I started lecture today by asking everyone to discuss the following questions:
"Why do we observe a peak in a UV-Vis pattern?"
How did it get there? How can we change its energy? These are the questions we will need to focus on in our research project and they basically boil down to two things: The oxidation state (or # of d electrons on the transition metal) and the overlap of the atomic orbitals interacting to form molecular orbitals.
In order to analyze transition metal complexes you will need to be able to determine the oxidation state and resulting electron configuration of each transition metal cation. When a transition metal forms a complex the d orbitals are lower in energy than the s orbitals and they will always be populated first. So ions, such as Ni2+ have an electron configuration of [Ar] 3d8.
I continued with the MO diagram powerpoint and we observed that when you change the ligand the energy difference between the anti-bonding d orbitals changes, and as a consequence the color changes.
In transition metal complexes two main types of excitations occur. The first is d to d transitions and the second is charge transfer excitations. We will start Monday's class discussing the similarities and differences between these two types of excitations and lead right into the bulk of the material to be covered in the REEL final project. Be sure to read REEL 5 and 6 before Monday's class to give you an edge in understanding the lecture material.
At the end of class there was a pop quiz.
Can you believe that we are half-way through the quarter already?
Friday, April 30, 2010
Wednesday, April 28, 2010
Lecture #14, Wednesday, April 28th
The lecture notes from today's powerpoint lecture are posted on Carmen. Please read over them and play around with the powerpoint so you can see how the molecular orbitals are generated from the orbital overlap of the atomic orbitals. In order to understand the content of your REEL project you will need to have a firm understanding of Molecular Orbital diagrams and how they will relate to a UV-Vis spectrum.
A UV-Vis spectrometer measures the energy at which electronic excitations occur. We can analyze the spectra generated from these instruments in order to rationalize why certain solutions or materials exhibit the colors they do. We will focus on two main factors influencing color: the central transition metal atom and the choice of ligand. Lecture will start up on Friday talking about what happens to the color when we replace one ligand with another, and how we go about arranging the ligands in order of how they split the d orbitals. This is the main topic of REEL Lab 3 and 4. The understanding of this material is vital for your research project so be sure to read over the labs. I know several students expressed frustration that some of this material is not in the book, so in order to help out I plan to post supplemental reading material on Carmen for you to read. In the Content section of Carmen in Section F. titled REEL Supplemental Information I have posted a "chapter" that I wrote on Orbitals, Bonding, MO Diagrams, and Color. Please read through the reading as I hope it will solidify your knowledge on Molecular Orbital Diagrams.
I have also posted pdf versions of all the REEL labs and their report sheets on Carmen. Feel free to read them and start working on them before labs start to get a head start on learning the material.
Song Played Before Class:
Uncle Kracker - Smile
A UV-Vis spectrometer measures the energy at which electronic excitations occur. We can analyze the spectra generated from these instruments in order to rationalize why certain solutions or materials exhibit the colors they do. We will focus on two main factors influencing color: the central transition metal atom and the choice of ligand. Lecture will start up on Friday talking about what happens to the color when we replace one ligand with another, and how we go about arranging the ligands in order of how they split the d orbitals. This is the main topic of REEL Lab 3 and 4. The understanding of this material is vital for your research project so be sure to read over the labs. I know several students expressed frustration that some of this material is not in the book, so in order to help out I plan to post supplemental reading material on Carmen for you to read. In the Content section of Carmen in Section F. titled REEL Supplemental Information I have posted a "chapter" that I wrote on Orbitals, Bonding, MO Diagrams, and Color. Please read through the reading as I hope it will solidify your knowledge on Molecular Orbital Diagrams.
I have also posted pdf versions of all the REEL labs and their report sheets on Carmen. Feel free to read them and start working on them before labs start to get a head start on learning the material.
Song Played Before Class:
Uncle Kracker - Smile
Monday, April 26, 2010
Lecture #13, Monday, April 26th
At the end of lecture on Friday I reviewed some concepts pertaining to molecular orbital theory, which is covered in general chemistry classes at Ohio State in Chapter 9 of the textbook. Here are a few key points you need to consider when you are dealing with molecular orbital theory.
*It's all about the orbital overlap and the electrons residing in the orbitals.
Know the shapes of all the orbitals. If you can't draw the d orbitals like the back of your hand you will fail the 2nd midterm.
Know how to determine the oxidation state and d electron count for the transition metals in transition metal complexes (we will discuss this soon). If you can't do this by the time you get to the 2nd midterm you are in really bad shape.
*The better the orbital overlap the stronger the bond.
*Orbital overlap depends not only whether an orbital is s, p, or d, but also on how those orbitals are oriented in space.
*Before you come to class on Wed, know the shapes of the d orbitals.
*When orbitals of the same phase overlap, they form a bonding interaction which lowers the overall energy of the atomic orbitals interacting making them more stable.
*When orbitals of opposite phases overlap they form an anti-bonding interaction which raises the overall energy of the atomic orbitals interacting, making them less stable
*When you construct a molecular orbital diagram, the total number of all the molecular orbitals must be equal to the sum of all the atomic orbitals. Molecular orbitals can be bonding, anti-bonding, or non-bonding.
Song Played Before Lecture:
Bruce Springsteen - Born To Run
*It's all about the orbital overlap and the electrons residing in the orbitals.
Know the shapes of all the orbitals. If you can't draw the d orbitals like the back of your hand you will fail the 2nd midterm.
Know how to determine the oxidation state and d electron count for the transition metals in transition metal complexes (we will discuss this soon). If you can't do this by the time you get to the 2nd midterm you are in really bad shape.
*The better the orbital overlap the stronger the bond.
*Orbital overlap depends not only whether an orbital is s, p, or d, but also on how those orbitals are oriented in space.
*Before you come to class on Wed, know the shapes of the d orbitals.
*When orbitals of the same phase overlap, they form a bonding interaction which lowers the overall energy of the atomic orbitals interacting making them more stable.
*When orbitals of opposite phases overlap they form an anti-bonding interaction which raises the overall energy of the atomic orbitals interacting, making them less stable
*When you construct a molecular orbital diagram, the total number of all the molecular orbitals must be equal to the sum of all the atomic orbitals. Molecular orbitals can be bonding, anti-bonding, or non-bonding.
Song Played Before Lecture:
Bruce Springsteen - Born To Run
Lecture #12, Friday, April 23rd
The lecture on Friday covered the last few slides of the REEL 1 and 2 content. This is where the cut off is for the content of the first exam. Be sure you know how to work through example problems covering all of this content. Any powerpoint lecture slides are posted on Carmen.
The next unit focuses on color, or more importantly how our eyes detect color. In an atom or molecule electrons reside in orbitals. In an atom the electrons can be found in atomic orbitals, and in a molecule they reside in molecular orbitals. If the energy difference between the highest occupied orbital and the lowest unoccupied orbital falls in the visible region of the electromagnetic spectrum, our eyes will observe color. In class I discussed the relationship between the wavelengths of light these materials absorb and the color we observe with our eyes.
A UV-Vis spectrometer is the instrument we use to collect the absorption spectra for transition metal complexes and we will discuss and interpret them in the REEL labs as well as in class.
Thanks for singing Happy Birthday to me in class.
Song Played Before Lecture:
Trey Songz ft. Fabolous - Say Ahh
The next unit focuses on color, or more importantly how our eyes detect color. In an atom or molecule electrons reside in orbitals. In an atom the electrons can be found in atomic orbitals, and in a molecule they reside in molecular orbitals. If the energy difference between the highest occupied orbital and the lowest unoccupied orbital falls in the visible region of the electromagnetic spectrum, our eyes will observe color. In class I discussed the relationship between the wavelengths of light these materials absorb and the color we observe with our eyes.
A UV-Vis spectrometer is the instrument we use to collect the absorption spectra for transition metal complexes and we will discuss and interpret them in the REEL labs as well as in class.
Thanks for singing Happy Birthday to me in class.
Song Played Before Lecture:
Trey Songz ft. Fabolous - Say Ahh
Wednesday, April 21, 2010
Exam #1 Content
I just finished up putting together the content of the first exam and it is broken down as follows:
Questions #1-15: Solubility
Questions #16-25: XRD, Solids, and REEL Labs #1 & #2
This gives 25 questions worth 7 points each for a total of 175 points. You will be given an hour and eighteen minutes to complete the exam.
The best way to study for these exams is to complete the Solubility and REEL XRD and Solids homework sets. After you have completed these and feel comfortable with the problems you should then go to the appropriate practice exam questions.
Questions #1-15: Solubility
Questions #16-25: XRD, Solids, and REEL Labs #1 & #2
This gives 25 questions worth 7 points each for a total of 175 points. You will be given an hour and eighteen minutes to complete the exam.
The best way to study for these exams is to complete the Solubility and REEL XRD and Solids homework sets. After you have completed these and feel comfortable with the problems you should then go to the appropriate practice exam questions.
Exam #1 Review Sessions
There are two class sections participating in the REEL Pigment Module this quarter. One is my class, and the other is taught by Dr. Ricciardo. Our exams will be practically identical and we have been using the same problem sets and practice exams so attending either review session will be equally beneficial.
Riccirado Review Session: Sunday, April 25th at 7:00 pm in 1008 Evans Lab
Fus Review Session: Monday, April 26th at 8:00 pm in 1000 McPherson
Don't think of the review session as a place to come to learn new material. My review sessions are run solely as a Question/Answer session. If you do not have any questions, the review session will be fairly boring. So come with your questions and hopefully these sessions will help put on the finishing touches to your studying.
Riccirado Review Session: Sunday, April 25th at 7:00 pm in 1008 Evans Lab
Fus Review Session: Monday, April 26th at 8:00 pm in 1000 McPherson
Don't think of the review session as a place to come to learn new material. My review sessions are run solely as a Question/Answer session. If you do not have any questions, the review session will be fairly boring. So come with your questions and hopefully these sessions will help put on the finishing touches to your studying.
Exam #1: Tuesday, April 27th 6:30 pm
Your first Chemistry 123 midterm will be from 6:30 to 7:48pm on Tuesday, April 27th at the following sites:
Room 0021, Lazenby Hall for Laboratory TA's:
Dan Hyatt &
Bryan Sears;
and
Room 0014, University Hall for Laboratory TA's:
Scott Burya,
Yujie Sun &
Amy Tucker.
Room 0021, Lazenby Hall for Laboratory TA's:
Dan Hyatt &
Bryan Sears;
and
Room 0014, University Hall for Laboratory TA's:
Scott Burya,
Yujie Sun &
Amy Tucker.
Lecture #11, Wednesday, April 21st
Today I covered pretty much all of the material up to and including REEL Labs #1 and #2. I still have a few more slides to cover pertaining to phase diagrams, but they should only take a few minutes at the beginning of class. The powerpoint lectures are posted in the content section on Carmen.
The REEL labs seem to have went very well this week with the exception of a few small glitches. I am hoping that from the time you walked into the door to the time you leave the lab you actually have a better grasp of the material. If we can accomplish that then we are doing our job as educators. If we are not accomplishing this please let me know as we will have to make some changes.
The next portion of the material will focus on color in transition metal complexes. We will discuss how our eyes detect color and what excitations are responsible for the color in various complexes such as complex ions and charge transfer salts.
Song Played Before Class:
Kevin Rudolf - I Made It (Ft. Birdman, Jay Sean & Lil Wayne) Cash Money Heroes
The REEL labs seem to have went very well this week with the exception of a few small glitches. I am hoping that from the time you walked into the door to the time you leave the lab you actually have a better grasp of the material. If we can accomplish that then we are doing our job as educators. If we are not accomplishing this please let me know as we will have to make some changes.
The next portion of the material will focus on color in transition metal complexes. We will discuss how our eyes detect color and what excitations are responsible for the color in various complexes such as complex ions and charge transfer salts.
Song Played Before Class:
Kevin Rudolf - I Made It (Ft. Birdman, Jay Sean & Lil Wayne) Cash Money Heroes
Tuesday, April 20, 2010
Lecture #10, Monday, April 19th
Today in class I went into detail about various principles of X-ray diffraction. I used powerpoint and posted the lecture up on Carmen. On Wednesday we will finish up XRD and then cover solid solutions and either at the end of the lecture on Friday/Monday we will cover the next topic in the REEL labs, which will deal with how electronic excitations can be related to color. In order to do that we will review molecular orbital theory.
Quiz #3 Study Guide
The quiz this week will cover fractional/selective precipitation as well as the REEL material you covered this week. The REEL material includes the pre-lab for REEL 5 and the lab you completed this week (1 if you are in 210 CE and 2 if you are in 220 CE).
Friday, April 16, 2010
Lecture #9, Friday, April 16th
Today's lecture was entirely devoted to the content of REEL Lab #1. This lab has three main parts:
A. Lattices and Unit Cells
B. Optical Diffraction
C. X-ray Powder Diffraction
The concept of diffraction is typically introduced in physics classes, but in order to solve the problems we are faced with today, we need to combine concepts from various disciplines. X-ray diffraction is the key tool used by chemists to determine the structures of crystalline solids. To learn a little bit more about the concept of diffraction, check out this youtube link featuring University of Minnesota physics professor Jim Kakalious, who was a science consultant for the Warner Brothers film Watchmen. In Watchman Dr. Manhattan has amazing super powers. Dr. Kakalious outlines which physics phenomena are responsible for these super powers. In the movie Dr. Manhattan can appear in more than one place at once and Kakalious asks how he could possible do this. This can be explained by discussing diffraction. At the 2 min 10 sec mark in the clip diffraction is discussed, which is a signature of the wave phenomena of light.
The one thing I want to emphasize is how on earth can a collection of dots from a diffraction pattern relate to the structure of a solid? Diffraction can tell us the similarities and differences on the slides we used in the optical diffraction part of REEL Lab 1. X-rays can be used to measure the same thing in a crystal structure. Since a bond length is on the Angstrom length scale, we need to use electromagnetic radiation of the same magnitude, or X-rays, to determine the arrangement of atoms in a crystal. In my lectures I have been trying to capture the perspective of the Bragg's as they were trying to determine structures of crystals. I found an article from the research Journal Nature that I posted on Carmen and I think it gives an excellent background for what they were trying to study at the time and will give you a good idea of what to keep in mind as you are performing the labs.
On Monday I will discuss how we can use diffraction to identify the structures of solids and if multiple phases are present in our sample. This is the content of REEL Lab #2.
A. Lattices and Unit Cells
B. Optical Diffraction
C. X-ray Powder Diffraction
The concept of diffraction is typically introduced in physics classes, but in order to solve the problems we are faced with today, we need to combine concepts from various disciplines. X-ray diffraction is the key tool used by chemists to determine the structures of crystalline solids. To learn a little bit more about the concept of diffraction, check out this youtube link featuring University of Minnesota physics professor Jim Kakalious, who was a science consultant for the Warner Brothers film Watchmen. In Watchman Dr. Manhattan has amazing super powers. Dr. Kakalious outlines which physics phenomena are responsible for these super powers. In the movie Dr. Manhattan can appear in more than one place at once and Kakalious asks how he could possible do this. This can be explained by discussing diffraction. At the 2 min 10 sec mark in the clip diffraction is discussed, which is a signature of the wave phenomena of light.
The one thing I want to emphasize is how on earth can a collection of dots from a diffraction pattern relate to the structure of a solid? Diffraction can tell us the similarities and differences on the slides we used in the optical diffraction part of REEL Lab 1. X-rays can be used to measure the same thing in a crystal structure. Since a bond length is on the Angstrom length scale, we need to use electromagnetic radiation of the same magnitude, or X-rays, to determine the arrangement of atoms in a crystal. In my lectures I have been trying to capture the perspective of the Bragg's as they were trying to determine structures of crystals. I found an article from the research Journal Nature that I posted on Carmen and I think it gives an excellent background for what they were trying to study at the time and will give you a good idea of what to keep in mind as you are performing the labs.
On Monday I will discuss how we can use diffraction to identify the structures of solids and if multiple phases are present in our sample. This is the content of REEL Lab #2.
Wednesday, April 14, 2010
USG Elections: April 15-16
I wanted to take a moment to encourage everyone to vote in this year's elections for Undergraduate Student Government, starting Wednesday night at midnight at USG.OSU.EDU. I have done my best to be actively involved in student life, serving as the adviser of various campus clubs/organizations. Through this involvement, I have had the privilege of working with one of the presidential candidates, Jordan Davis, and several of her senatorial candidates on the "Keepin' it Fresh" team. From what I understand, they have the most experience coupled with the most creative and realistic ideas about how to solve the critical problems most Ohio State students face today, such as: improving student safety, expanding career development opportunities, stopping additional mandatory fees, and ensuring that when we transition to semesters no freshmen or sophomores caught in the middle will fall behind. I also know they are serious about developing more tutoring programs on campus and are heavily in favor of creating more research opportunities. You can obtain more specific information about their campaign at voteJORDANandASHLEY.com.
Lecture #8, Wednesday, April 14th
Today the last topic in the solubility unit was covered, which was Fractional/Selective Precipitation. After this topic is covered you should be able to perform all the problems in the solubility homework set and the first exam will mainly be made up of problems similar in nature to that homework set.
The next unit we will cover in class will deal with concepts discussed in the REEL labs. You will be given an incredible opportunity to use advanced instrumentation and investigate relationships requiring critical thinking skills. The only drawback is that this material is not covered in most general chemistry text books, so if you are a student who relies heavily on your text book it may cause some frustration. The REEL lab handouts are designed to contain the material you would typically read from a text (this is one of the reasons the labs are so long).
For Friday's class please try to read through REEL Lab 1, which is titled Diffraction and Crystal Lattices and we will pick up on that material on Friday.
Song Played Before Class:
Kanye West - Amazing ft. Young Jeezy
There's your Kayne Premal :)And if anyone else has requests let me know as I walk through lab.
The next unit we will cover in class will deal with concepts discussed in the REEL labs. You will be given an incredible opportunity to use advanced instrumentation and investigate relationships requiring critical thinking skills. The only drawback is that this material is not covered in most general chemistry text books, so if you are a student who relies heavily on your text book it may cause some frustration. The REEL lab handouts are designed to contain the material you would typically read from a text (this is one of the reasons the labs are so long).
For Friday's class please try to read through REEL Lab 1, which is titled Diffraction and Crystal Lattices and we will pick up on that material on Friday.
Song Played Before Class:
Kanye West - Amazing ft. Young Jeezy
There's your Kayne Premal :)And if anyone else has requests let me know as I walk through lab.
Monday, April 12, 2010
Lecture #7, Monday, April 12th
Today I all but finished up the solubility unit by discussing examples involving the pH effects in the separation of Group II and Group III cations and the "special case" of complex ion formation we refer to as amphoterism.
These two topics are fairly complex, but are very doable after you work through the homework set. Not that we have covered all the factors influencing solubility, you should be able to complete problems 24-57 in the homework set.
At this point the entire solubility homework set can be competed and Quiz II will focus on problems 24-57 and 72-84.
These two topics are fairly complex, but are very doable after you work through the homework set. Not that we have covered all the factors influencing solubility, you should be able to complete problems 24-57 in the homework set.
At this point the entire solubility homework set can be competed and Quiz II will focus on problems 24-57 and 72-84.
Friday, April 9, 2010
Study Habits
On the first day of class I stated that my goals as your professor was to make you a better chemist, a better student, and a better person. Part of being the best student that you can be is to develop good study habits. This week in lab all of you took a quiz. It is shocking to me that only 27 of you took a look at the answer key to the quiz posted on Carmen. Looking at the answer key and working out the problems you got wrong is a vital part of the quiz/exam taking process and it is an integral part of the learning process. It might be a pain in the ass to look these problems over, but just do it!
In order to facilitate this process I will definitely give a "pop quiz" shortly after the first exam to be sure you are looking over the problems the class is having trouble with.
In order to facilitate this process I will definitely give a "pop quiz" shortly after the first exam to be sure you are looking over the problems the class is having trouble with.
Lecture #6, Friday, April 9th
Today I covered two concepts that are arguably the most difficult topics students have in the solubility unit. Complex ion equilibria involve more than one equilibrium expression and tend to take multiple steps to calculate. It is VITAL for the complex ion problems that you get plenty of practice. You need to be able to perform problems 24-46 on the problem set for next week's quiz and you will definitely be responsible for these problems on the exam. Remember that all the problems posted on Carmen are taken from old exams, so this is the best way for you to prepare for the exam.
In addition to the complex ion problem, I covered the equilibrium expressions that allow us to analyze the separation between the Group II and Group III cations. These questions have definitely worked their way into the list of my favorites to ask on exams as they contain concepts learned from multiple sections of this course as well as 122. After today's lecture you should be able to handle questions 72-84 in the homework set and they will definitely show up on the quiz as well.
I hope everyone has a great weekend and I will see you in class on Monday :)
In addition to the complex ion problem, I covered the equilibrium expressions that allow us to analyze the separation between the Group II and Group III cations. These questions have definitely worked their way into the list of my favorites to ask on exams as they contain concepts learned from multiple sections of this course as well as 122. After today's lecture you should be able to handle questions 72-84 in the homework set and they will definitely show up on the quiz as well.
I hope everyone has a great weekend and I will see you in class on Monday :)
Wednesday, April 7, 2010
Lecture #5, Wednesday, April 7th
Lecture started off by continuing with the influence of pH on the solubility of slightly soluble salts. By adjusting the pH, chemists have an excellent way to manipulate the solubility.
If you are asked if HCl (or any other reagent) would increase, decrease, or have no effect on the solubility of say, zinc hydroxide, the very first and most important thing you want to do is WRITE OUT THE SOLUBILITY EQUILIBRIUM. Remember, we are trying to manipulate the equilibrium, so it makes sense to write out the balanced equation first.
The second step is to identify if any of the cations/anions dissolved are acidic or basic. This requires a knowledge of the strong acids and strong bases. Remember from Chem 122 that the conjugate acid of a strong base is neutral and the conjugate base of a strong acid is also neutral. The general rule of thumb is: "The stronger the acid, the weaker the conjugate base and the stronger the base, the weaker the conjugate acid."
To a first approximation we can use Le Chatlier's principle to determine how an equilibrium will shift upon the addition of an acid or base. Acids neutralize bases (lower the hydroxide concentration) and bases neutralize acids (lower the hydrogen ion concentration). This can have a dramatic effect on the molar solubility. The calculations in class showed that at a pH = 7.0, the solubility of zinc hydroxide is 8.9 x 10-7 grams in 4 mL of solution. But if the pH is adjusted to 6.0 then we can dissolve 0.0179 grams of zinc hydroxide in 4 mL of this solution. The take home message here is that pH plays a huge role in the solubility of slightly soluble salts and with this knowledge at our disposal, we can manipulate the solubility equilibrium by adding acidic or basic reagents.
Notice that in the previous paragraph I used the phrase "to a first approximation." Sometimes, based on fundamental principles, things happen that we do not expect. For example if you add concentrated ammonia (a base) to zinc hydroxide, Le Chatlier's principle would predict that the equilibrium will shift to make the zinc hydroxide less soluble. Experimentally, when ammonia is added to zinc hydroxide we observe a large increase in solubility.
Initially this was frustrating to chemists as they tried to come up with a theory for why this was happening. The theory we can use to explain this observation is "complex ion formation." If you have been paying attention you will have heard this term mentioned several times this quarter, but now we will investigate how and why complex ions form.
This opened up a whole new branch of chemistry as complex ions are sometimes referred to as coordination compounds, which involve a transition metal center attached to ligands (surrounding atoms/ions/molecules). This branch of chemistry dealing with transition metal, or coordination complexes, is inorganic chemistry (which is my favorite of all the chemistry subdivisions if you happen to be scoring at home).
We will go over several examples in lecture talking about coordination complexes and how complex ion formation shifts the resulting equilibrium expressions.
If you are asked if HCl (or any other reagent) would increase, decrease, or have no effect on the solubility of say, zinc hydroxide, the very first and most important thing you want to do is WRITE OUT THE SOLUBILITY EQUILIBRIUM. Remember, we are trying to manipulate the equilibrium, so it makes sense to write out the balanced equation first.
The second step is to identify if any of the cations/anions dissolved are acidic or basic. This requires a knowledge of the strong acids and strong bases. Remember from Chem 122 that the conjugate acid of a strong base is neutral and the conjugate base of a strong acid is also neutral. The general rule of thumb is: "The stronger the acid, the weaker the conjugate base and the stronger the base, the weaker the conjugate acid."
To a first approximation we can use Le Chatlier's principle to determine how an equilibrium will shift upon the addition of an acid or base. Acids neutralize bases (lower the hydroxide concentration) and bases neutralize acids (lower the hydrogen ion concentration). This can have a dramatic effect on the molar solubility. The calculations in class showed that at a pH = 7.0, the solubility of zinc hydroxide is 8.9 x 10-7 grams in 4 mL of solution. But if the pH is adjusted to 6.0 then we can dissolve 0.0179 grams of zinc hydroxide in 4 mL of this solution. The take home message here is that pH plays a huge role in the solubility of slightly soluble salts and with this knowledge at our disposal, we can manipulate the solubility equilibrium by adding acidic or basic reagents.
Notice that in the previous paragraph I used the phrase "to a first approximation." Sometimes, based on fundamental principles, things happen that we do not expect. For example if you add concentrated ammonia (a base) to zinc hydroxide, Le Chatlier's principle would predict that the equilibrium will shift to make the zinc hydroxide less soluble. Experimentally, when ammonia is added to zinc hydroxide we observe a large increase in solubility.
Initially this was frustrating to chemists as they tried to come up with a theory for why this was happening. The theory we can use to explain this observation is "complex ion formation." If you have been paying attention you will have heard this term mentioned several times this quarter, but now we will investigate how and why complex ions form.
This opened up a whole new branch of chemistry as complex ions are sometimes referred to as coordination compounds, which involve a transition metal center attached to ligands (surrounding atoms/ions/molecules). This branch of chemistry dealing with transition metal, or coordination complexes, is inorganic chemistry (which is my favorite of all the chemistry subdivisions if you happen to be scoring at home).
We will go over several examples in lecture talking about coordination complexes and how complex ion formation shifts the resulting equilibrium expressions.
Monday, April 5, 2010
Quiz I Study Guide
In preparation for Quiz I, you should know how to perform the following:
*Calculate the Ksp from titration data and know how to do all the example problems from the first two lab periods.
*Given Ksp calculate molar solubility
*Given molar solubility calculate the Ksp
*Convert between molar solubility and the amount in grams that could dissolve in a given volume.
*All the separations from Exp. #25 I discussed in class.
*Know how the Ksp tables relate to the solubility rules and how they are both used to determine if a precipitate will form.
*Know how to predict if a precipitate will form or not form when two reagents are added together.
*Anything from the the notes from Lectures #1-4 will be fair game.
*Be sure you know how to perform the following questions from the solubility homework set: 1-18, 19-22, and 58-71.
*Calculate the Ksp from titration data and know how to do all the example problems from the first two lab periods.
*Given Ksp calculate molar solubility
*Given molar solubility calculate the Ksp
*Convert between molar solubility and the amount in grams that could dissolve in a given volume.
*All the separations from Exp. #25 I discussed in class.
*Know how the Ksp tables relate to the solubility rules and how they are both used to determine if a precipitate will form.
*Know how to predict if a precipitate will form or not form when two reagents are added together.
*Anything from the the notes from Lectures #1-4 will be fair game.
*Be sure you know how to perform the following questions from the solubility homework set: 1-18, 19-22, and 58-71.
Lecture #4, Monday, April 5th
Today I went over the concepts behind the separations in Exp #25 Group I. This content serves two purposes: #1. To get you to understand the concepts behind the lab you are performing, and #2. To set the stage and introduce some concepts such as the common ion effect, which will enable us to manipulate solubility.
After describing the separations from Group I, I calculated the molar solubility of Cd(OH)2 given the amount (in grams) that dissolved per liter. I then used this example to tie into the common ion effect, which directly ties into Le Chatlier's principle to predict the solubility of a slightly soluble salt.
The four main factors influencing solubility that we will look over in class are:
1. Common Ion Effect
2. pH
3. Complex Ion Formation
4. Amphoterism
I did a calculation of the common ion effect today and briefly introduced the strong acids and bases. The following link shows the complete list of strong acids and strong bases. Everything else is weak. You will need to know this list in order to determine how acidic/basic the salts of conjugate acids/bases are. We will start class on Wed. covering how pH influences solubility.
Song played before class:
Rihanna - Umbrella
After describing the separations from Group I, I calculated the molar solubility of Cd(OH)2 given the amount (in grams) that dissolved per liter. I then used this example to tie into the common ion effect, which directly ties into Le Chatlier's principle to predict the solubility of a slightly soluble salt.
The four main factors influencing solubility that we will look over in class are:
1. Common Ion Effect
2. pH
3. Complex Ion Formation
4. Amphoterism
I did a calculation of the common ion effect today and briefly introduced the strong acids and bases. The following link shows the complete list of strong acids and strong bases. Everything else is weak. You will need to know this list in order to determine how acidic/basic the salts of conjugate acids/bases are. We will start class on Wed. covering how pH influences solubility.
Song played before class:
Rihanna - Umbrella
Friday, April 2, 2010
Lecture #3, Friday, April 2nd
Today's class started with me performing a calculation to determine if a particular precipitate will form when you are given the concentrations and volumes of various reagents. Remember that Q can be any concentration you want it to be, and the K, or Ksp, is the concentrations at equilibrium.
I then introduced Qualitative Analysis. A qual. scheme is designed to answer the question "What is present?" The "Clueless" episode from the second season of the hit TV show House, which premiered on the FOX network on March 28, 2006, has a "real world" application of the qualitative analysis scheme. House was certain that his patient was being poisoned by a heavy metal toxin. His intuition tells him that this toxin is gold and he sets out to prove that he is right.
He heads back to his house and grabs a vial of stannous chloride and after he applies the solution to the suspects hands it turns purple, confirming gold is present.
In Experiment #25 you get to act as a "detective" in the same manner House did and will need to identify which cations are present in an unknown sample. You will have four lab periods to identify unknowns from Group I, II, and III. Be sure to read pages 35-37 of the lab manual as it describes how the ions are separated into groups. These grouping are based on solubility, and as I showed in class, to a first approximation we can use the Ksp table to see which ions will precipitate when we add a particular reagent.
I will do my best to explain the fundamental concepts in this lab and relate them to solubility. For instance, Ag+ and Pb2+ are both contained in group I, but Pb2+ is also present in trace amounts in Group II, but Ag+ never is. The reagent used to isolate the Ag+ and Pb2+ ions from the other cations is cold, dilute HCl. I did a calculation relating the Ksp to the molar solubility then calculated the amount of AgCl and PbCl2 that will dissolve in 4 mL of water.
We will discuss more on the experimental conditions of Exp. #25 Group I and introduce the concept of complex ion to start on Monday.
Over the weekend you should be sure to have the Ksp report question quiz finished by 10:00 pm tonight and you should work on the pre-lab for Exp #25.
If you have been keeping up with the material, you should have read sections 17.4, 17.6, 17.7 and you should be able to handle homework questions 1-18, 19-23, and 58-71.
I hope everyone has a Happy Easter!
Songs played before class:
Kenny Chesney - Summertime
Jay Sean - Down (ft. Lil Wayne)
I then introduced Qualitative Analysis. A qual. scheme is designed to answer the question "What is present?" The "Clueless" episode from the second season of the hit TV show House, which premiered on the FOX network on March 28, 2006, has a "real world" application of the qualitative analysis scheme. House was certain that his patient was being poisoned by a heavy metal toxin. His intuition tells him that this toxin is gold and he sets out to prove that he is right.
He heads back to his house and grabs a vial of stannous chloride and after he applies the solution to the suspects hands it turns purple, confirming gold is present.
In Experiment #25 you get to act as a "detective" in the same manner House did and will need to identify which cations are present in an unknown sample. You will have four lab periods to identify unknowns from Group I, II, and III. Be sure to read pages 35-37 of the lab manual as it describes how the ions are separated into groups. These grouping are based on solubility, and as I showed in class, to a first approximation we can use the Ksp table to see which ions will precipitate when we add a particular reagent.
I will do my best to explain the fundamental concepts in this lab and relate them to solubility. For instance, Ag+ and Pb2+ are both contained in group I, but Pb2+ is also present in trace amounts in Group II, but Ag+ never is. The reagent used to isolate the Ag+ and Pb2+ ions from the other cations is cold, dilute HCl. I did a calculation relating the Ksp to the molar solubility then calculated the amount of AgCl and PbCl2 that will dissolve in 4 mL of water.
We will discuss more on the experimental conditions of Exp. #25 Group I and introduce the concept of complex ion to start on Monday.
Over the weekend you should be sure to have the Ksp report question quiz finished by 10:00 pm tonight and you should work on the pre-lab for Exp #25.
If you have been keeping up with the material, you should have read sections 17.4, 17.6, 17.7 and you should be able to handle homework questions 1-18, 19-23, and 58-71.
I hope everyone has a Happy Easter!
Songs played before class:
Kenny Chesney - Summertime
Jay Sean - Down (ft. Lil Wayne)
Thursday, April 1, 2010
Lecture #2, Wednesday, March 31st
Today in lecture I started on our first "unit," which is SOLUBILITY. Solubility was first introduced to us back in Chapter 4 of the textbook and we were only given a chart of "solubility guidelines" telling us if an ionic substance is "soluble" or "insoluble" in aqueous solution. This table is a way to represent solubility in a qualitative sense, but in this course we will look at solubility in a quantitative sense, or we will determine the exact amount of a substance that dissolves.
To determine just how much solute will dissolve in an aqueous solution, chemists can analyze the equilibrium constant, or Ksp. The Ksp is a measure of how much of a solid dissolves to form a saturated solution.
Typically Ksp tables are generated for various inorganic compounds. The chart listed here is shown in the appendix of the lab manual. There is a relationship between these two tables. Focus a minute on the chlorides in the solubility rules table. All chlorides are soluble with the exception of Ag+, Pb2+, and Hg22+ . These are all insoluble, or will form precipitates. All other chlorides will remain in solution. This can now be used as an effective separation technique if we want to isolate Ag+, Pb2+, and Hg22+ from any other cations. This is exactly the case for Exp #25 Group I in the qualitative analysis. If you look at the following figure you can now start to see the relationship between these two tables. If a compound is "insoluble," or more accurately, "slightly soluble" there will be a Ksp value associated with it. The smaller the value for the Ksp, the less soluble a substance is. Let me reiterate that The Ksp is a measure of how much of a solid dissolves to form a saturated solution.
I also discussed Molar Solubility and started class giving you a list of five compounds and asked which one had the largest molar solubility. This is a very common question you will encounter on my quizzes/exams and it will definitely show up on standardized exams such as the MCAT.
Remember that the solubility of a substance is the quantity that dissolves to form a saturated solution, while the the Ksp is the equilibrium constant established and its magnitude can be used to make predictions about solubility. We can directly relate the solubility of compounds with the same ratio of cation:anion, but if two compounds have a different ratio of cation:anion you must perform a calculation using an ICE table in order to predict which compound is more (or less) soluble.
Chemists love the fact that they can predict what will happen in the lab before it even happens. The question we want to ask ourselves now is how can we predict whether a precipitate forms when we add two solutions together? In chemistry 121 the solubility rules were our guide for this, but these guidelines were not very specific about what concentration must be used to facilitate a precipitation reaction. We can selectively separate when various precipitates form by manipulating the concentrations of ions that are mixed together. The reaction quotient, Q, is obtained when concentrations of reactants are inserted into an equilibrium expression. If we are at equilibrium we have a special case of Q that we refer to as K. I performed an example of Q vs. K by analyzing solutions of silver nitrate and potassium chloride.
If you are asked to predict if a precipitate will form you need to calculate Q and compare it to K. In general, if:
Q < K no precipitate forms
Q = K the solution is at equilibrium
Q > K a precipitate will form
We will use these same concepts of solubility to discuss the Qualitative Analysis scheme in Exp. #25 in class on Friday.
I will try my best to keep this blog updated after every lecture and I will post the materials you will be responsible for on the quizzes and exams on here as well. As always I would appreciate any comments or suggestions as to how to make this resource more valuable to you as a student.
To be keeping up with the material up to this point you should do the following:
*Go to Carmen and read the entire syllabus and know what your expectations and responsibilities are for this course.
*Read Section 17.4, 17.6, and 17.7 in the textbook.
*Read pages 35-37 and 39-45 of the lab manual and start working on the pre-lab for Exp #25 Group I.
*Complete problems 1-18 on the solubility homework set.
Song Played Before Class:
The Who: Baba O'Riley
To determine just how much solute will dissolve in an aqueous solution, chemists can analyze the equilibrium constant, or Ksp. The Ksp is a measure of how much of a solid dissolves to form a saturated solution.
Typically Ksp tables are generated for various inorganic compounds. The chart listed here is shown in the appendix of the lab manual. There is a relationship between these two tables. Focus a minute on the chlorides in the solubility rules table. All chlorides are soluble with the exception of Ag+, Pb2+, and Hg22+ . These are all insoluble, or will form precipitates. All other chlorides will remain in solution. This can now be used as an effective separation technique if we want to isolate Ag+, Pb2+, and Hg22+ from any other cations. This is exactly the case for Exp #25 Group I in the qualitative analysis. If you look at the following figure you can now start to see the relationship between these two tables. If a compound is "insoluble," or more accurately, "slightly soluble" there will be a Ksp value associated with it. The smaller the value for the Ksp, the less soluble a substance is. Let me reiterate that The Ksp is a measure of how much of a solid dissolves to form a saturated solution.
I also discussed Molar Solubility and started class giving you a list of five compounds and asked which one had the largest molar solubility. This is a very common question you will encounter on my quizzes/exams and it will definitely show up on standardized exams such as the MCAT.
Remember that the solubility of a substance is the quantity that dissolves to form a saturated solution, while the the Ksp is the equilibrium constant established and its magnitude can be used to make predictions about solubility. We can directly relate the solubility of compounds with the same ratio of cation:anion, but if two compounds have a different ratio of cation:anion you must perform a calculation using an ICE table in order to predict which compound is more (or less) soluble.
Chemists love the fact that they can predict what will happen in the lab before it even happens. The question we want to ask ourselves now is how can we predict whether a precipitate forms when we add two solutions together? In chemistry 121 the solubility rules were our guide for this, but these guidelines were not very specific about what concentration must be used to facilitate a precipitation reaction. We can selectively separate when various precipitates form by manipulating the concentrations of ions that are mixed together. The reaction quotient, Q, is obtained when concentrations of reactants are inserted into an equilibrium expression. If we are at equilibrium we have a special case of Q that we refer to as K. I performed an example of Q vs. K by analyzing solutions of silver nitrate and potassium chloride.
If you are asked to predict if a precipitate will form you need to calculate Q and compare it to K. In general, if:
Q < K no precipitate forms
Q = K the solution is at equilibrium
Q > K a precipitate will form
We will use these same concepts of solubility to discuss the Qualitative Analysis scheme in Exp. #25 in class on Friday.
I will try my best to keep this blog updated after every lecture and I will post the materials you will be responsible for on the quizzes and exams on here as well. As always I would appreciate any comments or suggestions as to how to make this resource more valuable to you as a student.
To be keeping up with the material up to this point you should do the following:
*Go to Carmen and read the entire syllabus and know what your expectations and responsibilities are for this course.
*Read Section 17.4, 17.6, and 17.7 in the textbook.
*Read pages 35-37 and 39-45 of the lab manual and start working on the pre-lab for Exp #25 Group I.
*Complete problems 1-18 on the solubility homework set.
Song Played Before Class:
The Who: Baba O'Riley
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