Well, OK, I guess it's more over than up...
I have migrated to a new blog address. All the old posts from here were moved over, so they're still available on the new blog. I will not be adding any new posts to this site, all the new ones should be on:
http://chemistryingeneral.blogspot.com/
See you on the new blog, I may still fiddle around with the colors a bit...
2013/02/26
2013/02/23
Keeping track of concentrations
When doing kinetics and equilibrium problems, especially when you're doing an actual hands-on experiment, there are a lot of different concentrations to keep track of. The key to keeping them straight is mostly careful reading and organization, but there are a couple common definitions or descriptions that can help.
Stock Concentration
This is the one that comes up most common in a lab experiment. "Stock" refers to the large samples of reagent from which smaller amounts are taken for individual experiments. When you come to lab, the big bottles or carboys of solution that are on the side benches or in the dispensing hood are "stock" solutions and should have a "stock concentration" listed on the bottle. Most data analysis in lab begins with stock concentrations.
Initial Concentration
In either kinetics or equilibrium problems or experiments, we will often come upon something called an initial concentration. "Initial concentration" is (to me at least) quite fascinating because it's one of those things that we can do on paper that's just not physically possible to do in the real world. The "initial concentration" in a problem or experiment is the concentration of reactants after mixing everything together but before any reaction is allowed to take place. It's as if there was a little "start reaction" button on the side of the beaker, and nothing reacted until we pushed that button. In the real world, as soon as reactant solutions come in contact with each other, they begin to react, so the "initial concentration" is never the actual concentration we might observe in a reaction mixture. The initial concentration is most commonly calculated as a dilution of the stock concentration.
{In some specific reactions, we can probably observe an initial concentration because either the reaction is SO slow that we can mix the reactants before any measurable reaction has occurred, or because there's some external stimulus (like light or heat) required to make the reaction start. These reactions aren't that rare, but they're not reactions that we're likely to use very often in Gen Chem.}
Partial Pressures
When we're working with gases, we can often use Molarity to express the concentration of reactants, but we can also use partial pressures of the gaseous components. Partial pressures are a way to measure the number of moles of a specific gas in a mixture of gases. {Dalton's Law of Partial Pressures} That sounds an awful lot like a concentration... As with the vast majority of data analysis in chemistry, counting moles is the key to figuring out relationships between reacting species. If we know the concentration and volume of a liquid solution, we'll probably be calculating moles at some point. If we know the partial pressure of a gas, we'll probably also be calculating moles at some point. Chemistry is all about the mole!
The most important thing to do when approaching these problems is organization. This is especially true of equilibrium problems; if we can organize the information given in the problem, we'll be much more successful.
Did you hear about the chemist who was thinking very hard about removing excess solvent from a solution? She was concentrating.
Stock Concentration
This is the one that comes up most common in a lab experiment. "Stock" refers to the large samples of reagent from which smaller amounts are taken for individual experiments. When you come to lab, the big bottles or carboys of solution that are on the side benches or in the dispensing hood are "stock" solutions and should have a "stock concentration" listed on the bottle. Most data analysis in lab begins with stock concentrations.
Initial Concentration
In either kinetics or equilibrium problems or experiments, we will often come upon something called an initial concentration. "Initial concentration" is (to me at least) quite fascinating because it's one of those things that we can do on paper that's just not physically possible to do in the real world. The "initial concentration" in a problem or experiment is the concentration of reactants after mixing everything together but before any reaction is allowed to take place. It's as if there was a little "start reaction" button on the side of the beaker, and nothing reacted until we pushed that button. In the real world, as soon as reactant solutions come in contact with each other, they begin to react, so the "initial concentration" is never the actual concentration we might observe in a reaction mixture. The initial concentration is most commonly calculated as a dilution of the stock concentration.
{In some specific reactions, we can probably observe an initial concentration because either the reaction is SO slow that we can mix the reactants before any measurable reaction has occurred, or because there's some external stimulus (like light or heat) required to make the reaction start. These reactions aren't that rare, but they're not reactions that we're likely to use very often in Gen Chem.}
Partial Pressures
When we're working with gases, we can often use Molarity to express the concentration of reactants, but we can also use partial pressures of the gaseous components. Partial pressures are a way to measure the number of moles of a specific gas in a mixture of gases. {Dalton's Law of Partial Pressures} That sounds an awful lot like a concentration... As with the vast majority of data analysis in chemistry, counting moles is the key to figuring out relationships between reacting species. If we know the concentration and volume of a liquid solution, we'll probably be calculating moles at some point. If we know the partial pressure of a gas, we'll probably also be calculating moles at some point. Chemistry is all about the mole!
The most important thing to do when approaching these problems is organization. This is especially true of equilibrium problems; if we can organize the information given in the problem, we'll be much more successful.
Did you hear about the chemist who was thinking very hard about removing excess solvent from a solution? She was concentrating.
Suggested Problems posted
A few people have asked about some suggested end-of-chapter problems from your book. I've picked some from our current chapters (http://www.drbodwin.com/teaching/genchem.php), this should be a good list for you to start with. Use these to identify the areas that you need to study/learn/review a little more, work through additional problems as needed. And always ask questions if you're unsure.
2013/02/16
Gen Chem Pre-Lab poll
For the past few years, I have used video pre-labs (posted on YouTube) as a way to introduce students to the week's experiment in General Chemistry Labs. There were number of reasons for this, and now that I've done it for a while, I'd like to get some feedback. There's a poll on this blog (look left, right above the fish...) to collect your opinions/preferences. If you'd like to leave additional comments, leave them here, that's why I put up a post as well as the poll. I'm not trolling for praise, I really just want to know how useful the video pre-labs are compared to some other options. Setting up, shooting, editing and posting the videos takes a little bit of time and effort, and I kind of enjoy doing it, but if students don't consider it a positive contribution to the lab experience, I could probably re-direct my effort toward other projects.
2013/02/09
Exam manners
I'd like to start by apologizing for my behavior at the end of the exam. I admit that I got a little grumpier than I should have, and I will do my best to never let it happen again. Part of the problem is that I did not make my expectations clear about what I expect when students take exams in my class, so let me try to clarify.
As your instructor, I feel it is my responsibility to provide you the best possible environment in which to take your exams. We take our exams in a large room so that everyone has space. I try to be as quiet as possible while I'm walking around the room. I write time reminders up on the board for those of you who may not be able to see the clock from your seat. I try to provide an environment that is as free from distractions as possible without putting everyone in their own individual, noise-proof rooms.
In return, I expect a few things from you.
1. Arrive on time. It is disruptive to your classmates to have people trickling in, opening and closing doors, plopping down in their seats, and otherwise making noise that is distracting. I understand that there are legitimate reasons for being late, but I doubt that everyone who wandered in late had a good reason. If you KNOW you might be late for a legitimate reason, let me know in advance.
2. Turn OFF your phone. You're not going to answer it during the exam, are you? Many phones vibrate rather loudly when you're in a (hopefully) quiet room, so just turning off the ringer can still be very disruptive to the students sitting near you, trying to concentrate and perform well on the exam.
3. When you finish the exam, either leave or be silent. If there are still people taking the exam and you decide to have a chat with your friend in the exam room, you are being disruptive. In fact, you are being an inconsiderate jerk. In the future, if I hear or see anyone talking in the exam room, I will assume you are trying to cheat in some way and you will fail the course. Even if you've already handed in your exam, I will assume you are trying to cheat and you will fail the course. I understand that many of you have class in SL104 right after our class, so it seems natural to just stay in the room, but if you want to talk to anyone other than me, do it in the hallway.
All of these things can be pretty easily summed up as "Don't do anything that is intentionally disruptive to the other students in the room". That doesn't seem like an unreasonable request to me. I would hope that all of your classmates would behave similarly. If everyone is just a LITTLE considerate of the rest of the people in the room, then EVERYONE can have a more positive and productive exam experience. A couple other tips fall under the "Be prepared and responsible for your own success" category:
1. If you're taking an exam, there's a pretty good chance that you'll need something to write with. I do not use Scantrons for the regular exams in my Gen Chem classes, so it doesn't matter whether you use pencil or pen for regular Gen Chem exams. Pencils and pens are not all that expensive, so it's not a bad idea to have one of each with you. In fact, it's not a bad idea to have 3 or 4 of each with you.
2. If you're feeling a little sniffly or prone to coughing, bring a small pack of tissues and/or some cough drops with to class. {NOTE: If you're using tissues in class, please dispose of them properly. Every semester there's at least one person who throws used tissues on the floor or under their seat in SL104 and the janitors have to clean them up. That's gross. Don't do it.} If your cough or throat tickle is persistent, you might even bring a bottle of water to sip during the exam or class. Speaking of which...
3. Think before you drink. This applies to evening parties, but it's also good advice for early mornings. For most people, if you drink a quart of coffee or soda or juice or water or Red Bull, there's a pretty good chance that all of that liquid will require a stop in a restroom. It's best if this does not occur in the middle of an exam, especially when the exam only lasts 50 minutes. A quick stop in the restroom before the exam starts will let you think about the exam without wondering if your teeth really are literally floating out of your mouth.
4. Bring an appropriate calculator. My calculator policy is in the syllabus and is there thanks to one of your predecessors who downloaded most of the textbook into his TI-84 graphing calculator. In the middle of an exam, I stood looking over his shoulder as he scrolled through the text. I might have a "loaner" calculator with me at the exam, but don't expect it. Similar to the pen/pencil comment above, it wouldn't be the wackiest idea in the world to think about bringing 2 calculators to class, especially since the calculators you are allowed to use on my exams can cost less that $10. I noticed a couple people using extremely basic check-book style calculators during the exam that can't do anything more than add, subtract, multiply and divide. These probably cost $1-2 and would be a GREAT "backup" calculator to have in your bag.
5. Don't ignore the clock. But don't obsess about the clock for the whole 50 minutes. I typically don't audibly announce how much time is left until the 10 minute mark because it's disruptive to students. When I announce "10 minutes left", it means you have some time left to work through a problem or two. When I announce "2 minutes left", that means you might have time to finish the problem you're working on and give a quick look through the exam to make sure your name is on every page and you've answered any multiple choice questions that might be on the exam (even if you have to guess). If I have to announce "30 seconds left", that means you need to get out of your seat and bring me your exam NOW. There is another class waiting to come in the room, and I need to clear out to allow the next class to start on time. I will not come to you and take the exam out of your hands, I will just leave the room and you will earn a score of zero on the exam.
For those of you who have read this far, congratulations, you must actually care about your success in my class and in college and in life. In many cases, you are probably also not the students who really need to read this because you are already considerate of your classmates and doing your best to be prepared and responsible. The vast majority of you are good students, and I thank you for everything you do. You make class better by being there. Have a good weekend and I'll see you on Monday.
As your instructor, I feel it is my responsibility to provide you the best possible environment in which to take your exams. We take our exams in a large room so that everyone has space. I try to be as quiet as possible while I'm walking around the room. I write time reminders up on the board for those of you who may not be able to see the clock from your seat. I try to provide an environment that is as free from distractions as possible without putting everyone in their own individual, noise-proof rooms.
In return, I expect a few things from you.
1. Arrive on time. It is disruptive to your classmates to have people trickling in, opening and closing doors, plopping down in their seats, and otherwise making noise that is distracting. I understand that there are legitimate reasons for being late, but I doubt that everyone who wandered in late had a good reason. If you KNOW you might be late for a legitimate reason, let me know in advance.
2. Turn OFF your phone. You're not going to answer it during the exam, are you? Many phones vibrate rather loudly when you're in a (hopefully) quiet room, so just turning off the ringer can still be very disruptive to the students sitting near you, trying to concentrate and perform well on the exam.
3. When you finish the exam, either leave or be silent. If there are still people taking the exam and you decide to have a chat with your friend in the exam room, you are being disruptive. In fact, you are being an inconsiderate jerk. In the future, if I hear or see anyone talking in the exam room, I will assume you are trying to cheat in some way and you will fail the course. Even if you've already handed in your exam, I will assume you are trying to cheat and you will fail the course. I understand that many of you have class in SL104 right after our class, so it seems natural to just stay in the room, but if you want to talk to anyone other than me, do it in the hallway.
All of these things can be pretty easily summed up as "Don't do anything that is intentionally disruptive to the other students in the room". That doesn't seem like an unreasonable request to me. I would hope that all of your classmates would behave similarly. If everyone is just a LITTLE considerate of the rest of the people in the room, then EVERYONE can have a more positive and productive exam experience. A couple other tips fall under the "Be prepared and responsible for your own success" category:
1. If you're taking an exam, there's a pretty good chance that you'll need something to write with. I do not use Scantrons for the regular exams in my Gen Chem classes, so it doesn't matter whether you use pencil or pen for regular Gen Chem exams. Pencils and pens are not all that expensive, so it's not a bad idea to have one of each with you. In fact, it's not a bad idea to have 3 or 4 of each with you.
2. If you're feeling a little sniffly or prone to coughing, bring a small pack of tissues and/or some cough drops with to class. {NOTE: If you're using tissues in class, please dispose of them properly. Every semester there's at least one person who throws used tissues on the floor or under their seat in SL104 and the janitors have to clean them up. That's gross. Don't do it.} If your cough or throat tickle is persistent, you might even bring a bottle of water to sip during the exam or class. Speaking of which...
3. Think before you drink. This applies to evening parties, but it's also good advice for early mornings. For most people, if you drink a quart of coffee or soda or juice or water or Red Bull, there's a pretty good chance that all of that liquid will require a stop in a restroom. It's best if this does not occur in the middle of an exam, especially when the exam only lasts 50 minutes. A quick stop in the restroom before the exam starts will let you think about the exam without wondering if your teeth really are literally floating out of your mouth.
4. Bring an appropriate calculator. My calculator policy is in the syllabus and is there thanks to one of your predecessors who downloaded most of the textbook into his TI-84 graphing calculator. In the middle of an exam, I stood looking over his shoulder as he scrolled through the text. I might have a "loaner" calculator with me at the exam, but don't expect it. Similar to the pen/pencil comment above, it wouldn't be the wackiest idea in the world to think about bringing 2 calculators to class, especially since the calculators you are allowed to use on my exams can cost less that $10. I noticed a couple people using extremely basic check-book style calculators during the exam that can't do anything more than add, subtract, multiply and divide. These probably cost $1-2 and would be a GREAT "backup" calculator to have in your bag.
5. Don't ignore the clock. But don't obsess about the clock for the whole 50 minutes. I typically don't audibly announce how much time is left until the 10 minute mark because it's disruptive to students. When I announce "10 minutes left", it means you have some time left to work through a problem or two. When I announce "2 minutes left", that means you might have time to finish the problem you're working on and give a quick look through the exam to make sure your name is on every page and you've answered any multiple choice questions that might be on the exam (even if you have to guess). If I have to announce "30 seconds left", that means you need to get out of your seat and bring me your exam NOW. There is another class waiting to come in the room, and I need to clear out to allow the next class to start on time. I will not come to you and take the exam out of your hands, I will just leave the room and you will earn a score of zero on the exam.
For those of you who have read this far, congratulations, you must actually care about your success in my class and in college and in life. In many cases, you are probably also not the students who really need to read this because you are already considerate of your classmates and doing your best to be prepared and responsible. The vast majority of you are good students, and I thank you for everything you do. You make class better by being there. Have a good weekend and I'll see you on Monday.
2013/02/07
Improving your lab scores
A few trends are emerging that are causing people to lose points in lab.Hopefully this will help.
Pre-Lab Quizzes:
1. Do them. One of the fastest ways to fail Gen Chem lab is to skip quizzes.
2. Look at them early enough to ask questions. Pre-lab quizzes are due by 8:00am on Thursdays this semester. If you email me a question at 11:45pm on Wednesday night, I will not see it or answer it in time to be helpful for you. Please do not interpret this as "Don't ask questions." I WANT you to ask questions if you don't understand a problem, but it's more effective to ask those questions on Monday or Tuesday.
3. Read the questions carefully. This actually applies to any situation in any class. There are ALWAYS little clues in the way a question is asked. They may be subtle at times, but they're there. For example, "assume volumes are additive" probably means that you might have to add some volumes together at some point. There may be times that I include information that is NOT necessary to solve a problem, but I definitely don't go out of my way to put a bunch of non-essential information in a problem, especially when it's an online quiz question.
Hand-In Assignments:
1. Circle, highlight, or otherwise clearly indicate who your Lab Assistant is on everything. When I'm trying to sort 100+ assignments, it's much easier if you've obviously done this. On future assignments, if you do not clearly and obviously indicate your Lab Assistant, you will lose points.
2. All assignments must be typed. This includes sample calculations. There are only 2 (maybe) exceptions to this: experimental set-up diagrams in lab reports, and questions that ask you to label things on a printed graph. In both of these cases, it would be BETTER to do everything electronically so you have a back-up copy to print. ("I lost my only copy of the graph as I was walking to Hagen to hand in my assignment 5 minutes before it was due.") If you don't know how to use an equation editor in MSWord or other word processing programs, look into it. They're great tools and can make really nice looking sample calculations.
3. Read the questions carefully and answer them completely. If your answer to a question takes fewer words than the actual question, you're probably not answering the question completely. Especially in lab, there are very few questions that have "Yes" or "No" as an answer. Always explain at least a little bit why the answer is "Yes" or "No".
Look back through old posts on this blog; this isn't the first time I've posted tips on how to improve scores. Use the resources you have available to you.
Pre-Lab Quizzes:
1. Do them. One of the fastest ways to fail Gen Chem lab is to skip quizzes.
2. Look at them early enough to ask questions. Pre-lab quizzes are due by 8:00am on Thursdays this semester. If you email me a question at 11:45pm on Wednesday night, I will not see it or answer it in time to be helpful for you. Please do not interpret this as "Don't ask questions." I WANT you to ask questions if you don't understand a problem, but it's more effective to ask those questions on Monday or Tuesday.
3. Read the questions carefully. This actually applies to any situation in any class. There are ALWAYS little clues in the way a question is asked. They may be subtle at times, but they're there. For example, "assume volumes are additive" probably means that you might have to add some volumes together at some point. There may be times that I include information that is NOT necessary to solve a problem, but I definitely don't go out of my way to put a bunch of non-essential information in a problem, especially when it's an online quiz question.
Hand-In Assignments:
1. Circle, highlight, or otherwise clearly indicate who your Lab Assistant is on everything. When I'm trying to sort 100+ assignments, it's much easier if you've obviously done this. On future assignments, if you do not clearly and obviously indicate your Lab Assistant, you will lose points.
2. All assignments must be typed. This includes sample calculations. There are only 2 (maybe) exceptions to this: experimental set-up diagrams in lab reports, and questions that ask you to label things on a printed graph. In both of these cases, it would be BETTER to do everything electronically so you have a back-up copy to print. ("I lost my only copy of the graph as I was walking to Hagen to hand in my assignment 5 minutes before it was due.") If you don't know how to use an equation editor in MSWord or other word processing programs, look into it. They're great tools and can make really nice looking sample calculations.
3. Read the questions carefully and answer them completely. If your answer to a question takes fewer words than the actual question, you're probably not answering the question completely. Especially in lab, there are very few questions that have "Yes" or "No" as an answer. Always explain at least a little bit why the answer is "Yes" or "No".
Look back through old posts on this blog; this isn't the first time I've posted tips on how to improve scores. Use the resources you have available to you.
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