Moles and Stoichiometry

Chapters 11 & 12

Counting Particles

Particles are counted in moles Types of representative particles

• Atoms- smallest unit of an element

• Molecule- smallest unit of a molecular compound

• Formula Unit- smallest unit of an ionic compound

What is a Mole?

1 dozen = 12 of anything

1 gross = 144 of anything

1 ream = 500 of anything

1 mole = 6.02 x 1023 of anything

Why?

Atoms are inconceivably small

Avogadro’s Number- 6.02 x 1023 is the number of carbon-12 atoms in 12g

Understanding Reactions

N2 + 3H2 2NH3

1 molecule of nitrogen and 3 molecules of hydrogen produce 2 molecules of ammonia

1 mole of nitrogen molecules and 3 moles of hydrogen molecules produce 2 moles of ammonia molecules

Counting Particles

Moles → Particles (multiply by Avogadro’s number)• Example: how many atoms are there in 3

moles of aluminum?

Particles → Moles (divide by AN)• Example: How many moles are there in

5.71x1027 formula units of calcium chloride?

Mass and the Mole

MM (molar mass)- mass of 1 mole of representative particles in a compound or element

Converting Between Moles and Grams• Grams → Moles (divide by molar mass)

• Example: How many moles are there in 135.2 g of water?

• Moles → Grams (multiply by MM)

• Example: How many grams are there in 3.46 moles of calcium carbonate?

Chapter 12- Stoichiometry

Stoichiometry- using chemical formulas to determine molar and mass relationships from balanced chemical equations

The Mole Ratio

All Roads go Through Moles

Calculations between mass and particles are possible by first calculating the number of moles

Percent by Mass (Percent Composition)

Remember? What is the percent composition of each

element in sodium phosphate?

Determining an Empirical Formula

Empirical Formula- lowest whole number ratio of elements in a compound• Use % composition and assume 100g

• Divide by MM of each element to get moles

• Divide all by lowest number of moles

• Multiply to get the lowest whole number ratio

• Record empirical formula

Example: a compound is determined to be 36.4% nitrogen and 63.16% oxygen, what is the empirical formula?

Determining a Molecular Formula

Molecular Formula- multiple of empirical formula that accurately shows number of each atom• Calculate mass of empirical formula (EFM)

• Divide MM of the compound by the EFM

• Multiply empirical formula by result

• Record molecular formula

Example: A compound has a molar mass of 110.0 g/mol. What is the molecular formula if it is 65.45% C, 5.45% H, and 29.09% O?

Practice

1. Sulfuric acid reacts with sodium hydroxide in a double replacement reaction. If you start with 5.25 moles of NaOH, how many moles of water can you make?

2. If you start with 11.34 grams of NaOH, how many moles of sodium sulfate can you make?

3. If you start with 55.1 grams of NaOH, how many grams of sodium sulfate can you produce?

The End of a Long Road...

Limiting Reagents Percent Yield