Agriculture ChemistryChapter 10

Measuring Matter

• 3 ways to measure matter– By count 1 dozen apples– By mass 2.0 kg apples– By volume .20 bushels apples

1 dozen apples 2.0kg apples 1 dozen apples

12 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 particles

6.02 x 10^23 representative particle 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 Unknowns

-Mass 1 mol Fe2O3= # 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):