Agriculture Chemistry
Chapter 10
Measuring Matter
• 3 ways to measure matter
– By count
– By mass
– By volume
1 dozen apples
12 apples
1 dozen apples
2.0 kg apples
.20 bushels apples
2.0kg apples
1 dozen apples
1 dozen apples
.20 bushel apples
What is the mass of 90 average-sized apples if 1 dozen of the apples has
the mass of 2.0kg?
Dimensional Analysis
• If .20 bushel is 1 dozen apples and a dozen apples has
the mass of 2.0kg, what is the mass of .50 bushel of
apples?
Dimensional Analysis
• Assume 2.0 kg of apples is 1 dozen and that each apple
has 8 seeds. How many apple seeds are in 14 kg of
apples?
What is a Mole?
•
•
•
To count representative particles in chemistry, we use the mole (mol).
– Representative particles = atoms, molecules, or formula units.
1 mol = 6.02 x 10^23
Called Avagadro’s number = famous dead guy
A mole of ANY substance is 6.02 x 10^23 representative
particles
1 mol
6.02 x 10^23 representative particle
6.02 x 10^23 representative particles
1 mol
Question!!!
• How many representative particles are
in…
A. a mole of water?
B. a mole of Calcium?
C. a mole of sugar?
D. a mole of eggs?
E. a mole of Copper(II) Sulfate?
How large is a mole?
• 1 mole of marshmallows= 18 miles high, covering
Earth’s surface
• 1 mole of dollar bills
to the moon and back 80 billion times
The mass of a mole of an
element
• 1 mole = # C atoms in 12g Carbon (6.02 x 10^23)
• Atomic Mass in grams = mass of 1 mole (6.02 x 10^23 atoms) of the
element.
– Called Molar Mass, measured in grams per mole (g/mol).
• The Molar Mass of any two elements must contain the same # atoms.
– 12.0g Carbon and 16.0g Oxygen have same # atoms. (they just weigh different)
Question: How many atoms are contained in the
molar mass of any element?
What’s the molar mass of…
• Nitrogen
• Phosphorus
• Potassium
Let’s try one!
• Iron is a common metal used in making
agricultural implements. How many moles of Iron
is 1.25 x 10^23 atoms of Iron?
Steps to Success
1st List Knowns and Unknowns
2nd Always write what you’re given 1st
3rd Set up units so they cancel out and the end unit is on the top right
4th Do arithmetic
You try!!!
How many moles is 2.80 x 10^24
atoms of silicon?
How many moles is 2.17 x 10^23
representative particles of
bromine?
Converting Moles to Number of Atoms
Suppose you own a dairy and are curious about the methane emissions from
your cows. You want to know how many atoms are in 2.12 mol of methane
(CH4).
Knowns:
-Number of moles = 2.12 mol CH4
-1 mol CH4 = 6.02 x 10^23 molecules CH4
-1 molecule CH4 = 5 atoms (1 carbon and 4 hydrogen)
-Desired conversion is: moles > molecules > atoms
Unknowns:
-# atoms?
Solve:
You Try
• How many atoms are in 1.14
mol SO3?
Sulfites are used in
wine making and
preserving fruit!
The mass of a mole of a
compound
Add atomic masses of atoms that make up a compound or
molecule.
Find Molar Mass of:
H20
C6H12O6
CH4
You Try It!
1. Find the molar mass of PCl3
2. What is the mass of 1.00 mol of
sodium hydrogen carbonate?
Molar Mass Madness!
• Travel to each station and answer each
problem
• Write down question and answer on piece
of paper
10.2 Mole-Mass and Mole-Volume
Relationships
The Mole-Mass Relationship
• Use molar mass of an element
or compound to convert
between the mass of a
substance and the moles of a
substance.
Example:
• Let’s say you need 3.00 mol of
salt (NaCl) for a recipe. How
do you measure this amount?
1st Find Molar mass of NaCl = 58g
2nd Multiply by a conversion factor
Practice!
•
•
Rust is often a problem in agriculture because it weakens chains or other machinery
made of iron.
When iron is exposed to air, it corrodes to form red-brown rust. Rust is iron(III) oxide
(Fe2O3). How many moles of iron(III) oxide are contained in 92.2 g of pure Fe2O3?
• Knowns
-Mass 1 mol Fe2O3=
Unknowns
# moles?
Try on your own
• Elemental Boron is needed in
alfalfa plants to prevent
stunted growth. In corn, a
boron deficiency results in
twisted ears and barren stocks.
Find the # moles in 3.70 x 10^-1 g
of boron.
Mole-Volume Relationship
• Avagadro’s Hypothesis: equal volumes of gases at the same
temperature and pressure contain equal numbers of particles.
– Particles of different gases are not the same size.
– BUT particles in all gases are so far apart that larger particles don’t need
much more space than the same # or smaller particles.
– Insert Picture Here
– Balloons in room blown up to diff sizes
• Standard temperature and pressure (STP):