salt weighs 25.51 g. Determine the % error of water, % error of the ionic anhydrous compound, and the experimental value of the mole ratio of the hydrated salt.