Agenda: 4/21 Objective: To determine quantities needed for chemical reactions in research or manufacturing: Stochiometry Review: Set up of Stoichiometry Problems Graphic Organizer for Stoichiometry Class Practice: Mixed Problems Percent Yield – Practice Problems Mixed Stoichiometry Practice Problems - Pairs 1 Homework: Complete practice problems

2 Essential to Stoichiometry Set-up of problems Given: Amount & Unit Do I need to convert the given to moles? Mole RatioDo I need to convert from moles to another unit? Unknown: Unit The mole ratio is the heart of the stoichiometry calculation

Mole Ratio 3 Mole ratio: Mole Unknown Mole Given Mole ratio: Used the coefficients of a balanced chemical equation

Graphic organizer 4 Mole Ratio Mole________ Mole X Mass Volume of a Gas Particle s 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 RatioDo I need to convert from moles to another unit? Unknown: Unit 5

Putting all the steps together in a stoichiometry calculation Propane (C ₃H₈) reacts with oxygen to produce carbon dioxide and water vapor. Balanced equation: 6

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 RatioDo I need to convert from moles to another unit? Unknown: Unit 7

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 RatioDo I need to convert from moles to another unit? Unknown: Unit 8

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 RatioDo I need to convert from moles to another unit? Unknown: Unit 9 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 RatioDo I need to convert from moles to another unit? Unknown: Unit 10 1 mole of oxygen at STP = ____________ liters

Magnesium reacts with hydrochloric acid to yield magnesium chloride and hydrogen gas. Balanced equation: 11

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 RatioDo I need to convert from moles to another unit? Unknown: Unit 12 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 RatioDo I need to convert from moles to another unit? Unknown: Unit 13 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 RatioDo I need to convert from moles to another unit? Unknown: Unit 14 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. 15

Percent Yield Percent yield: Actual Yield x 100 = % Theoretical Yield In the last stoichiometry problem, grams of sulfuric acid was calculated. However, the sample was weighed and found to be grams. The percent yield is: ______________ x 100 = % Note: the % yield is always less than 100% 16

Percent Yield Calculations 1)Balance this equation and state which of the six types of reaction is taking place: ____ Mg + ____ HNO 3  ____ Mg(NO 3 ) 2 + ____ H 2 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? 17

4)Balance this equation and state what type of reaction is taking place: ____ NaHCO 3  ____ NaOH + ____ CO 2 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? 18

Check answers 1) Balance this equation and state which of the six types of reaction is taking place: 1 Mg + 2 HNO 3  1 Mg(NO 3 ) H 2 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 NaHCO 3  1 NaOH + 1 CO 2 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. 19

Manufacturing Sulfuric Acid Using stoichiometry in an industrial application 20

21 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 H ₂ SO ₄. The company is expecting a shipment of 500 kg of SO ₂ and wants to know how much H ₂ SO ₄ can be made from this shipment.

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

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 SO ₂. 23

Sales If you can sell sulfuric acid for $10 per kg, how much will be the total sales ($)? 24