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The!Mad!Lab!

IB Chemistry G12

October 22-29, 2015

10/25/2015

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Housekeeping:  Your chemistry exam has been moved to November 25.  You're simply not ready to take an exam in one week.

In regards to the empirical formula lab, there was simply no way to measure how much oxygen was used due to the fact that we did not have a proper seal on the evaporating dish, and because we had to open it to keep the magnesium ribbon lit, any gas used was lost.  We also lost a fair amount of ash.  I've done the math and there is no way to make it work without doing the lab again, and I'd rather not get caught up in that chicanery any time soon.

I've demonstrated how the calculations should look in your lab report, but you do need to address what went wrong in your Evaluation section.  There is A LOT that went wrong, so your evaluation section will be quite lengthy.

As far as the LR/ER lab, I have completed the calculations that should be included in your lab report.  We had some success with that experiment, so we can begin working on the lab report.  We also need to determine the efficiency of the experiment using percent yield.  Let's decide on a due date for the first draft in about two weeks. The final draft will be due two weeks after that.

Agenda:

1.  Discussion of lab data and report writing.
2.  Determining percent yield.
3.  Introduction to Avogadro's Law & Gases

Lesson Objectives: 
1. Explain the difference between actual yield and theoretical yield.
2. Complete percent yield calculations
3. Explain Avogadro's Law in relation to the behavior of gases.

Content Review: 
Links:  1.3: Reacting Masses & Volumes
Textbook Readings: Section 1.3; p. 33-48

Student Missions:
Mission 1:
Yield, Yield, YIELD!!!  This six-minute vid explains the difference between theoretical, actual and percent yield.
So how do we incorporate this into your LR/ER experiment?  We will first determine the theoretical yield using the amounts we were given.  This is something that will be included in your lab report, so you will be working with different data.  Since we have our experimental (or actual) data, we have our actual yield.  The percent yield is merely a ratio between these two numbers, with the AY as the numerator and the TY as the denominator.  Multiply the result by 100 in order to obtain a percentage.

This describes the efficiency of the reaction.  Percent yields that are at least 80% and up are considered decent.  A PY greater than 90% is good.  Anything lower and the experiment should be run again to increase its efficiency.

How efficient were your reactions?  How would you increase efficiency?  Think about what went wrong or the nature of your equipment.

Practice calculating percent yield.

Mission 2:  That Dude's Back Again. You know, Avogadro.  And this time, he's bringing flatulence into the mix.  By flatulence I mean gas, and by gas I mean the behavior of gases in chemistry.
Avogadro's Law & The Nature of Gases.  Recall that most of a gas' volume is empty space, so its chemical nature is irrelevant to its volume.  The volume of a gas, therefore, is determined by the number of particles, temperature, and pressure.  So if you have equal volumes of gases measured at the same temperature and pressure, it can be assumed that the equal volumes contain an equal number of particles.  This is Avogadro's Law.  Using Avogadro's Law as basis, the volume occupied by one mole of any gas (the molar volume) must be the same for all gases when measured under the same conditions of temperature and pressure.

To determine the number of moles in a gas, divide the given volume by the molar volume. It's similar to molar mass calculations.

At Standard Temperature & Pressure (STP), one mole of a gas has a volume of .0227 cubic meters/mole (22.7 decameters/mol).  Standard temperature is 0 degrees Celsius (273 Kelvin) and standard pressure is 100 kpa (1 atm).

Let's practice playing with gas using this simulation.

Mission 3: Ideally, So To Speak...The ideal gas law is a hypothetical situation where gases behave according to the Kinetic Molecular Theory.  Gas particles move in constant, straight-line motion and do not have intermolecular forces interacting on them, hence the term ideal.  Of course, real gases do not behave ideally, but the IGL is a great starting point for understanding the nature and behavior of non-ideal gases.
Let's practice!!!
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October 18-21, 2015

10/17/2015

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Housekeeping:  Today we're doing two short labs.  I am more concerned about data collection right now.  We will worry about the report later.  These are required practicals, so we must get them done today.

Agenda:

1.  Lab #1: Empirical Formula of magnesium oxide
2.  Lab #2: Limiting & Excess Reactants

Lesson Objectives: 
1.  Calculate the empirical formula of an oxide
1.  Identify the limiting and excess reactants in a chemical reaction.
2.  Calculate percent yield using lab data.

Content Review: 
Links:  1.3: Reacting Masses & Volumes
Textbook Readings: Section 1.3; p. 28-32

Student Missions:
Mission 1:  Empirical Formula of Magnesium Oxide.  
Look on pages 21-22 of the text.  We are going to do this simple experiment.  You need to be able to diagram your setup, which won't be exactly as shown in the text.  We are going to use an alcohol burner instead.  Follow the procedure in the book, but I will provide specific steps for you to include.  There will be a data collection matrix on the board for your use.

Mission 2:  Limiting & Excess Reactants with Zn/HCl.  We will immerse a piece of zinc into a test tube with some hydrochloric acid.  The reaction will run for 2 minutes and then we will measure the amount of products produced using what we've learned about LR/ER.  There will be a data collection matrix on the board.

Homework:  Complete the calculations required for each lab.  Finish filling in the data collection matrix.
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October 13-15, 2015

10/13/2015

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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.
 If Mr. Thornley's video was on #TeamExtra, take a look at this online tutorial from ChemCollective.
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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.
Here's some more practice with percent yield.

10/13 Homework:  Continue working on p. 32, #40-42.
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October 7, 2015

10/6/2015

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Hi girls!  I'll share the bad news first.  I am absent today due to a spider bite.  The good news is that your quiz has been postponed to the next day (October 8), so you have an extra day to study.

Some more practice problems can be found on page 21 (#17-23 odd) and page 27 (#24-34, even) in your textbook.  If you are meeting in PC 12, feel free to BORROW one of my spare textbooks to work on the problems.  Do NOT take the book out of the classroom.  I expect for you to have a strong grasp of the content in sections 1.1 & 1.2.

We will spend no more than 10 minutes reviewing before you take the quiz.  Be sure to bring a calculator.  I will provide a periodic table for your use.  You will not be able to use your notes and the quiz is multiple choice.

Have a great day, ladies!!!
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October 5 - 7, 2015

10/5/2015

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Housekeeping:  Due to King Salman's generosity, things done changed.  Let's look at the updated calendar.  Please show this revised schedule to your parents so that they will have accurate assessment dates.

Lesson Review:  No Socrative today, for obvious reasons.

Agenda:

1.  Demonstration data analysis.
2.  Review for quiz.

Lesson Objectives: 
1.  Analyze lab data and determine if mass was conserved.  Provide explanations as to why or why not.
2.  Understand the content to be covered on the upcoming quiz.

Content Review: 
Weebly Links:  Particulate Nature of Matter & The Mole Concept
Textbook Readings: Section 1.1 & 1.2.

Student Missions:

Mission 1:  About That Lab...?  A long, long time ago, back when dinosaurs walked the Earth and we first started this unit, we did a demonstration with copper and silver nitrate. You collected data on how much copper was used and how much silver nitrate was used. What you needed to find were the products and whether or not mass was conserved.  I do not recall your specific measurements, but I did go back and collect the data on your products.  

Reema: Your experiment produced 0.8mL of copper(II) nitrate and 0.05g of silver.
Reem:  Your experiment produced 0.9mL of copper(II) nitrate and 0.03g of silver.


A simple calculations of conservation of mass  means that you add up the mass of the reactants.  Theoretically, if mass is conserved, the mass of the products should be the same.  But we do not live in a perfect world, so usually the mass of the products is less than the mass of the reactants.  

Determine if mass was conserved in your experiment.

The questions then become: Can you explain why mass wasn't conserved? How would you revise the experiment so that you get more product?  What reactant ran out first and how does this affect the amount of product that was formed?

This leads us into Section 1.3: Reacting Masses & Volumes.  Your quiz over 1.3 will be on October 25, so we have a lot to cover in a short time.  It is my expectation that you will stay on top of the homework and be prepared for the scheduled labs.

Mission 2:  Review.  The quiz over 1.1 & 1.2 is scheduled for Wednesday, October 7.  I have provided for you a practice quiz.  Questions #1-12 cover sections 1.1 & 1.2.  Section 1.3 is covered by #13-20.  Do not work on these just yet, as we will come back to them later.

I will provide the answers below, but you are expected to work on these problems and be prepared with questions if you get some of them wrong.

1. C    2. B    3. D    4. B    5. A    6. C    7. A    8. B    9. D   10. B   11. C  12. B

​10/5 Homework:  Finish the practice quiz.  Additional practice can be found at the end of 1.2 (p. 27) with the problems in the blue box.
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