May 20-24

This week, I learned about endothermic and exothermic reactions. Not only did I learn this, but I also revisited some content from Unit 6 pertaining to the energy bar graphs and even came up with the concept of the transfer of chemical energy through these reactions.

This shows that in the exothermic reaction, the reactants require
more energy to bond than do the reactants in the endothermic
reaction. In the endothermic reaction, the products require more
energy to bond than do the reactants.

But, first, let's first revisit the iron and copper (II) chloride lab. One of the observations I made during the lab was that as the iron nail reacted with the CuCl2, the temperature increased. I knew the temperature was increasing because when I felt the beaker, it felt warmer than previously. Therefore, a chemical reaction occurred in the beaker. Not only this, but energy was also transferred from the aqueous solution to the surface of the glass beaker.

As energy transferred out of the system, the atoms were rearranged. This makes sense because energy was required to break apart the copper and the chlorine. Hence, copper and chlorine were dissociated and formed into neutrally charged ions.

Initially, copper had a charge of +2 while Cl2 had a charge of -1 per chlorine atom. When they were separated, though, the energy transferred to them, dissociating them and transferring electrons. Since the copper has a positive charge (as all metals do), it needed to gain 2 e- (electrons are negatively charged) to neutralize its charge. Hence, the diatomic chlorine lost 2 e-, making it more positive and neutrally charged.

On top, copper is collected on left tube.
On bottom, copper is collected on right tube.

In order to bond the two together, though, they are both put into water in an electrolysis kit to form an aqueous solution. As I've mentioned before, the copper and the chloride separated from each other due to energy. But, where did the energy come from? Obviously, whatever was hooked up to the electrolysis kit! In this case, it was the genecon. The electrons from chloride to copper were transferred from the chloride (right) to the copper (left). In one of the previous, I questioned what would happen if the genecon were turned counter clockwise? It turns out that it doesn't really matter because the electrons are still transferred from the chloride to the copper–just in a counter clockwise direction. Either way, the genecon enabled the electrical current it produced to carry the electrons from one substance to another to neutralize the charges and to separate.

As a result, we came to the conclusion that chemical energy inherently was a major part in this experiment. From this, we learned how to use the LOL diagram charts to graph it. But, the question is how and what would the changes in the ph and th accounts be?

We know that from the experiment with the iron nail and the copper chloride that the iron chloride formed and that the copper precipitate formed. When they reacted, energy escaped the system. But how? When they chemically reacted, a chemical reaction occurred, but of course was used up as soon as all the moles of iron and copper chloride that could possibly react together (of course, the amount is limited depending on the ratios). Hence, after the reaction occurred, chemical energy escaped from the system. The same way worked with thermal energy. As the reaction occurred, the beaker got warmer. Hence, the chemical energy that escaped the system was converted into thermal energy, which of course also was released from the system since the beaker gradually cooled down afterwards.

As I said up top, I would discuss endothermic and exothermic reactions. What occurred here was clearly an exothermic reaction because energy was released from this system. In the reaction, it took more energy to bond together the copper chloride than the iron chloride. Of course, one could say that it took more energy to bond iron and chloride or else they wouldn't be bonded. These both sound plausible, but what is actually happening? Let's considered that in the experiment, there was an excess amount of iron left, which meant that enough energy was used to separate the copper and the chloride and bond the iron to the chloride. Of course, it took more energy to separate the copper and the chloride because it requires more energy to bond than iron chloride. This makes sense because copper has a huger molar mass (63.54 g/mol) than iron (55.85 g/mol). Logically, it would take more energy to take apart something with a greater mass just as much as it would take a greater force (twice as much) to move an object of 200 lbs from x distance and half as much required for the larger object to push the 100 lb object. I noticed a trend that the greater the molar mass, the greater the number of electrons. This would explain why more energy was used to bond copper chloride than iron chloride.

This would also make sense because once the electricity passes through iron, it becomes magnetic, and since less energy is required to bond iron to chloride, this would mean that some of the energy is being used to make it magnetic. However, since some chemical energy has been used up to form a new substance and rearrange the particles, it becomes less magnetic than iron itself.

Therefore, the reactants in an exothermic reaction have greater chemical energy than the energy in the products because some of that energy has already been used up.

This week, however, we have not really looked into endothermic reactions, but endothermic reactions are the opposite. Instead of leaving the system, energy enters the system. This would mean that there was less chemical and thermal energy to begin with, but when the reaction occurred, energy was needed in the system, so the products made required more energy than the reactants. When the alka seltzer is put in the water, for example, a gas is created. But, was it created from the energy that entered the system? This is where it gets confusing. Hopefully, this is something I can put energy into studying next week and for AP Chem next year.

May 13-17

I learned more on not just how to use stoichiometry theoretically but practically as well. This week, my group and I worked on chemically combining iron and copper chloride for this lab.

The challenge was to determine how to balance the equation. Before we proceeded, of course, we massed out the nail to ensure accuracy and then we measured out the required volume of copper chloride. These steps were important to take considering the ratios of the reactants in the balanced equation. If the excess ingredient was, say the iron nail, then this means that some of it is left, which means that too much iron was used; hence, iron would be the excess ingredient. This would make copper chloride the limited reactant was enough of it was used to form the precipitate.

But, the question was what was the precipitate that would form? Initially, I guessed that it would form iron oxide because water was also used in the reaction as well. I figured because of the oxygen in water and my previous experiences with riding my bike in the puddles and leaving my brakes to rust, iron oxide would form.

Hence, the original chemical equation we came up with is:

When the reactants were reacted together, the rust on the nail came right off the nail. This supported my new hypothesis until I realized that the ions in water weren't what separated the iron and the copper chloride because when we performed the fire test (assuming that H2 gas was created, it would combust), nothing happened. Therefore, the water did not react with the iron. So, what did then?
But, my theory before that was even more ridiculous. I believed that the H2 and the Cl2 reacted together to form hydrogen chloride, but hydrogen is one of those weird elements. Even though hydrogen and oxygen are both gases, they can combine to form liquid. Since a liquid has stronger attraction between the particles than a gas, this would disprove my preposterous theory because water has a greater electronegativity than hydrogen chloride. The greater the pull on the electrons is, the greater the attraction is also.

I, was, however, considering that the iron oxidized because the red rust came off the nail, hence I still concluded that the oxygen from water didn't combine with it, but just reacted it with it. This, however, is not a plausible theory because when reactants react with each, they always form a new chemical compound or chemical compounds. Secondly, the copper chloride solution did change color, which is a sign it chemically reacted with something. Initially, the copper chloride was cyan, but when it reacted with the iron, the color changed to a greenish blue to green to greenish red.

Iron (III) Chloride and Iron (II) Chloride

I then noticed that the rust from the nail is the same color as the red solution. Since water wouldn't change the color of the solution (after all, it is colorless) nor the color of copper chloride (since it already turned cyan when it reacted to water), I concluded that it reacted with the iron. But, without the water, the chemical reaction couldn't react between iron and copper chloride because the copper chloride was powdery and the iron was metal. It doesn't make sense to combine both solids together and expect them to form new chemical compounds. The water helped to disassociate the copper chloride and turn it to a liquid so that it could transfer the electrons as it reacted with a positively charged metal. This is what happened when the copper chloride and the iron reacted together.

With this information, I changed the chemical equation and decided that iron chloride formed, and that the precipitate that formed was the copper. I noticed that to start out with, iron was neutrally charged since it wasn't chemically combined to any element and that the copper precipitate that formed was also neutrally charged. Because of this, a single replacement reaction occurred. The iron and the copper swapped places with diatomic chloride.

The stoichiometry was the last step of this lab. The amount of moles for every amount of grams had to be calculated for the reactants. First, let's consider the amount of mass the iron had before hand. Initially, it started out with 30 grams. For every 30 g, there are 0.54 moles since the atomic mass of iron is 55.85 g for every mole. The copper (II) chloride was massed at 7.5 grams. For every 7.5 g, there are 0.06 moles since the atomic mass of copper chloride is 134.45 g for every mole. Based on the ratios of the products (2 FeCl3: 3 Cu) to the reactants (2 Fe: 3CuCl2), 0.04 moles of copper (III) chloride and 0.06 moles of iron are created.

May 6-10

This week was anther continuation of stoichiometry and how to apply it. Last week, I said that stoichiometry can be used to calculate the number of moles of the products will be created based on the ratios and number of moles of the reactants. But, what if there were a limited or excess reactant?

In this case, the same steps can be applied. The only difference is that too much of a product will be left over while not enough or just enough of another product can be used to make the products.

The first step in finding the excess and limited reactants is to know the ratios of the compounds, which can be calculated by balancing the chemical equation.

The second step is to do some mental math. If the ratio of the reactants was 1:3 and the ratio of the actual amount of elements is different from that, then this will affect the yield that will be produced but keep the ratios the same or a different compound will form if the ratios aren't proportionate. For example, if the actual ratio were 1:2, then the larger number of reactants would be used up to maintain the ratio of reactants and to leave the smaller number of reactants left. Since all of 2 would be used up (33% less than 3), 33% of 1 would be used up (leaving 2/3 of the reactant left). The 2/3:2 is equivalent to a 1:3 ratio since 2/3 is 1/3 of 2. By analyzing the changing ratios from the original ratio of compounds to the actual compounds, you can find the excess ingredient as well as the limited reactant.

The above steps are how you solve simple stoichiometry problems. But, complicated ones may involve converting x g of this element to moles. In order to do so, you need to know the molar mass of the element, which can be found on the Periodic Table of Elements, hence making the Periodic Table of Elements quite useful. If you don't see molar mass in the squares, look for atomic mass because the two mean the same thing. The only difference is that atomic mass isn't necessarily attached to moles. It just determines how much mass an element contains. But, the molar mass is associated with the atomic mass per mole (6.02 * 10^23 particles).

Once you have found the molar mass, you can set up a proportion for the molar mass and the given mass of the element. Or, you could divide or multiply the given mass by the molar mass to find the number of moles depending on if the given mass greater than or less than the molar mass. If less than the molar mass, then it must be less than one mole, so you would simply divide the given mass by the molar mass. But, if the given mass is greater than the molar mass, then the molar mass must be divided by the given mass to find the number of moles.

Another complicated process of stoichiometry is if the compound contained more than one element. In this case, add up all the atomic masses together to find the molar mass. Another point to bring up is that molar mass can represent the total atomic mass of the compound whereas the atomic mass represents only one element.

One thing that wasn't mentioned was that stoichiometry only calculates the yield that could be formed. Theoretically speaking, for example, if an experiment involved combining a certain amount of sodium chloride with a certain amount of aluminum sulfate but you have a limited or excess amount of a compound, this will affect the yield you will produce. For example, if you could theoretically produce thrice the amount of sodium sulfate to twice the amount of aluminum chloride using 6NaCl + Al^2(SO4)3 ------- 3Na2(SO4) + 2Al(Cl3) but produced only 200g of sodium sulfate instead of the required 300g, then the yield is about 67%, or a ratio of 2:3. The yield percentage between moles and grams is proportional.

The yield percentage between moles and grams is proportional.

In order to calculate the yield produced, you must go through all the steps of stoichiometry. At the end, once you know the moles of a product produced compared to what could have been produced, you can divide the actual mass or moles of a compound by the theoretical mass or moles. Think of taking a test, and the test consists of 100 questions, but you only get 80% correct. The percentage of questions you got right are 80%. This concept can be applied to find the yield percentage of the products produced.

Mar. 29-Apr.3

This week, I learned about stoichiometry. This is the ratio of chemical reactants and products to one and another. For example, if 2NaCl + CO2 form 2(Na2)O and 1C(Cl2), then the ratios for NaCl to CO2 are 1:1, the ratios for CO2 to (Na2)O are 1:2, etc.

Anyone can say that 1 CO2 + 2 NaCl mean that there is one mole of carbon dioxide while there are two moles of sodium chloride. This, however, can only be true if the molar mass is equivalent to the number of moles (e.g. 1 mole oxygen=16 g). Therefore, it is possible for compounds to have different molar masses, hence number of moles as well.

A good example of this would be with 140 g of CO2 from the above chemical equation. For every 140g, how many moles of CO2 are there? To calculate the molar mass per mole, you must add the atomic masses of each element to each other. Knowing that diatomic oxygen has atomic mass of 32 (16*2) and that carbon has a molar mass of 12.11, you combine 32g to 12.11g to form 44.11 g/mole. But, as stated above, for every 140g of CO2, how many moles are there? To answer this question, set up the molar mass to 140g/X moles as a proportion. The answer is 3.17 moles of CO2. The steps are below:

But, this was, of course, is what we already know. This is just review. Now, let's move on to stoichiometry. In order to represent stoichiometry, we need to know the ratios first in the chemical reaction. Otherwise, if you don't balance the equation, you won't know the ratios, making it only harder to use stoichiometry. Even though it would be possible to still calculate the molar mass of the compounds, you wouldn't be able to identify the quantity of moles.

The next step after balancing the chemical equation is to calculate the molar mass of one of the reactants and find the moles of the other reactant and the products based on the ratios. In order to do so, represent this process using the BCA chart (bottom of the page).

In the problem above, propane is combined with oxygen gas. They yield the products of carbon dioxide and water. To balance the equation, look at the number of carbon in CO2 and propane. In propane, there are three, and in CO2, there is one. In order for this ratio to change from 3:1 to 3:3, there must be 3 CO2. The next step is to look at the hydrogen in propane and water. In propane, there are eight, and in water, there are 4 diatomic hydrogens. In order to keep the same number of hydrogens represented in the formulas and knowing water has diatomic hydrogen, there must be four diatomic hydrogen in order to have the same number of atoms as H8. Since the number of propane didn't have to change, there is only one molecule of propane. With 4 H2, there are four molecules of water. With three carbons, there are three molecules of carbon dioxide.

With one propane and five diatomic oxygen forming three carbon dioxide and four water, we can find the ratios.

However, the last part of the equation to balance is O2. In order to so, count the number of oxygen in water and carbon dioxide and combine them. Since there are three diatomic oxygen in carbon dioxide and 2 O2 (4 O=2 O2), there must have been five diatomic oxygen molecules to start out with.

The last step then is to do the calculations. Since it has been defined that there are 4.17 moles of propane, the moles of the other compounds is in sync with the ratio between propane and the other compounds. For example, propane to 5 O2 is 4.17 to 20.85 (4.17 * 5).

This is my favorite part. Under the before column, write down the number of moles the reactants start out. Then, for the products, write out 0 moles because the reactants haven't chemically combined through a combustion reaction yet. During the change column, this is the change in the number of moles from before to after (e.g. -4.17 moles of propane to represent a loss of moles on the reactant side). Since the moles are combining to form different compounds, the moles of the reactants would be zero in the after column since all the elements were used up with none to spare.

Then, for the products in the change, write the same number, except positive since it gained those moles, not lost them. In the after column, write the number of moles of the products.