Academic Chemistry

Unit 9

Counting Atoms Using Moles

Vocabulary:

Mole (81)Formula Mass(221) Empirical Formula (229)

Avogadro’s number (81)Percentage Composition (227) Molar Mass (81)

Textbook Reading and Homework:

3-3Counting Atoms pages 80-85p 85 Problems#5, 6, and 7

7-3Using Chemical Formulas pages 221-228p 228Problems #3-6

7-4Determining Chemical Formulas pages 229-233 p233 Problems #1-3

EOC’s p87 #17ace, 18a, 21a, 22a, 23a, 24a, 28a

p 235 #31a, 32a, 33a, 36

Objectives:

By the end of this unit you should…

  1. Define the mole in terms of Avogadro’s number
  2. Define molar mass and be able to use the periodic table to determine a compound’s molar mass
  3. Solve problems involving mass in grams, amount in moles, and number of atoms of an element.
  4. Use molar mass to convert between mass in grams and amount in moles of a chemical compound.
  5. Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound.
  6. Calculate the percent composition of a given chemical compound.
  7. Define empirical formula and explain how the term applies to ionic and molecular compounds.
  8. Determine an empirical formula from either a percentage or a mass composition.
  9. Explain the relationship between the empirical formula and the molecular formula of a given compound.
  10. Determine a molecular formula from an empirical formula.

Activities and Labs:

  1. Lab: Molar Mass Samples
  2. Lab: Percent Sugar in Gum
  3. Lab: Percent Water in a Hydrate

Molar Mass Worksheet

Calculate the molar masses of the following chemicals. Your answer must be rounded correctly in appropriate significant figures using the classroom periodic tables for data.

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  1. Cl2
  2. KOH
  3. BeCl2
  4. FeCl3
  5. BF3
  6. CCl2F2
  7. Mg(OH)2
  8. UF6
  9. SO2
  10. H3PO4
  11. (NH4)2SO4
  12. CH3COOH
  13. Pb(NO3)2
  14. Ga2(SO3)3

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Avogadro’s Number and Molar Conversions

  1. Find the number of moles in 2.11 x 1024 atoms of copper.
  2. Find the number of moles in 3.01 x 1023 formula units of NaCl.
  3. Find number of moles in 3.990 x 1025 molecules of CH4.
  4. Find the number of atoms in of 4.96 mol of titanium, Ti.
  5. Find the number of atoms in 237 moles of Cu.
  6. Find the number of ions in 20.0 mol Ca+2.
  7. Find the number of atoms in 155 mol of arsenic.
  8. How many moles of xenon do 5.66 x 1023 atoms equal?
  9. How many moles of AgNO3 do 2.888 x 1015 formula units equal?

Grams, Moles and Molecular Mass Worksheet

1)How many moles of sodium nitrate are in 1.70 grams of sodium nitrate, NaNO3, a substance used in fertilizers and to make gunpowder?

2)Ammonium sulfate, (NH4)2SO4, is a fertilizer used to supply both nitrogen and sulfur. How many grams of ammonium sulfate are in 35.8 moles of (NH4)2SO4.

3)A 0.500 mol sample of table sugar, C12H22O11, weighs how many grams?

4)In the early 1970s, thallium sulfate, Tl2SO4, a powerful poison, was illegally used in poison baits to control predators such as coyotes on western rangelands. Hundreds of eagles died after taking these baits. A 1.00 kilogram can of Tl2SO4 contains how many moles of this compound?

5)Ifiodine is not in a person's diet, a thyroid condition called goiter develops. Iodized salt is all that it takes to prevent this disfiguring condition. Calcium iodate, Ca(IO3)2, is added to table salt to make iodized salt.

(a)How many atoms of iodine are in 0.500 moles of Ca(IO3)2?

(b)How many grams of calcium iodate are needed to supply this much iodine?

6)Ammonium carbonate,(NH4)2CO3, is used as a fertilizer and to manufacture explosives.

(a)How many atoms of nitrogen are in 0.665 moles of this substance?

(b)How many grams of ammonium carbonate supply this much nitrogen?

7)Sodium perborate, NaBO3, is present in "oxygen bleach". It acts by releasing oxygen,which has bleaching ability. How many grams of sodium perborate are in 4.65 moles of NaBO3?

8)Barium sulfate, BaSO4, is given to patients as a thick slurry in flavored water before X-rays are taken of the intestinal tract. The barium blocks the X-rays, and the tract therefore casts a shadow that is seen on the x-ray film. How many grams are in 0.568 mole of barium sulfate.

Mole-Volume Conversions

1. Determine the volume, in liters, occupied by 0.030 moles of a gas at STP.

2. How many moles of argon atoms are present in 11.2 L of argon gas at STP?

3. What is the volume of 0.05 mol of neon gas at STP?

4. What is the volume of 1.2 moles of water vapor at STP?

  1. Determine the volume, in liters, occupied by 0.120 moles of a gas at STP.
  1. How many moles of argon atoms are present in 16.4 L of argon gas at STP?

Review and Multiple Step Mole Conversions

  1. How many moles of helium are contained in a balloon that has 3.21 x 1023 atoms?
  1. What is the mass of 0.533 moles of helium?
  1. Convert 4.5 x 1024 atoms of helium to grams of helium
  1. Convert 2.55 grams of CH4 to molecules of CH4
  1. Convert 3.2 x 1022 molecules of H2O to grams H2O
  1. Convert 105 grams of H2O to molecules of H2O
  1. What is the mass of 3.4 x 1025 molecules of CO2?
  1. What is the mass of 1.23 x 1022 atoms of He?

WORKSHEET ON EMPIRICAL AND MOLECULAR FORMULAS

1. A compound contains 26.6% potassium, 35.4% chromium, and 38.0% oxygen by mass. What is its empirical formula?

2. Iron forms two different compounds with oxygen. One is found to contain 77.7% Fe and22.3% O, while the other is found to contain 69.9% Fe and 30.1% O by mass. Find theempirical formulas of each compound.

3. Methanol contains 37.5% carbon, 12.6% hydrogen, and 49.9% oxygen by mass. If themolar mass of methanol is 32.0 g/mol, calculate its empirical and molecular formulas.

4. A compound with a molar mass of 140.3 g/mol contains 85.6% carbon and 14.4%hydrogen by mass. What is its molecular formula?

5. Find the molecular formula of a sugar containing 40.0% carbon, 6.7% hydrogen, and53.3% oxygen. (The molar mass of the sugar is 180 g/mol).

6. Find the molecular formula of a compound, given that a 212.1 gram sample of thecompound contains 42.4 grams of hydrogen and 169.7 grams of carbon. (The molarmass of the compound is 30.0 g/mol).

7. A compound with a molar mass of 284 g/mol contains 43.7% phosphorus and 56.3%oxygen. What is its molecular formula? What is the name of the compound?

8. Propylene glycol contains 47.35% carbon and 10.6% hydrogen. The remainder isoxygen. If the molar mass is 76.1 g/mol, what are the empirical and molecular formulas ofpropylene glycol?
Percent Composition and Chemical Formulas

1)Methyl ether has the molecular formula C2H6O. Find the Percentage Composition of all the elementsMolar Mass of C2H6O =

2)MDMA, or methylenedioxymethamphetamine, is the chemical name for the rave drug X or Ecstasy. It has been implicated in a number of deaths of its users. It has the following percent composition. Determine its empirical formula.

68.36% C

7.84% H

7.25% N

16.56% O

3)Ciprofloxacin, the Bayer antibiotic commonly known as Cipro is the primary medical treatment drug for inhalation anthrax, gaining attention from a terrorist attack on the US Postal system just after the infamous 9/11 terrorist attack in 2001. First approved for use in 1987, it has a formula mass of 271.33 g and the following percent composition by mass. Determine its molecular formula.

53.12% C

6.700% H

7.003% F

15.49% N

17.69% O

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