Power Point 6: Molar Conversions

Drill:Calculate the percent composition of each element in H4N2O3

Begin Molar Conversions

The Mole: The standard unit of measure for the amount of a substance

  • A Dozen = 12 of anything
  • A Mole = 6.02 x 1023 of anything
  • The amount of a substance that would = its mass in g from the Periodic Table
  • 1 mole of C = 12.0 g1 mole of SO2 = 64.0 g

Molar Conversions:

•Converting unit of a substance from mass to moles or moles to mass

•Converting the volume of a gas to moles or vice versa

•Converting the number of particles to moles or vice versa

•Converting the volume of a solution to moles or vice versa

Molar Chart:

Mass Atoms or Molecules

Moles

Gas Volume Solution Volume

Moles First: No matter what conversion you are attempting to do, convert to moles first.

Converting Mass to Moles or Vice Versa:

•Use atomic masses from the periodic table

•O = 16.0 g/moleNaCl = 58.5 g/mole

Converting Gas Volume to Moles or Vice Versa:

•At STP: 22.4 L/mole

•Non-STP: PV = nRTn =PV/RT

Converting Particles to Moles or Vice Versa:

•Use Avogadro’s Number

•6.02 x 1023 atoms, molecules, etc/mole

Converting a Solution Volume to Moles or Vice Versa:

•Multiply the molarityof the solution times its volume in Liters

•n = M x V

•Molarity (M) = the number of moles of solute per liter of solution.

Factor Label method for conversions: To convert a substance from one unit of measure to another, multiply that substance by a fraction made up of different units making the fraction = 1.

12 inches = 1 foot; thus 12 in/1 ft = 116 oz = 1 lb: thus, 1 lb/16 oz = 1

Make all of the following conversions. Show all work. Bow in answers.

•Convert 7.0 g of silicon to moles

•Convert 250 g of CaCO3 to moles

•Convert 3.0 moles of helium to grams

•Convert 11.2 L of oxygen gas at STP to moles

•Convert 0.20 moles of helium to volume at STP

•Convert 2.0 x 1024 atoms He to moles

Drill: Convert 3.0 moles of glucose to molecules:

Make all of the following conversions. Show all work. Bow in answers.

  • Convert 250 mL of 0.10 M HCl to moles
  • Convert6.8 g NH3 to volume of gas at STP
  • Convert3.0 x 1025 molecules of CO2 to mass in kg
  • Calculate the number of atoms in 16 ng of Fe2(SO4)3

Drill: Calculate the number molecules in 32 mg of Fe2O3

Empirical Formula:

•The lowest whole number ratio of elements in a compoundC6H12O6: EF = CH2O

Determining Empirical formulas from percent composition:

•Assume 100 g

•Change % directly to grams

•Use molar conversions to convert grams to moles

•Divide each molar amount by the smallest molar amount

Find empirical for a compound with:

  • 70.0 % Fe &30.0 % O
  • 40.0 % Ca & 12.0 % C & 48.0 % O
  • 40.0 % C & 6.67 % H & 53.3 % O

Molecular Formula: The actual whole number for each element in the compound

Examples: Glucose: Molecular Formula: C6H12O6Empirical Formula: CH2O

Solving a Molecular Formula from an Empirical Formula:

1) Solve molar mass of the empirical formula (empirical mass)

2) Divide the molecular mass of glucose by its empirical mass

3) Multiply all the subscripts in the empirical formula by quotient from step 2

Calculate the molecular formula of a compound whose empirical formula is CH2O and its molecular mass is 150 g/mole.

Drill: Calculate the mass of solute required to make 40.0 mL solution of 0.25 M Pb(NO3)2

Test Review on Nomenclature, Molar conversions, & % Composition

Make the following calculations. Show all work. Box in answers.

  • Calculate the molecular formula of a substance with an empirical formula of NH2 & a molecular mass of 32 g/mole.
  • Calculate the % composition of each element in Pb(NO3)2
  • Calculate the empirical formula of a substance containing 62.7 % Po, 28.8 % O,

& 8.4 % N.

Name each of the following compounds:

•SeOMgSPbO2Cl2OKNO3ScCl3

Derive formulas for each of the following compounds:

•Cesium oxideBarium chloride

•Calcium phosphateManganese(II) chlorate

Name each of the following compounds:

NH4ClBaSO4KC2H3O2K2HPO3

KNO3CuBrOLi2CO3MgC2O4

HClH2SO4H2SH3PO3

HNO3HBrOH2CO3HBrO4

Make each of the following conversions. Show all work. Bow in answers:

  • Calculate the number of hydrogen atoms in 1.8 kg of PH5
  • Calculate the volume at STP of 6.0 ng of NO.
  • Calculate the mass of KBr required to make 250 mL of a 0.40 M solution.
  • Calculate the number of oxygen atoms in 320 g of Fe2O3.
  • Calculate the mass in ngof 5.6 x 10-15 L of SO2 at STP.