Agenda: 4/21Objective: To determine quantities needed for chemical

reactions in research or manufacturing: Stochiometry

Review: Set up of Stoichiometry ProblemsGraphic Organizer for Stoichiometry Class Practice: Mixed Problems

Percent Yield – Practice Problems

Mixed Stoichiometry Practice Problems - Pairs

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Homework: Complete practice problems

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Essential to Stoichiometry Set-up of problems

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

The mole ratio is the heart of the stoichiometry calculation

Mole Ratio

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Mole ratio: Mole Unknown Mole Given

Mole ratio: Used the coefficients of a balanced chemical equation

Graphic organizer

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Mole Ratio

Mole________Mole Mole Mol

eX

Mass Volume of a Gas

Particles

Volume of a Gas

Mass

Particles

Putting all the steps together in a stoichiometry calculation

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Putting all the steps together in a stoichiometry calculation

• Propane (C₃H₈) reacts with oxygen to produce carbon dioxide and water vapor.

• Balanced equation:

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Example 1:

• How many moles of oxygen are required to completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Example 1: • How many moles of oxygen are required to

completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Example 2: • How many grams of oxygen are required to

completely react 10 moles of propane?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Molar mass of oxygen:

Example 3:

• How many liters of oxygen are required to completely react 10 moles of propane? Given:

Amount & Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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1 mole of oxygen at STP = ____________ liters

Magnesium reacts with hydrochloric acid to yield magnesium chloride and

hydrogen gas.

• Balanced equation:

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Example 4: • How many moles of magnesium chloride will be produced if a

chemist starts with 120 grams of magnesium metal and plenty* of hydrochloric acid?

*Chemistry language: “with an excess of hydrochloric acid”

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Molar mass of magnesium:

Example 5: • How many grams of magnesium chloride will be produced if a

chemist starts with 60 grams of magnesium metal and an excess of hydrochloric acid?

Given: Amount &

Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Molar mass of magnesium: Molar mass of magnesium chloride:

Example 6: • How many liters of Hydrogen gas will be produced

with 60 grams of hydrochloric acid and an excess of magnesium? Given:

Amount & Unit

Do I need to convert the

given to moles?

Mole Ratio Do I need to convert from

moles to another unit?

Unknown:Unit

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Molar mass of hydrochloric acid: 1 mole of hydrogen gas at STP:

Percent Yield

• Stoichiometry calculations always give the maximum amount that can be produced.This is called the _________ ________.

• In real life, the maximum amount is never produced. Reactions do not proceed perfectly. The _________ ________

is produced.

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Percent Yield

• Percent yield: Actual Yield x 100 = % Theoretical Yield

• In the last stoichiometry problem, 661.5 grams of sulfuric acid was calculated. However, the sample was weighed and found to

be 650.7 grams. The percent yield is: ______________ x 100 = %

Note: the % yield is always less than 100%

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Percent Yield Calculations

1)Balance this equation and state which of the six types of reaction is taking place: ____ Mg + ____ HNO3 ____ Mg(NO3)2 + ____ H2

Type of reaction: __________________________ 2)If I start this reaction with 40 grams of magnesium and an excess of nitric acid, how many grams of hydrogen gas will I produce? 3)If 1.7 grams of hydrogen is actually produced, what was my percent yield of hydrogen?

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4)Balance this equation and state what type of reaction is taking place: ____ NaHCO3 ____ NaOH + ____ CO2

Type of reaction: __________________________ 5) If 25 grams of carbon dioxide gas is produced in this reaction, how many grams of sodium hydroxide should be produced? 6) If 50 grams of sodium hydroxide are actually produced, what was my percent yield?

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Check answers1) Balance this equation and state which of the six types of reaction is taking place: 1 Mg + 2 HNO3 1 Mg(NO3)2 + 1 H2 Type of reaction: single displacement 2) If I start this reaction with 40 grams of magnesium and an excess of nitric acid, how many grams of hydrogen gas will I produce?3.3 grams (when Mg atomic mass = 24.3 grams) 3) If 1.7 grams of hydrogen is actually produced, what was my percent yield of hydrogen? 52%

4)Balance this equation and state what type of reaction is taking place: 1 NaHCO3 1 NaOH + 1 CO2 Type of reaction: decomposition 5) If 25 grams of carbon dioxide gas is produced in this reaction, how many grams of sodium hydroxide should be produced?

22.7 grams NaOH 6)If 50 grams of sodium hydroxide are actually produced, what was my percent yield?

50/22.7 x 100% = 220%Hopefully, you understand that this is not a reasonable answer to this question and indicates that something very wrong happened during this reaction.

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Manufacturing Sulfuric Acid

Using stoichiometry in an industrial application

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Here is a typical problem:• Sulfuric acid, an important chemical in

industry, is manufactured and sold by XYZ company.

• Sulfur dioxide gas is combined with water and oxygen to make H₂SO₄.

• The company is expecting a shipment of 500 kg of SO₂ and wants to know how much H₂SO₄ can be made from this shipment.

What are the steps to determine the amount of sulfuric acid?

1.

2.

3.

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Determining sales value

• They can then calculate how much money they will make from the sale of their sulfuric acid.

• Water and oxygen are readily available and cheap, so the company uses an EXCESS of these substances, which means they use more than enough to react with the SO₂.

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Sales

• If you can sell sulfuric acid for $10 per kg, how much will be the total sales ($)?

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