Chapter 3. FORMULAS, EQUATIONS AND MOLES Mole Calculation. Dozen = 12. Pair = 2. Names associated with an amount. The Mole…. The mole (mol) is the amount of a substance that contains as many elementary entities as there are atoms in exactly 12.00 grams of 12 C.
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FORMULAS, EQUATIONS AND MOLES
Dozen = 12
Pair = 2
Names associated with an amount
The mole (mol) is the amount of a substance that
contains as many elementary entities as there
are atoms in exactly 12.00 grams of 12C
1 mol = NA = 6.0221367 x 1023
Avogadro’s number (NA)
Molar mass is the mass of 1 mole of in grams
1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g
1 12C atom = 12.00 amu
1 mole 12C atoms = 12.00 g 12C
1 mole lithium atoms = 6.941 g of Li
For any element
atomic mass (amu) = molar mass (grams)
What is the mass of one mole of:
1 mol K
6.022 x 1023 atoms K
1 mol K
39.10 g K
How many atoms are in
0.551 g of potassium (K) ?
1 mol K = 39.10 g K
1 mol K = 6.022 x 1023 atoms K
0.551 g K
8.49 x 1021 atoms K
The molar mass of a compound is found by adding
Together the molar masses of all of its elements, taking
Into account the number of moles of each element present.
+ 2 x 16.00 amu
Molecular mass (or molecular weight) is the sum of
the atomic masses (in amu) in a molecule.
For any molecule
molecular mass (amu) = molar mass (grams)
1 molecule SO2 = 64.07 amu
1 mole SO2 = 64.07 g SO2
8 mol H atoms
6.022 x 1023 H atoms
1 mol C3H8O
1 mol C3H8O
1 mol H atoms
60 g C3H8O
How many H atoms are in 72.5 g of C3H8O ?
1 mol C3H8O = (3 x 12) + (8 x 1) + 16 = 60 g C3H8O
1 mol C3H8O molecules = 8 mol H atoms
1 mol H = 6.022 x 1023 atoms H
72.5 g C3H8O
5.82 x 1024 atoms H
Quantitative relationship among reactants and products are called stoichiometry.
Stoichiometry problems are easily solved when amounts ofsubstances are converted from mass (in units of g, kg etc), volume (L), into moles.
Amounts in moles depend on how the chemical formula or the chemical reaction equations are written.
Chemical reaction equations are the basis for reaction stoichiometry, but when the reactants are not stoichiometric mixtures, some reactants will be in excess whereas others will be in limited supply.
Mass Changes in Chemical Reactions
Moles B = X Moles A
The stoichiometric ratio is used to determine amounts of compounds
consumed or produced in a balanced chemical reaction
2CH3OH + 3O2 2CO2 + 4H2O
4 mol H2O
18.0 g H2O
1 mol CH3OH
2 mol CH3OH
32.0 g CH3OH
1 mol H2O
Methanol burns in air according to the equation
If 209 g of methanol are used up in the combustion,
what mass of water is produced?
209 g CH3OH
235 g H2O
% Yield =
Theoretical Yield is the amount of product that would
result if all the limiting reagent reacted.
Actual Yield is the amount of product actually obtained
from a reaction.
The reactant that is completely consumed by the reaction
The number of bicycles that can be assembled is limited by whichever part
runs out first. In the inventory shown in this figure, wheels are that part.
A molecular view of a Limiting reactant situation for the ammonia
Synthesis. To make 4 molecules of NH3 requires 2 molecules of N2 and
6 molecules of H2. If we start with 4 molecules of N2 and 6 molecules of
H2, H2 is the limiting reactant.
Limiting Reagent: It is the reactant whose number of moles divided
By it’s stoichiometric coefficient is the smallest
2. Determine the amount of POCl3 based on the limiting reagent PCl3.
Note that the conversions of grams to Kg is not shown.
Moles of solute
Volume of solution in L
Molarity: The most useful way of expressing the amount of a substance dissolved in a solution is with molarity
Making Molar Solutions
A molar solution is one that expresses “concentration” in moles per volume
Usually the units are in mol/L
mol/L can be abbreviated as M or [ ]
Molar solutions are prepared using:
a balance to weigh moles (as grams)
a volumetric flask to measure litres
L refers to entire volume, not water!
Because the units are mol/L, we can use the equation M = n/L
Alternatively, we can use the factor label method
Making Molar Solutions