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February 24, 2014

- Chemical Formulas
- The Mole
- One-Step Molar Conversions

Materials

- Calculator
- Periodic Table
- A good attitude about math

Chemical Formulas

- Covalent: C8H18
- Octane
- # Carbon: 8
- # Hydrogen: 18
- Ionic: Al2(SO4)3
- Aluminum Sulfate
- # Aluminum: 2
- # Sulfur: 3
- # Oxygen: 12
- (4 O’s in each sulfate, 3 sulfates in the compound, 3 x 4 = 12)

Formula Mass

- The mass of one molecule, formula unit, or ion.
- Calculate by adding atomic masses together from the periodic table.
- Units: amu (atomic mass unit)

Example: HCl

- Mass H + Mass Cl
- 1.0079 + 35.453 = 36.4069 amu

Example: NH4NO3

- Mass N + 4(Mass H) + Mass N + 3(Mass O)
- 14.007 + 4(1.0079) + 14.007 + 3(15.999) =
- 80.0426 amu
- OR
- 2(Mass N) + 4(Mass H) + 3(Mass O)
- 2(14.007) + 4(1.0079) + 3(15.999) =
- 80.0426 amu

Example: PO43-

- Mass P + 4(Mass O)
- 30.974 + 4(15.999) = 94.97 amu
- The charge does not affect the mass because the mass of an electron is so very small that it is negligible (able to be ignored).

The Mole

- 1 mole = 6.02 × 1023 particles
- It is the number of atoms in exactly 12.0 g of carbon-12
- It is used the same way as:
- A dozen (12)
- A pair (2)
- A score (20)

Avogadro’s number

How did they come up with 6.02 x 1023anyway?

- If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro’s number of 6.02214154 x 1023 particles per mole.

Chemical Formulas

- Covalent: C8H18
- Octane
- Moles Octane: 1
- Moles Carbon: 8
- Moles Hydrogen: 18
- Ionic: Al2(SO4)3
- Aluminum Sulfate
- Moles aluminum sulfate: 1
- Moles Aluminum: 2
- Moles Sulfur: 3
- Moles Oxygen: 12

Molar Mass

- Mass of one mole(6.022 × 1023) of any molecule, formula unit, or ion.
- Calculate by adding atomic masses together from the periodic table.
- Units: g/mol

Example: H2SO4

- 2(Mass H) + Mass S + 4(Mass O)
- 2(1.0079) + 32.066 + 4(15.999)
- 98.0178 g/mol

Example: Ca(NO3)2

- Mass Ca + 2(Mass N) + 6(Mass O)
- 40.078 + 2(14.007) + 6(15.999) =
- 164.086 g/mol
- OR
- Mass Ca + 2((Mass N) + 3(Mass O))
- 40.078 + 2((14.007) + 3(15.999)) =
- 164.086 g/mol

Example: How many moles are in 2.0 g calcium chloride?

- Start with: g
- End with: moles
- Math: divide by molar mass
- Molar mass of calcium chloride, CaCl2
- 40.078 + 2(35.453) = 110.984 g/mol
- 2.0 g CaCl2= 0.018 mol

110.984 g/mol

Example: How many grams are in 1.5 molpotassium iodide?

- Start with: moles
- End with: g
- Math: multiply by molar mass
- Molar mass of potassium iodide, KI
- 39.098 + 126.90 = 165.998 g/mol
- 1.5 mol x 165.998 g/mol = 248.997 g

Molar Conversions

- Number of particles
- Formula unit
- Molecule
- Ion
- Atom

Amount in

moles

Multiply by

Avogadro’s #

Divide by

Avogadro’s #

Example: How many formula units are in 6.0 molcalcium bromide?

- Start with: mol
- End with: formula units (particles)
- Math: multiply by Avogadro’s number
- 6.0 mol x 6.02 x 1023 =3.612 x 1024 f. units
- Calculator Help: Use the EE button
- EE = x 10
- 6.02 x 1023 = 6.02EE23

Example: How many moles are in 5.0 × 1022 molecules H2?

- Start with: molecules (particles)
- End with: moles
- Math: divide by Avogadro’s number
- 5.0 x 1022 molecules= 0.083 mol
- 6.02 x 1023 molecules/mol
- Calculator Help: Use the EE button
- 6.02 x 1023 = 6.02EE23

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