Housekeeping: We will go through your quizzes. I need to put an IB score on it, so make sure you have it ready to give to me. We have a little under two weeks to finish this chapter, so you need to step your game up. Please come to class every day so that you don't get behind.
Agenda:
1. Quiz analysis
2. Section 1.3: Limiting & Excess Reactants
3. Percent yield
Lesson Objectives:
1. Identify the limiting and excess reactants in chemical reactions.
2. Calculate percent yield using mass data.
Content Review:
Links: 1.3: Reacting Masses & Volumes
Textbook Readings: Section 1.3; p. 28-32
Student Missions:
Mission 1: This World Ain't Perfect. Chemical reactions should theoretically go to completion, but they do not because some reactants are used up faster than others. The reactant that runs out first (the limiting reactant or limiting reagent) determines the amount of product that is formed. For example, if you're making cheese sandwiches and you have 16 pieces of bread but five pieces of cheese, but the recipe calls for two pieces of bread and one piece of cheese...how many sandwiches can you make before you run out of ingredients? Which is the limiting ingredient? Which is the excess ingredient (the reactant that is left over)?
Think back to the lab we did before Eid break. I gave you your product mass results and you know that mass wasn't conserved. Which of the reactants do you think ran out first...the silver nitrate or the copper? Usually, the more expensive reactant is the limiting one.
In order to complete LR/ER problems, you need to remember how to read a balanced chemical equation and determine the correct mole ratios. Pages 28-29 cover this, but I won't spend time on it in class because we've already done it. Basically, the mole ratio is key in determining how much product is obtained.
Having said that, here's a quick-N-easy set of guidelines on solving LR problems.
Here's an IB-level video to give you an idea of the math that is involved in understanding the concept. Don't go crazy over doing the problems; we will work those out in class. Just try to understand the concept and get familiar with how to do the work.
Agenda:
1. Quiz analysis
2. Section 1.3: Limiting & Excess Reactants
3. Percent yield
Lesson Objectives:
1. Identify the limiting and excess reactants in chemical reactions.
2. Calculate percent yield using mass data.
Content Review:
Links: 1.3: Reacting Masses & Volumes
Textbook Readings: Section 1.3; p. 28-32
Student Missions:
Mission 1: This World Ain't Perfect. Chemical reactions should theoretically go to completion, but they do not because some reactants are used up faster than others. The reactant that runs out first (the limiting reactant or limiting reagent) determines the amount of product that is formed. For example, if you're making cheese sandwiches and you have 16 pieces of bread but five pieces of cheese, but the recipe calls for two pieces of bread and one piece of cheese...how many sandwiches can you make before you run out of ingredients? Which is the limiting ingredient? Which is the excess ingredient (the reactant that is left over)?
Think back to the lab we did before Eid break. I gave you your product mass results and you know that mass wasn't conserved. Which of the reactants do you think ran out first...the silver nitrate or the copper? Usually, the more expensive reactant is the limiting one.
In order to complete LR/ER problems, you need to remember how to read a balanced chemical equation and determine the correct mole ratios. Pages 28-29 cover this, but I won't spend time on it in class because we've already done it. Basically, the mole ratio is key in determining how much product is obtained.
Having said that, here's a quick-N-easy set of guidelines on solving LR problems.
Here's an IB-level video to give you an idea of the math that is involved in understanding the concept. Don't go crazy over doing the problems; we will work those out in class. Just try to understand the concept and get familiar with how to do the work.
If Mr. Thornley's video was on #TeamExtra, take a look at this online tutorial from ChemCollective.
Practice problems: p. 32 #36-38.
Mission 2: Well How Much Did We Actually Get??? Percent yield is an expression of the efficiency of a reaction. It is based on the theoretical yield (what you're supposed to get) versus experimental yield (what you actually got). The theoretical yield (TY) is usually expressed in grams or moles, and refers to the maximum amount of obtainable product, assuming 100% of the limiting reactant is converted to products. The information comes from the balanced chemical equation.
A summary of the steps are listed on page 31. Mr. Thornley provides a (mercifully) short video showing how to calculate theoretical yields.
Practice problems: p. 32 #36-38.
Mission 2: Well How Much Did We Actually Get??? Percent yield is an expression of the efficiency of a reaction. It is based on the theoretical yield (what you're supposed to get) versus experimental yield (what you actually got). The theoretical yield (TY) is usually expressed in grams or moles, and refers to the maximum amount of obtainable product, assuming 100% of the limiting reactant is converted to products. The information comes from the balanced chemical equation.
A summary of the steps are listed on page 31. Mr. Thornley provides a (mercifully) short video showing how to calculate theoretical yields.
Now we will take it to the next level by determining how to calculate the percent yield using reaction data with this sexy six-minute video from thechemistrysolution.com.