Blog Entry 2/9/14

This week was another continuation of equilibrium. However, this time we combined a little bit of thermodynamics and what they can tell us about a reaction at equilibrium. We were also introduced to Q, which serves as an indicator of the state of a reaction and what needs to occur in order for that reaction to proceed towards equilibrium.

I’ll admit that equilibrium is not a very solid topic for me, but I can feel myself gain more clarity on the subject each day in class. A few misconceptions about equilibrium were cleared up for me this week. Previously, it was difficult for me to grasp the difference between concentration and rates. I had thought that equilibrium meant that there was an equal amount of products and reactants. However, this is not the case. There could be much more reactants than products at equilibrium or vice versa, and therefore the concentrations could be much different. Equilibrium is when these concentrations stay constant, and the rates of the forward and reverse reactions are the same.

This week was very heavy with emphasis on Le Chatelier’s principle, which states that when stress is placed on a reaction, the reaction proceeds in the direction that counteracts that stress. We continued using ConcepTests that had us think about questions involving Le Chatelier’s principle, and went through various reaction scenarios. Some involved adding a reactant or product, and others involved decreasing or increasing the volume or temperature. As usual, these ConcepTests were very useful for me and helped me understand a few key points regarding equilibrium. They’re actually fun, too, especially when we hear about other classes having heated debates over one question.

We were introduced to RICE tables which serve as an organizing strategy to observe the change in a reaction as it proceeds towards equilibrium.

Dr. J really started to crack down on us this week. In order to further help us understand equilibrium, he had to resort to desperate measures—now we have to turn in our completed lecture worksheets for point! And perhaps even worse, we have started MetaLogs, which serves as a class note-taking strategy for lectures during class. However, although I hate to say it, MetaLogs are quite helpful for me. During our first equilibrium simulation, I felt several “oh, I get it!” moments as I wrote something down on my logs. Putting these thoughts on paper not only gave me examples I could refer back to, it also helped me make some connections that were obscure to me before.

On Friday, we did another simulation involving NO2, a brown gas, and colorless N2O2. We reviewed what it meant when a reaction was endo or exothermic, and then tried to figure out which one the reaction we had was. Having taken in the brown-hued gas into two different syringes, we performed some mini experiments on them. In order to figure out what type of reaction it was, we immersed both syringes into water—one in hot water and one in cold—and observed any changes. The syringe in the hot water became a more concentrated brown, while the syringe in cold water became lighter. Because NO2, the reactant, is a brown gas, this meant that the syringe in hot water contained more reactants. Thus, stress was placed on the products side. The reaction proceeded towards the reactants side to lessen this stress. The “stress” we placed on the system was increasing the temperature, so heat would be placed on the products side. Therefore, this was an exothermic reaction.

We also compressed and expanded the syringes to observe any changes in color. For example, when we compressed the syringe, the gas turned dark immediately, and gradually because lighter once again.

Although equilibrium is a broad and sometimes obscure topic, I can feel myself become more confident with it as we go on and discuss the workings behind it, along with running simulations and working through problems.

Blog Entry 1/19/14

This week in AP chemistry was filled with much more exciting experiments than usual. In class, we performed the experiments many people expect out of a chemistry class: freezing random things, harmlessly setting students’ hands on fire, and freaking out random passerby by pouring suspicious substances near them. On Thursday and Friday, we performed many demos with said suspicious substance: liquid nitrogen! I have to say this was probably one of my favorite weeks in chemistry; learning about a reaction is one thing, but seeing it in action is just plain cool.

We started off the week by completing a few more lecture quizzes on Kinetic Molecular Theory and partial pressures. Recently, we have been starting to participate in ConcepTests as a class much more frequently. Of all the ways we use to go over material in class, I think I’ve found ConcepTests most helpful. Although I find whiteboarding helpful, I sometimes don't have time to finish all of the problems before we go over them, which makes me become confused and a little overwhelmed when we move through each group’s board and their process quickly.

ConcepTests allow for a little more independent thinking. We are given a question on the projector, and asked to think about it and hold up the fingers that correspond to the answer we choose. It’s kind of like a voting system, and it’s very interesting when the class comes up with a broad spectrum of different answers. After voting individually, we discuss the question as a group and agree on one answer. I really like this system because I have to process and solve the question on my own before talking with my group mates. I am able to reach an answer myself without coasting on someone else’s answer and just agreeing with it.

After discussing the question, we go over the question as a class and Dr. J makes sure all of us understand the process used to reach an answer. I don’t ever feel left behind when we use this method, and I feel much more involved in the class.  

The most exciting part of the week was undoubtedly the liquid nitrogen demo. There were many collective “ooohs” and “aaaahs” as we froze objects to our hearts’ desire. We started off with a bouquet of flowers, and went to freezing grapes. We however were not satisfied there, oh no! We continued freezing miscellaneous objects from squash balls to marshmallows. We even froze money! Talk about some pretty cold currency.  I had a frozen marshmallow herself due to my extremely good luck being picked in the Chemistry Volunteer Lottery. Most of my classmates lingered afterwards to try a marshmallow of their own, so of course everyone went home happy.

This demo was not just fun and games, however. We discussed much of the science behind the substances and the behavior of the molecules involved. In one demo, we boiled water by using ice, and little droplets of liquid oxygen condensed on the desk.

The day after we played with something leaning more on the hot side: fire. We bubbled methane over water and some students picked up a handful of large methane bubbles, which were then promptly set on fire by Dr. J. The smell of charred hair might have filled room B403, but it’s not everyday when you get to set your hands on fire and emerge unscathed.

This week in chemistry was a lot of fun, while still being able to be a learning experience. I’m hoping to perform more demos in the future in class!

Blog Entry 12/15/13

This week heralds the return of the AP Chem blogs! Much time has past since we have had to revisit these writing assignments. We have been exploring the topic of enthalpy and entropy (the dreaded “E” word!) and applying them to given scenarios. We started off with discussing our precipitation lab we performed last week. We were given a collection of mystery solutions, and we were to determine the identity of the solutions. We mixed on drop of one solution with a drop of another and observed the reaction; many of them formed precipitates with varying colors. Using our knowledge of net ionic equations and properties of precipitates, we slogged through the reactions and eventually arrived at the correct answers.

Also early in the week, we were introduced to the concept of entropy. The elusive yet dreaded “E-word” had appeared a few times in Tri 1, but this week is when we strove to understand the concept. Using laptops, we completed a lesson online measuring the order of solutions and solutes.

I have confused enthalpy with entropy many times. However, I’ve learned that enthalpy is the measure of energy in the system, while entropy is the measure of randomness or disorder. Admittedly, entropy is still somewhat cloudy of a concept to me; I’m still trying to understand how to connect the disorder of a system with the available microstates of each molecule.

In the middle of the week, we worked out the equation for dissolving sodium acetate trihydrate through the use of standard enthalpies. It takes 36 kJ to perform the reaction, and it is exothermic. We witnessed this reaction when we were given heat packs; after activating them, the pack released 36 kJ of heat, which is what we felt in our hands.

We also started a thermodynamics worksheet involving the calculation of reaction enthalpy values using standard bond enthalpies. We whiteboarded some problems which, as usual, proved very useful to me. The boards did a great job of outlining the steps for finding enthalpy, and many of my classmates asked some good questions, which helped my understanding of the whole process.

We were also introduced to our new lab next week. We aren’t given a procedure, just an objective and a few scraps of information. I’m actually kind of excited for this lab; I enjoy figuring things out even though it may be difficult for me to follow. On Friday, in fact, we worked out the reactions for determining the heat of formation of MgO and the reaction between Mg and HCL. Truthfully, I was having some trouble following the process, but I understood the experiment towards the end through the help of my classmates who were leading the process on the board. I enjoy this challenge, and I’m quite sure 3^rd hour will prevail and win the much sought-after prize: the famed Einstein bagel!

Julien Griffith summons a ball of flame (just kidding, it's just the HCL and Mg reaction)

We also went through questions in the Entropy HotPot. We were to read the question on the screen, and then we held up our fingers indicating which answer we thought was correct. This proved to be inexplicably helpful to me. I really enjoy class discussion, because many people ask questions I myself didn’t know I had. Dr. J explained the process through which we could answer these questions, sometimes by eliminating answers immediately and then using logic to attack a question when we didn’t know the exact answer. I am somewhat apprehensive towards the upcoming exams, but I’m sure the HotPots will prove to be invaluable as a study aid.

Blog Entry 11/10/13

This week in AP Chemistry, we focused on state changes. We started off with some discussion on liquids and solids, and also what it looked like when potassium chloride was dissolved in water. Water is a polar molecule, so when the individual K and Cl ions are broken off, they are surrounded by water molecules and are said to be hydrated. K is a cation, so the water molecules orient themselves so that the more electronegative O atom is pointing towards the ion. For chloride, it’s just the opposite. The partially positive areas of the water molecule, the H atoms, orient themselves so they are pointing towards the chloride anion.

Soap is an everyday necessity. It’s common knowledge that soap is able to clean the grease off of a dish But how does it remove those oils? We discussed this question in class. Soaps are fatty acid chains with hydrocarbon chains. It is a polar molecule, and the hydrophilic part of the chain interacts with water through ion-dipole interactions and hydrogen bonding. The hydrophobic parts curl up into themselves. The chains are attached by dispersion forces and form a spherical surface, which attract the oils and fats on a surface and store them within a sphere.

We also held a brief discussion on why humans aren’t just a mass of liquid or gas by discussing the composition of cell membranes. Cell membranes are made up of phospholipids, a form of fats. These phospholipids form the lipid bilayer, and are composed of a hydrophilic head and hydrophobic tails. Only water and gases can easily pass through this membrane, and large molecules and small polar molecules cannot without the assistance of proteins.

On Tuesday, we whiteboarded what was in the bubbles that come out of boiling water. The bubbles contain water vapor, which is water in its gaseous form. We also went over the IMF and Solids POGIL.

On Friday, we performed a minilab where we were given mystery substances, and based on their properties, we were to decipher which substance it was. The first part of the lab involved testing the electrical conductance of given substances (water, ethanol, acetone, nonane, sodium chloride, steel, and sucrose). We used conductance testers and immersed them in the liquid states of the substances, and also tested the conductance of the dissolved and solid states of the substances. For the substances that weren’t able to be simulated in a certain state (such as molten steel) , we used a QR code to view videos that tested the conductance of these substances. We found that the ionic substance NaCl was an insulator in its solid state, but became a good conductor of electricity when it was dissolved in water.

The second part of the minilab involved observing the properties of different substances and trying to name them. We swirled the liquids to test their viscosity. Glycerin was quite easy to find; it was easily the most viscous due to its three hydroxyl groups. We also tested the evaporation rate and surface tension of the substances, and tried to see if one substance was soluble in another. Acetone evaporated extremely quickly due to its weak intermolecular London dispersion forces.

This lab was very helpful in observing how a molecule’s composition affects its properties. It all depends on the intermolecular forces. The stronger the intermolecular force, the slower a substance will evaporate and the more viscous it will be.

Blog Entry 11/3/13

This week in AP Chemistry, we started off by pondering the effects of the charge and size of an ion on melting and boiling points. We were given a question on the projector screen along with a few choices. Without any discussion with our tablemates, we voted on the choice we found most correct. It was quite similar to the Socrative website we used earlier in the tri. After voting individually, we discussed the question with our tablemates and came up with an answer we all agreed on. Many times, there was a wide variety of answer preference. Other times, however, there was dispute between two choices. I particularly remember having a very engaging discussion about one of the questions, and our table ended up being split in half on what answer we thought was correct. After our table discussion, we saw the correct answer and discussed why the other choices would not have been correct. Coulomb’s law was especially important when thinking of the solution.

The ConcepTest was quite helpful for me, and I hope we do more in the future. The discussions I had with my tablemates really helped me view different ways of approaching a problem, and based on their logic, I often changed my answer when I felt their explanation was more reasonable.

On Tuesday, we started a new POGIL on intermolecular forces. My experience in Latin class already gave me some prerequisite knowledge on the subject, the Latin word “inter” means between, so I assumed that intermolecular forces were forces between molecules. “Intra” means within, and those are the forces within a molecule. We had dealt mostly with intramolecular forces before this week during our covalent bonding unit.

In the middle of the week, we explored why ice is slippery. We all know that it’s difficult to walk on an icy surface without our feet slipping out from underneath us, but we were baffled when asked why this is so. We explored the question at the molecular level by using models of water molecules and simulating the structures of ice and water. When we created the molecular structure of ice, which is a ring-like structure filled with many gaps, it took up a lot of space. This explains why when water is frozen, it expands in the container it is in.

We used our hands to represent the pressure of an ice skater’s blade on the surface of ice. When we pushed down on the ice structure with our hands, the structure collapsed and assumed the structure of water again. Basically, when a skater’s blade makes contact with the ice, the molecules directly under the blade turn into water and cause the ice to be slippery.

Due to catching the nasty cold that has been going around the school, I was unable to attend class on Thursday and Friday. However, I heard we whiteboarded much of the intermolecular forces POGIL and I also stayed caught up by watching the lectures and completing the lecture quizzes. We discussed liquids and solids, and also further discussed intermolecular forces, the strongest of which is hydrogen bonding.