SG Chem 2A Week 8 blog

The past week and a half in SG chemistry has consisted of Labs and also the new concept of equaling out chemical equations. To start the unit we did the nail lab that spanned three days in class as well as a weekend in between. In this lab our purpose was to determine the ratio of copper produced to iron consumed in a replacement reaction. We did this in the separation of copper(II) chloride dihydrate into a solid copper substance, water and chlorine gas. This lab was really great to do at the beginning of the unit so that we could see what we were going to be studying, which is chemical reactions. It also gave me a feel for what a real chemist does in the field, and it is very exciting to see that these reactions are more than just what is on a piece of paper.

The first step in this lab was to take the dehydrated copper(II) chloride and dissolve it in water. It was very cool to observe as it dissolved because it went from green to blue. Something I did not know before this lab was that color change indicates a chemical reaction. I'm curious to discover what kind of reaction it is. We then put iron nails inside the solution and let them sit for overnight. In the photo below you can see how the copper already started condensing around the nails even after first putting them in.

When we came back to class the next day, the solution looked like this.

The copper in the chlorine has separated, with the copper condensing around the iron nails, and the chlorine having evaporated into the air. This leaving mostly water as the liquid. We noticed the liquid was now mostly yellow and I still wonder why all of these color changes took place. We drained the solution leaving the copper behind and rinsed it with deionized water and got what you see below.

What you see below is the copper after it had been dried over the weekend.

After the lab part of this was done it was on to the calculations. After receiving all of our masses and doing the calculations to find the moles of iron and copper we determined that they were at a one to one ratio, and I interpreted this as one atom of iron bonds with one atom of copper.

This lab was very interesting and useful for me because I got to apply what I have been learning the whole trimester. It also really help me visualize the equation and understand what is happening when we write out a chemical reaction. This is especially helped me as we continued into the next concept of balancing equations.

The bulk of the next week was focused on practice in balancing equations. I mostly understood this concept, except what mostly confuses me is when an equation contains polyatomic ions and you have to balance them on each side. I also need more practice with when you have to use mixed fractions and then multiply the entire equation. Aside from this I am good at visualizing the atoms in the equation and understanding what happens in the process.

I really enjoyed the series of labs we did in the middle of the week also. There were 10 different Labs at different stations and we got to experience five different types of reactions; combination reactions, decomposition reactions, single replacement reactions, double replacement reactions and combustion reactions. I again really enjoyed being able to see the chemistry at work because usually we just see it on a piece of paper. I'm looking forward to learning more about these reactions and I'm wondering specifically what these different types of reactions entail, and being able to distinguish them from one another.

SG Chemistry 2A Week 7 Blog

To start this week off with a fun activity, Dr. Finnan did two demonstrations for us. For the first demonstration, as shown on the left, he took a copper sheet and used a burner on it. It was very interesting to observe as the copper turned black where it was being heated. He then turned it around and heated the other side, and everyone was fascinated as the color turned back to the state before it was burned. This, as he explained, was due the electrons jumping from the heat and the charge of copper. The next demonstration was a magnesium and oxygen reaction. As shown in the picture, the substance burned very brightly and was fascinating to watch. These activities moved us into our next unit of naming compounds, and the difference between ionic and molecular compounds.

This was a very useful unit for me in which I learned a lot, and made things a lot easier when explaining so that I didn't have to say awkward letters instead of the correct names of the compounds. To begin the unit we worked on a POGIL called naming ionic compounds. With this worksheet we worked together in table groups and discovered that ions have charges: either positive, cation, or negative, anion. We weren't sure what causes these charges or why some ions can have two different charges. I concluded it must be because of the number of electrons, but I am still unsure about why the electrons give off that specific charge for different elements.

At first, naming ionic compounds was confusing for me. I didn't know how to specify how many of each ion goes into the compound in its name. But then I learned that in naming these type of compounds, you don't have to specify how many ions there are because the charges always have to cancel out and then therefore the ratio may be inferred by the name. But what about ions the don't have a constant charge? I found myself asking. It wasn't until later in the week that we learned we specify the charge with Roman numerals ( i.e if we were using the single charge of copper, after writing copper we would write (I) in order to represent this). Then the second ion’s ending is either replaced with ‘ide’, if it is a binary compound, but if the second ion is polyatomic, then we use the name already given for it.

Because I struggled a lot naming ionic compounds, when we moved on to naming molecular compounds it came much more naturally to me. One thing I found surprising about the big difference between molecular and ionic compounds, is that always in the name of a molecular compound, the number of ions in each element is always specified. We specify this with prefixes such as mono, meaning one, di, meaning two, and tri meaning 3 and so on. Because I had worked with these prefixes in other classes, I was very familiar with them and they came very naturally to me when using them.

The biggest thing that I struggled with this unit was distinguishing between an ionic compound and a molecular compound. It wasn't until the weekend before the test that I realized that ionic compounds always contain metals that form one ion, and molecular compounds only contain non-metals. After I realized this things got a lot clearer and I did much better on the test. Although we haven't gotten into it that much, I'm still curious to know why some ions don't have charges that cancel, and ultimately what even causes an ion to have a charge.