May 28-31

This week primarily focused on the Coke bottle lab. In this lab, I had to make the silver precipitate that would form on the inside surface of the bottles.

The first step I took was drinking the pop. This I did, and even though I wanted to rinse it out with water, I was told not to. This makes sense because the water would interfere with the chemical reaction and perhaps cause disassociation.

In every experiment, of course, following the instructions is important. That is why I ensured that I was double-checking the instructions. I made sure that I was using 10 mL of glucose, for example, not 50. The proportion of the reactants is very important in a reaction, and if there is too much of one reactant, then not enough of the excess reactant will react. It could ruin the experiment.

In the experiment, I measured out 10 mL of glucose and put it in the bottle.

I then got the silver nitrate and volumed it at 40 mL, but did not put it in with the glucose since the instructions said not to. I thought that since the silver nitrate would have to go in with the glucose eventually, what would happen if it were mixed with glucose first?

The next step I took in the experiment was I added drops of ammonia to the silver nitrate. As soon as I did this, a brown precipitate form, but to dissolve it, I added more ammonia. This I think happened because the silver nitrate was an aqueous solution, and the ammonia ions separated the silver nitrate, hence forming the precipitate. The more ammonia ions there were, logically, the precipitate would eventually dissolve depending on the number of ions it needs. This then formed silver ammonium (Ag(NH3)2).+

Then, I added the 15 mL of potassium hydroxide to the silver ammonium complex. Then, I combined this with the glucose inside the bottle. In order for the reaction to occur, though, I had to shake the bottle in order for the particles to collide together, hence the electrons could be transferred from one element to another. Hence, motion also plays a role in catalyzing chemical reactions.

The bottle, of course, needed to have a stopper so that none of the substance would come out. So, I sealed it carefully before I shook the bottle. As I continued shaking the bottle, I noticed that it was turning black. As the instructions said, fine particles of any metal are black. This was how it appeared when I performed the experiment, so I knew I was doing the experiment correctly. As soon as the coating appeared to be even, I stopped shaking, and now I'm waiting for the solution to solidify to form the silver layer inside.

This reaction, overall, is known as the Tollen's test, which is used to identify the aldehydes in the reaction. The mirror forms when metallic silver deposits on the inner surface of a glass container solidifies, hence forming the silver precipitate. In this experiment, the aldehyde was glucose. When it combined with the ammonia complex of silver in an aqueous solution, the silver was eventually disassociated from the rest of the complex, hence isolating the ions to form the silver precipitate.

This would explain how mirrors are made. In normal mirrors, the silver is used, and since the test forms reflective silver, light can reflect off of it due to its physical and chemical properties, which explains why mirrors often look silver, or depending on the color of the metal used like copper, the light reflecting off the mirror makes it appear to be that particular color.

This week, I also reviewed over the whole course of the semester. The concepts that I learned this semester played into this lab. One of the basic concepts that played a role in this lab were the properties of matter. In this lab, I observed that the silver nitrate, the potassium hydroxide, and the ammonia were all liquids. This was different than most of the chemical reactions because if look back on the copper chloride experiment, for example, a solid (copper) reacted with a liquid (chloride) in an aqueous solution in water. Water happened to separated the ions through disassociation. But, in this one, all were liquid, which may have played a role because they didn't require a solvent to form an aqueous solution. Rather, it required the glucose to react to help form the silver precipitate.