Chemical Quantities. Or How I Learned to Love the Mole. A mole?. Not the type of mole we are talking about. Vocabulary. Mole Avogadro’s Number Representative Particle Molar Mass. How do you measure the amount of something?.
Or How I Learned to Love the Mole
Not the type of mole we are talking about
What are some everyday ways we count matter?
DOZEN = 12 things
1 GROSS = 144 things
What about molecules? Or atoms?
BUSHEL of corn = 21.772 kg
1 MOLE = ???
In Chemistry is NOT this furry little animal or the spot on your face…
How much is a mole?
A mole of pennies is very large.
10-2 Mass & the Mole 10-3 Moles of Compounds
Defn: is the mass (think grams) of one mole of a substance
1 mole O = 16.0 grams
1 mole N = 14.0 grams
SO3= 80 g/mole
1 Mole = 142.043g
Molar Mass Calculator for homework help
Mass = 25.0 g Au
Molar mass Au = 196.97 g/mol Au
25.0 g Au x 1 mole Au x 6.02 x 1023 atoms Au = 7.65 x 1022 atoms Au
196.97 g Au 1 mol Au
Number of atoms = ? Atoms Au
Number of atoms = 5.50 x 1022 atoms He
Molar mass He = 4.00 g/mol He
5.50 x 1022 atoms He x 1 mol He x 4.00 g He = 0.366 g He
6.02 x 1023 atoms He 1 mol He
Mass = ? G He
1.25 molAl2O3 x 2 mol Al3+ ions = 2.50 mol Al3+ ions
1 mole Al2O3
You have 10.0 grams of ordinary sugar on a scale. Sugar is sucrose and has a formula of C12H22O11.
10-3 Empirical & Molecular Formulas
Ex. Compound XY is 55g element X and 45g element Y
55 g of element Xx 100 = 55 % element X
100 g of compound
45 g of element Y x 100 = 45 % element Y
100 g of compound
% by mass H = 2.02 g x 100 = 11.2% H
18.02 g H2O
Example continued –
16.00 g x 100 = 88.8 % O
1. Select lowest number of moles
2. Divide each number of moles by this number.
3. If the number divides out evenly, these are the subscripts of the elements in the compound.
4. If any of the numbers have a .5, MULTIPLY them ALL by TWO & then place these numbers as the subscripts.
40.05 g S x 1 mol = 1.249 mol S
59.95 g O x 1 mol = 3.747 mol O
The mole ratio of S atoms to O atoms in the oxide is 1.249 : 3.747.
Recognize that S has the smallest possible number of moles at ~1. Make the mole value of S equal to 1 by dividing both mole values by 1.249.
1.249 mol S = 1 mol S
3.747 mol O = 3 mol O
The simplest whole number mole ratio of S atoms to O atoms is 1 : 3. The empirical formula for the oxide of sulfur is SO3.
Mass of empirical formula (CH) – 13.02 g/mol
Experimentally determined molar mass of acetylene = 26.04 g/mol = 2.000
mass of empirical formula CH 13.02 g/mol
Percent by mass = 40.68% Cempirical formula = ?
Percent by mass = 5.08% Hmolecular formula = ?
Percent by mass = 54.24% O
10-4 The Formula for a Hydrate
Hydrate: a compound that has a specific number of water molecules bound to its atoms.
In the formula for a hydrate, the number of water molecules associated with each formula unit of the compound is written following a dot.
called sodium carbonate decahydrate
deca- means 10 and hydrate means water
Therefore there are 10 water molecules are associated with one formula unit of the compound.
Mass of hydrated compound = 2.50 g CuSO4·xH2O
Mass of anhydrous compound = 1.59 g CuSO4
Molar mass = 18.02 g/mol H2O
Molar mass = 159.6 g/mol CuSO4
Formula for hydrate = ?
Name of hydrate = ?
Subtract the mass of the anhydrous copper sulfate from the mass of the hydrated copper sulfate to determine the mass of water lost:
mass of hydrates copper sulfate2.50 g
mass of anhydrous copper sulfate - 1.59 g
mass of water lost0.91 g
Calculate the number of moles of H2O and anhydrous CuSO4
1.59 g CuSO4 x 1 mol CuSO4 = 0.00996 mol CuSO4
159.6 g CuSO4
0.91 g H2O x 1 mol H2O = 0.050 mol H2O
18.02 g H2O
Determine the value of x.
x = moles H2O = 0.050 mol H2O = 5.0 mol H2O = 5
moles CuSO4 0.00996 mol CuSO4 1.0 mol CuSO4 1
The ratio of H2O to CuSO4 is 5 : 1, so the formula for the hydrate is CuSO4·5H2O, copper(II) sulfate pentahydrate.