Download mole - CORTEZ

How to Count Atoms
What unit is used to count donuts?
Would that unit be appropriate for counting the # of
people in Jacksonville?
Would it be appropriate for counting # of atoms in a
drop of water?
We need an appropriate unit for counting things that
are too small to see!!
What is mole? Mole Ratio

A Ratio of the Amounts of
Reactants and Products using the
Coefficients of a chemical
reaction.
 Mole is important in Stoichiometry part of
chemistry that studies amounts of substances that are
involved in reaction.
Ex. 1 Cu
(s)
+ 2 AgNO3 (aq) →
2 Ag (s) + Cu(NO3)2(aq)
The Mole Concept:
a.mole- a counting unit, like a dozen, but MUCH larger, a mole
is always equal to Avogadro’s number
b. Avogadro’s # = 6.022 x 1023 = 1 mole
b/c atoms are so small, their counting unit is HUGE!!, a mole
can be used to count anything at the atomic or molecular level
**Avogadro’s # is a conversion factor between moles and
particles**
c. Molar mass- numerically equivalent to amu but in units of
#g/mol, also a conversion factor between grams & moles
Molar Mass
is a mass of one (1) mole of a substance
or any element or compound.
 Mole is a unit of measurement used in
chemistry to express the number of
particles of a substance.
 1 mole = 6.02 x1023 particles

Examples:
 What is the molar mass of Carbon?
 What is the molar mass of Alum inum?
 Compounds: H2O , H2SO4 , CaCl2 . 2H2O
*Mole as a Conversion Factor
 Ex.1 How many particles are in 4.2 moles?
4.2 mol x 6.022x1023part.=
1 mole
2.5x1024 particles
 EX. 2 How many moles are 4.3 x1020 atoms?
4.3x1020 atoms x 1mole =
6.022x1023atoms
7.1x10-4 moles
Mole to Mole Conversion
How many moles of H2O will produced by 4.8 moles
of O2 ?
2C4H10(g) + 13O2 (g) → 8CO2(g) + 10 H2O(g)
1.
 If there are 5.6 moles of Oxygen, how many moles of
CO2 can be produced?
C2H2 (g) + O2 → CO2(g) + H2O(g)
Molar mass and Moles
Problem: You have 16.5 g of oxalic acid, H2C2O4
a. What amount(moles) is represented by 16.5 g of
oxalic acid?
b. How many molecules of oxalic acid are in 16.5 g?
c. How many atoms of carbon are in 16.5 g of oxalic
acid?
Relating Moles to Mass
 Molar Mass of a substance…
1. Is the mass in g of exactly 1 mole
(6.022x1023 particles) of that substance
2. Has the units some # g per 1 mole
Ex. for C 12.011g = 1mole
Means that 1 mole of C weighs 12.011 g
Means that 6.022x1023 atoms of C weigh
12.011 g
3. Is numerically equal to the average atomic
mass but in more useful units, g/mol
4. Is used as a conversion factor
Examples:
• Molar Mass: (Formula Mass)
CuSO4
H2O
MgCl2
Na3PO4
*Molar Mass as a Conversion
Factor
Ex. 1 How much will 7.51 moles of Al weigh?
7.51 mol Al x 26.982 g Al =
1 mol Al
203 g Al
Ex. 2 How many moles are in a 15.2 kg sample of lithium?
15.2 kg x 1000g x 1mole Li =
1 kg 6.94 g Li
2190 mol Li
 How to calculate % Composition?
*find molar mass
*divide mass of the part you are looking for
by molar mass and multiply by 100%
*Ex. %O in H2O?
 Molar mass of H2O is 18 g/mol
 Mass of O in H2O is 16 g
 16 g/18 g * 100% = 88.8%, so water is 88.8%
O
More examples… Percent
Composition
 CO2
 C2H5OH (ethanol)
 NaHSO4
 C2H6
• It is a way to represent a formula
including waters of hydration, which
are water molecules incorporated into
the crystal structure of the salt.
*To find the molar mass of a hydrate
ADD (not multiply) all the waters of
hydration.
Ex. CuSO4●5H2O = 5 waters of hydration
so ADD 5 x 18 (molar mass of water) to
molar mass of CuSO4
Practice

A compound with a mass of 48.72 g is found
to contain 32.69 g of zinc and 16.03 g of
sulfur. What is the percentage composition
of the compound?