Chemical Quantities Review

Stoichiometry Review

What is stoichiometry?

• Calculations that allow you convert between quantities of reactants and products

• Uses Balanced Chemical Equations

Types of stoichiometric calculations

• Mass-Mole conversions of single elements and compound

• Mole-Mole conversions between compounds

• Mole-Mass conversions between compounds

• Mass-Mass conversions between compounds

Mole-Mass and Mass-Mass Converions

• You must know the molar mass of the substance or substances you are interested in

Multiple Choice

Consider an element square on the periodic table.

Which of the following can you use to find molar mass?

• Atomic Number

• Element Symbol

• Element Name

• Atomic Mass

Fill in the Blank

Rhodium is the most expensive metal in the world, trading at over $10,000/oz.

What is the molar mass of rhodium (Rh)?

Molar Mass

• We can also use the atomic mass of elements to determine the molar mass of compounds

• Sum up the masses of each atom in the compound

Molar Mass of Compounds - Example

CO₂

1 Carbon atom = 1 x 12.01 = 12.01

2 Oxygen atoms = 2 x 16.00 = 32.00

Add them together:

12.01 + 32.00 = 44.01 g/mol

Multiple Choice

Baking soda is commonly used in baking to make food (such as bread) rise. The primary ingredient in baking soda is sodium bicarbonate (NaHCO₃).

What is the molar mass of this compound (NaHCO₃)?

• 84.01 g/mol

• 52.01 g/mol

• 107.00 g/mol

• 42.00 g/mol

Molar Mass of Compounds - Example

Ex: (NH₄)₂Se

2 N = 2 x 14.01 = 28.02

8 H = 8 x 1.01 = 8.08

1 Se = 1 x 78.97 = 78.97

Add them together:

28.02 + 8.08 + 78.97 = 65.07 g/mol

Multiple Choice

Calcium nitrate is mainly used as a fertilizer. The compound as the formula Ca(NO₃)₂ .

What is the molar mass of this compound?

• 102.09 g/mol

• 164.10 g/mol

• 70.09 g/mol

• 130.10 g/ol

Poll

How do you feel about calculating molar mass?

• AWESOME! I got this!

• Pretty good.

• Not great. I need another example.

Stochiometric Calculations

Stochiometric calculations are done using dimensional analysis.

General set-up for dimensional analysis problems

Mole-Mass Conversion

What is the mass of 0.75 moles of Ca(NO₃)₂ ?

Open Ended

You want to determine the mass of 3.75 moles of Mg₃N_{2 .}

What is the molar mass of this compound?

Multiple Choice

You want to determine the mass of 3.75 moles of Mg₃N_{2 .}

Which of the following shows the correct set-up for this calculation?

Open Ended

What is the mass of 3.75 moles of Mg₃N₂ ?

(See image for correct set up)

Mass - Mole Conversion

A recipe calls for 3.5 g of baking soda (NaHCO₃). How many moles is this?

Fill in the Blank

A recipe calls for 133 grams of sugar (C₁₂H₂₂O₁₁) and you want to know how many moles this is.

What is the molar mass of sugar (C₁₂H₂₂O₁₁)?

Multiple Choice

A recipe calls for 133 grams of sugar (C₁₂H₂₂O₁₁) and you want to know how many moles this is.

Which of the following shows the correct setup for this calculation?

Fill in the Blank

A recipe calls for 133 grams of sugar (C₁₂H₂₂O₁₁).

How many moles this is?

(see image for correct set-up)

Poll

How do you feel about mole-mass/mass-mole conversions for single compounds?

• AWESOME! I got this!

• Pretty Good.

• Not great. I need another example.

Using a Recipe

A recipe is a set of instructions that you use to make a dish.

5-Ingredient Peanut Butter Chocolate Chip Cookies (Yield = 12 cookies):

- 1 cup peanut butter

- 1 cup brown sugar

- 1 large egg

- 1 tsp baking soda

- 1/2 cup chocolate chips

Suppose you wanted to make 50 cookies. Could you determine how much of each ingredient you would need?

A recipe is a set of instructions that you use to make a dish.

5-Ingredient Peanut Butter Chocolate Chip Cookies (Yield = 12 cookies):

- 1 cup peanut butter

- 1 cup brown sugar

- 1 large egg

- 1 tsp baking soda

- 1/2 cup chocolate chips

Suppose you only had 1/3 cup of brown sugar. Could you determine how much of each ingredient you would need?

How many cookies you could make?

A recipe is a set of instructions that you use to make a dish.

5-Ingredient Peanut Butter Chocolate Chip Cookies (Yield = 12 cookies):

- 1 cup peanut butter

- 1 cup brown sugar

- 1 large egg

- 1 tsp baking soda

- 1/2 cup chocolate chips

Balanced Chemical Equations

• Balanced chemical equations are a "recipe" for a reaction.

• 4 Fe + 3 O₂ → 2 Fe₂O₃

• Coefficients give you mole ratios

• i.e. 4 moles of Iron react with 3 moles of Oxygen Gas and produce 2 moles of Iron (III) Oxide.

What if you want to ....

• Produce more or less product? How much of each reactant would you need?

• Only have a limited amount of a reactant? How much product would you produce? How much of the other reactant would you need?

Mole-Mole Conversions

• Moves between moles of one substance to moles of another substance

• Substance can be a reactant of product

• Uses mole ratios from BLANACED chemical equations.

Multiple Choice

You want to know how many moles O₂ are needed to react with 0.68 moles of Fe.

Which of the following shows the correct set-up for this problem?

(See image for balance equation)

Fill in the Blank

How many moles of O₂ are needed to react with 0.68 moles of Fe?

(See image for correct set-up)

Poll

How do you feel about mole-mole conversions for single compounds?

• AWESOME! I got this!

• Pretty Good.

• Not great. I need another example.