Chapter 3.1 The Mole
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Stoichiometry
the study of the quantitative aspect of formulas and reactions
Mole
SI unit for amount of substance *the amount of a substance that contains the same number of entities as the number of entities as the number of atoms in 12g of carbon-12
Avogadro’s Number
1 mole contains 6.022x10^23 entities (to four sig figs)
Mole relating to Elements
mass in atomic mass units (amu) of one given atom of an element is the same numerically as the mass in grams of 1 mole of atoms of the element
Example of Mole relating to Elements
ex. 1 atom of element S has a mass of 32.07 amu, and 1 mole (6.022x10^23 atoms) of element S has a mass of 32.07grams
Mole Relating to Compounds
the mass in atomic mass units (amu) of one molecule (formula unit) of a compound is the same numerically as the mass in grams (g) of 1 mole of the compound
Example of Mole relating to Compounds
1 Molecule of H2O has a mass of 18.02 amu, and 1 mole (6.022x10^23 molecules) of H2O has a mass of 18.02g
Molar Mass (MM)
Mass per mole of its entities (atoms, ions, molecules, formula units) and has units of grams per mole (g/mol)
What is needed to calculate Molar Mass?
The periodic table
How to find the Molar mass of an element
look up atomic mass and find out if it is monatomic or molecular
Molar Mass of Monatomic Element…?
is equal to the Periodic table value in grams per mole
Molar Mass of Molecular Element…?
know how many molecules the element likes to be in
Example of Molar Mass of Molecule Element (In air, oxygen exists as O2, so the Molar Mass of oxygen is…?
Molar Mass O2 = 2 x Molar Mass of O = 2 x 16.00 g/mol = 32.00 g/mol
How to find the Molar Mass of a Compound
the molar mass is the sum of the molar masses of the atoms in the formula
Example of Molar Mass of a Compound (what is the Molar Mass of SO2?)
Molar Mass SO2 = Molar Mass of S + (2 x Molar Mass of O) = 32.07g/mol + (2 x 16.00g/mol) = 64.07g/mol
Converting between AMOUNT and MASS: (Moles to Grams)
*Multiply by the Molar Mass: Mass (g) = (amount (in moles) x (number of grams/1 mole))
Converting between AMOUNT and MASS: (Grams to Moles)
*Divide by the Molar Mass: Amount (moles) = (Mass (in grams) x (1 mole/number of grams))
Converting between AMOUNT and NUMBER: (Moles to Entities)
*Multiple by Avogadro’s Number: Number of entities = amount (moles) x [(6.022x10^23 entities)/(1 mole)]
Converting between AMOUNT and NUMBER: (Entities to Moles)
*Divide by Avogadro’s Number Amount (moles) = number of entities x [(1 mole)/(6.022x10^23)]
Going from Moles of Compound to Moles of Element
Use Chemical Formula: *Subscripts = Moles of element in compound
Mass Percent Equation of any Element in a COMPOUND
Mass % of any Element in a Compound = ([(atoms of Element S in formula) x (atomic mass of X)] / (Molecular mass of compound in amu)) x 100
Mass Percent Equation of each Element on a mole basis
Mass % of Element = ([(moles of X in formula) x (molar mass of X in g/mol)] / (mass in g of 1 mole of compound))
Equation to find the Mass of an Element from its Mass percent
Mass of Element = mass of compound x (mass of element in 1 mole of compound/ Mass of 1 mole of compound)