English Component
Narrative Essay
In all of my science classes, I have learned so many basic things. It has always been the bare minimum, with no extra details, or no explanation of why does this happen. One of the few things whose why has always evaded me has been solubility, or what solutions will dissolve into others. I had always just been told that it happened, and I had never known why, and it had always irritated me. Until we received this project, where we were able to investigate something that we were interested, which is why I decided to do an experiment using what I had learned in Chemistry to see how polar and nonpolar covalent and ionic substances dissolve in each other.
The first thing I had to do for this project was to learn more than the basic information about covalent and ionic bonds. Covalent bonds occur between two non-metals, with some having specific charges on the side of the molecule and others without. That is the difference between the polar and nonpolar molecules; the polar ones have the charge and the nonpolar ones don’t. Ionic bonds on the other hand, are between a metal and a nonmetal, and don’t have any classifications like polar or nonpolar. After I learned what those terms meant, I actually had to find substances that fit those classifications. I decided that I would have two liquids, one polar covalent and one nonpolar covalent, and an ionic, polar, and nonpolar solid to add into them. In the end, I ended up using water and olive oil for the polar and nonpolar liquids respectively, and sugar for the polar substance, melted paraffin for the nonpolar substance, and salt for the ionic substance. I measured out 50 mL of the two liquids, and weighed them. After that, I kept adding in the covalent solids 1 gram at a time, one at a time, into both liquids, and then stirred and shook them until there was a leftover solid in the bottom of the test tube. After that, I decanted and removed all of the liquid using the pipet, and weighed the leftover solids. I also did this at very cold and hot temperatures, to see how it changed.
When I first began my experiment, my hypothesis was that the solids would dissolve in the similar solutions, while the ionic substance would dissolve in both liquids. However, I was somewhat incorrect. The ionic substance, the salt, only dissolved in the water, or the polar liquid. But I was correct in saying that the polar and nonpolar solids would only dissolve in their respective liquids. The paraffin, or the nonpolar substance I used, kept solidifying too quickly, but from what I could observe, it dissolved a little bit in the nonpolar olive oil, while it just formed over the water, not dissolving at all. With the temperature, the hotter the liquid was, the more substance that dissolved, and when the liquid was cold, barely anything dissolved, even when they did normally. There were many ways to measure the exact amount of how much dissolved, but I measured it by using a solubility constant and finding the difference of how much was left. For a more detailed explanation on how I found my information, and how you measured solubility, I also interviewed Dr. Hans Weger, whose PhD is in nuclear engineering and whose doctoral dissertation was the solubility and speciation of plutonium(VI) with phosphate. In order not to make this paper not exceedingly long, that interview and more detailed information can be found below.
Solubility is not a new concept. It is used in everyday life, whether we are aware of it or not, such as in making chocolate milk from powder or using soap to make to oil on your hands soluble with water to wash them. There is no major impact of this project, as everything I learned in this project has already been proven and implemented into people’s lives. However, this project did give some understanding into a topic that I knew nothing about, and if people knew what I learned, they could know why things dissolve the way they do, and possibly enhance their everyday life by improving any procedure where dissolving something is necessary.
Interview with Dr. Hans Weger
What exactly is solubility?
Solubility is the maximum mass of a solid that will dissolve in liquid. For example, the solubility of sodium chloride is (NaCl) 359 grams per liter (g/L). If you add 360 grams (g) of NaCl to one liter (L) of water, only 359 g of it will dissolve. The remaining 1 g of NaCl will form a wet solid residue on the bottom of the flask. Any additional NaCl you add to this flask will not dissolve.
From the results of my experiment, I know that polar and non-polar substances do not dissolve in each other. Why exactly does that happen?
The atoms in a polar molecule are arranged in a manner that one side of the molecule has a net positive charge and the other side has a net negative charge. The electrons are shared in a way that the -1 charge and the +1 charge do not fully cancel each other out. For example, water has a slight negative charge at the oxygen atom and a slight positive charge at the two hydrogen atoms. The negative side of a polar atom is attracted to the positive side of another polar atom, thus increasing its solubility. If the solid is not attracted to the dissolving liquid, it will not dissolve.
Non-polar molecules do not have a slight or partial negative and positive charge, so the polar molecules do not dissolve into non-polar solutions. However, non-polar substances will dissolve in non-polar liquids because they are similar in structure.
I didn’t have a chance to test a metallic bond in this experiment. What would have been the results of a substance with a metallic bond trying to dissolve in a covalent or ionic substance and vice versa?
Metal is very insoluble in most solutions. Metal workers have to heat the metal to very high temperatures to its melting point in order to be able to work with metal or alloy two metals together. You can leave a nickel, dime, or a penny in water or acetone for years and it will not dissolve at all.
Is how I did my project similar to how real labs measure solubility?
You only approached solubility from one direction: under saturation. A real lab would approach solubility from under saturation (add too little, then add more, then add more until the solid stops dissolving) and over saturation (put in too much and measure how much does not dissolve).
Also, the kinetics of solubility is slow. A real lab would wait weeks for the experiment to finish. In an over saturation experiment, a sample of solution would be removed and measured every one or two weeks until the dissolved concentration stopped changing. Also, sometimes the solubility will change abruptly after several weeks because the solid will change from amorphous to a crystalline phase or to a different crystalline phase, which changes the solubility.
What are the different ways to measure solubility?
See my answer above concerning under and over saturation approaches to measuring solubility.
In my project I define K as a solubility constant and as grams solute divided by grams solvent. What exactly is the solubility constant and are there any other units and measurements for solubility?
Solubility can be defined as either a solubility constant or as grams solute per grams solvent or volume of solvent. The value of grams per liter can be derived from the solubility constant and could be considered as a different way of expressing it. A solubility constant is typically defined as the ratio of the moles of dissolved product divided over the moles of the solid. The chemical reaction for solubility is [AB] (s) = [A](aq) + [B](aq), where AB is the solid and A and B are the two products formed when the solid dissolves, the brackets indicate that the units are chemical activity, (s) means solid phase, and (aq) means aqueous phase. The activity of a solid in solution is one. Solubility constants allow chemist to easily determine the effect of other solutes in a solution. For example, if you are dissolving NaCl into a solution containing Na from dissolved NaHCO3 (lets say 0.1), you can determine how much NaCl will dissolve by solving K = ([Na]+0.1)*[Cl].
How is this concept relevant in the world, and how can it improve it?
Solubility is needed to know how chemicals will react in processes for making things such as plastic, chocolate mike (solubility of powder in milk), or bleach. Solubility of medicine in stomach acid and in blood is vital information to know if or how the medicine will work. Solubility is needed to know make sure drinking water is clean. or to clean up a pollution spill.