Stoichiometry: Mole Ratios

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Stoichiometry: Mole Ratios. October 14 &amp; 15 2013 Ms. Boon Chemistry. Think Box A cookie recipe requires 1 cup of sugar, 2 cups of flour, 1 stick of butter and 3 eggs. How much of each ingredient do you need in order to double the recipe? Explain your answer. Objective:

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### Stoichiometry: Mole Ratios

October 14 & 15 2013

Ms. Boon Chemistry

Think Box

• A cookie recipe requires 1 cup of sugar, 2 cups of flour, 1 stick of butter and 3 eggs.
• How much of each ingredient do you need in order to double the recipe? Explain your answer.

Objective:

I can create mole ratios from a balanced chemical equation and perform mole to mole conversions.

Agenda:

Catalyst

One-Step Stoichiometry Quiz

Notes and Practice: Mole Ratios

Game: Reactants, Products, and Leftovers

Mini Review: What is stoichiometry?

Stoichiometry is the study of the relationships between quantities of substances in chemical reactions.

Where are we going with this?

Next week you will do a lab where you will be asked to answer questions like the one below:

When aluminum foil is dipped in copper (II) chloride a displacement reaction takes place:

2 Al + 3 CuCl2→ 3 Cu + 2 AlCl3

If you dip a 10 g piece of aluminum foil into 20 mL of 0.1 M cupper chloride, how many grams of copper metal will form?

To solve this problem, we need to learn how to use a mole ratio.

Think, Pair, Share: Cookie Recipe Ratios.

A "ratio" is just a comparison between two different things. Look at the cookie recipe in the think box above. List the following ratios as fractions in the space below:

(a) sugar to flour

(b) flour to butter

(c) eggs to butter

(d) eggs to sugar

(e) butter to flour

What is a mole ratio?
• Mole ratios are used to compare the amounts of reactants and products in a balanced chemical reaction equation.
• The coefficients represent the number of moles.
• Mole ratios are conversion factors in stoichiometry problems.

2 Mg + O2 2 MgO

• What is the ratio of moles Mg atoms to moles O2 molecules?
• Write this ratio as a fraction: 2 mol Mg
• 1 mol O2
White Board Practice #1

CH4 + 2 O2 → CO2 + 2 H2O

1 mol CH4

2 mol O2

What is the ratio of moles CH4 to moles O2?

What is the ratio of moles O2 to moles CO2?

What is the ratio of moles H2O to moles CH4?

What is the ratio of moles CO2 to moles H2O?

2 mol O2

1 mol CO2

2 mol H2O

1 mol CH4

1 mol CO2

2 mol H2O

White Board Practice #2

Do the following problem on your white board.

2 NI3 N2 + 3 I2

What is the mole ratio of NI3 to N2?

2) 2 mol NI3

2 mol N2

1) 1 mol NI3

2 mol N2

4) 3 mol NI3

2 mol N2

3) 2 mol NI3

1 mol N2

More White Board Practice

Complete the following problems in your notes.

Give the mole ratio between the two compounds that are in bold red.1) 2FeO + 1 C  2 Fe + 1CO2

2) 2 NO + 1O2 1NO2

3) 1 CH4 + 4S 1 CS2 + 2H2S

Balance the equations and then give the ratio between the two compounds in bold red.

4)__PCl3 +__H2O __H3PO3 +__HCl

5)___Xe + ___F2  ___XeF4

6)__Al +__HCl__AlCl3 +__H2

Mole to Mole Conversion Problems:

In most chemistry lab problems involving stoichiometry, you will know or be able to find out via measurement information about one reactant or product. Based on this information, you will be asked to make calculations to determine the amounts of a different reactant or product. Mole to mole conversions are at the heart of this idea.

Example: You react copper wire with silver nitrate. How much silver nitrate is needed to form 5 g of silver metal as the product?

Mole to Mole Conversions: Example 1

2 Mg + O2 2 MgO

How many moles of MgO can be made from 12 moles of Mg?

Given: 12 mol Mg

Unknown: molMgO

Conversion Factor: 2 molMgO/ 2 mol Mg

Setup & solve:

X

=

12 mol Mg

2 mol MgO

2 mol Mg

12 mol MgO

Mole to Mole Conversions: Example 2

2 Mg + O2 2 MgO

How many moles of Mg are required to produce 8 moles MgO?

Given: 8 molMgO

Unknown: mol Mg

Conversion Factor: 2 mol Mg/ 2 molMgO

Setup & solve:

X

=

8molMgO

2 mol Mg

2 molMgO

8mol Mg

White Board Practice #1

CH4 + 2 O2 → CO2 + 2 H2O

How many moles of CH4 are needed to form 30 moles of H2O?

Given:

Unknown:

Conversion Factor:

Setup & Solve:

X

1 mol CH4

2 mol H2O

=

30 mol H2O

15 mol CH4

White Board Practice #2

Do the following problem in your notes.

2 NI3 N2 + 3 I2

How many moles NI3 are required to produce 10 moles N2?

2) 20 mol NI3

1) 10 mol NI3

4) 40 mol NI3

3) 5 mol NI3

Mole to Mole Conversion Practice

Complete the worksheet problems on your notes.

Work quietly with the people around you.

Tonight’s HW: Read p. 302 – 305; Do practice problems p. 304 #1 & 2, p. 311 #1, 4(a), 6.

Game: Reactants, Products, Left Overs

Work with a partner.

Show work on your white board.

The purpose of the game is to determine the amounts of reactants, products, or left overs based on the given information.