Intro to Stoichiometry

Composition with Red, Yellow, Blue, and Black

Piet Mondrian

1921

Important Note!

• This presentation is best viewed in presentation mode!

Cookies!!!

• What is required to make chocolate chip cookies (according to the Nestle Toll House recipe)?

Ingredients

• Sugar
• Br. Sugar
• Eggs
• Flour
• Baking soda
• Salt
• Chocolate Chips
• Vanilla
• Butter

​

Ratios Matter!!!!

• 0.75 cp Sugar
• 0.75 cp Br. Sugar
• 2 Eggs
• 2.25 cp Flour
• 1 tsp Baking soda
• 1 tsp Salt
• 16 oz Chocolate Chips
• 1 tsp Vanilla
• 1 cp Butter

​

As an equation

0.75 cp Sugar + 0.75 cp Br. Sugar +

2 Eggs + 2.25 cp Flour +

1 tsp Baking soda + 1 tsp Salt +

16 oz Chocolate Chips + 1 tsp Vanilla +

1 cp Butter → 60 cookies

Application

0.75 cp Sugar + 0.75 cp Br. Sugar + 2 Eggs + 2.25 cp Flour +

1 tsp Baking soda + 1 tsp Salt + 16 oz Chocolate Chips +

1 tsp Vanilla + 1 cp Butter → 60 cookies

​

So how many cookies could you make if you had unlimited ingredients but only 6 eggs? Use dimensional analysis!

6 eggs

x

60 cookies

2 eggs

=

180 cookies

Application

0.75 cp Sugar + 0.75 cp Br. Sugar + 2 Eggs + 2.25 cp Flour +

1 tsp Baking soda + 1 tsp Salt + 16 oz Chocolate Chips +

1 tsp Vanilla + 1 cp Butter → 60 cookies

​

So how much sugar would you use to bake with 6 eggs? Use dimensional analysis!

6 eggs

x

0.75 cp sugar

2 eggs

=

2.25 cp sugar

So in chemistry:

• Let’s look at a chemical equation:

​

CaCO₃(s) + HCl (aq) →

So in chemistry:

• Let’s look at a chemical equation:

​

CaCO₃(s) + 2HCl (aq) → CaCl₂(aq) + H₂CO₃(aq)

Important note:

• H₂CO₃ is called carbonic acid and is quite unstable. When you see it as a product, you need to break it apart into H₂O + CO₂!

So in chemistry:

• Let’s look at a chemical equation:

​

CaCO₃(s) + 2HCl (aq) → CaCl₂(aq) + H₂CO₃(aq)

CaCO₃(s) + 2HCl (aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

​

What does this equation mean?

1 mol CaCO₃ reacts with

2 mol of HCl to produce

1 mol of CaCl₂ and

1 mol of H₂O and

1 mol of CO₂

CaCO₃(s) + 2HCl (aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

​

Mole Ratios!!!!

• The balanced equation gives you mole ratios, not mass (gram) ratios!!!

Let’s practice

How many moles of CO₂ can be produced when 4.5 moles of HCl react in the reaction above?

CaCO₃(s) + 2HCl (aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)

​

4.5 mol HCl

x

1 mol CO₂

2 mol HCl

=

2.3 mol CO₂

Start with given

Use conv factor

Answer with unit, substance, and rounded correctly

New reaction

Predict the products of hydrogen monofluroide reacting with aluminum carbonate. Write the balanced equation.

6 HF + Al₂(CO₃)₃ → 2 AlF₃ + 3 H₂CO₃

​

6 HF + Al₂(CO₃)₃ → 2 AlF₃ + 3 H₂O + 3 CO₂

​

Stoichiometry Practice

How many moles of HF are required to react with 8.29 mol of Al₂(CO₃)₃?

6 HF + Al₂(CO₃)₃ → 2 AlF₃ + 3 H₂O + 3 CO₂

​

8.29 mol Al₂(CO₃)₃

x

6 mol HF

1 mol Al₂(CO₃)₃

=

49.7 mol HF

Start with given

Use conv factor

Answer with unit, substance, and rounded correctly

Stoichiometry Practice

How many moles of AlF₃ can be produced when 33.5 moles of H₂O are produced in the following reaction?

6 HF + Al₂(CO₃)₃ → 2 AlF₃ + 3 H₂O + 3 CO₂

​

33.5 mol H₂O

x

2 mol AlF₃

3 mol H₂O

=

22.3 mol AlF₃

Start with given

Use conv factor

Answer with unit, substance, and rounded correctly

Last practice problem

If 18.9 g of H₂ reacts with excess O₂, what mass of water will be produced?

2 H₂ + O₂ → 2 H₂O

​

​

x

1 mol H₂

2.02 g H₂

x

2 mol H₂O

2 mol H₂

x

18.02 g H₂O

1 mol H₂O

18.9 g H₂

=

169 g H₂O

Start with given

Must conv to mol

Use mol ratio

Conv back to g

Time for Homework!