Agriculture Chemistry

Chapter 10

Measuring Matter

• 3 ways to measure matter – By count – By mass – By volume 1 dozen apples 2.0 kg apples .20 bushels apples 1 dozen apples 12 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 1 st List Knowns and Unknowns 2 nd Always write what you’re given 1 st 3 rd Set up units so they cancel out and the end unit is on the top right 4 th 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 (CH 4 ).

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 SO 3 ?

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: H 2 0 C 6 H 12 O 6 CH 4

You Try It!

1. Find the molar mass of PCl 3 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?

1 st Find Molar mass of NaCl = 58g 2 nd 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 (Fe 2 O 3 ). How many moles of iron(III) oxide are contained in 92.2 g of pure Fe 2 O 3 ?

•

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):