Sunday, May 15, 2011

Acids and Bases

To finish off chem class we have been working with acids and bases. We have done two labs now that deal with this concept. In one lab we had a variety of common acids and bases that we see around in our daily lives. These included things such as Pine Cleaner, Tums, orange juice, etc. We tested these common household items by putting a small amount in a baggy with some red cabbage juice. This juice turned the acids and bases colors so they were easy to identify. We used this indicator to tell us how acidic or basic.
The other lab that we preformed was a bit more complex. In this lab we started out with a beaker of acidic solution on a Bunsen burner with a constant stirring magnet inside of it. Above this acidic solution we have a temperature probe that hangs down just far enough into the water that it picks up accurate readings and there is also a buret hanging right above the acidic solution containing basic solution. First in this lab we put a few drops of phenolphalien in our acidic solution for a color change so we could see the process happening. We constantly released some of the base into the acid until our data showed a drastic change in data. This giant data change showed the number at which the acid changed to a base and it gave us the measurement for the unknown concentration of the acid.
                     This is what our data looked like:
These two labs both showed us the basics of acids and bases. To summarize all we have learned up really quickly its as simple as this:
1) pH scale: 1-14, 7 distilled water = neutral,  1-6 acid, 7 neutral, 8-14 base
2) water is considered neutral because its H+ and OH- are equal
3) when there is more H+ the solution will be an acid such as HCl
4) when there is more OH- the solution will be a base such as NaOH
5) red cabbage and phenolphthalein are examples of indicators that show evidence by different shades of color, whereas a temp probe is an actual measurement of hydrogen ions with real data evidence.
6) acids = red, pink      neutral = yellow, purple(if cabbage juice)       base = blue, green
7) moles/L = molarity or 1 X 10^-7 moles/L <-- neutral equation to find any pH take the exponent without the negative sign and that will give you your answer
8) acids and bases make up a lot of the common things we see around us such as food and cleaners. some can be dangerous, but for the most part if you use them correctly they are very good things to have around

Thursday, May 12, 2011

Chemistry Solutions [CH 15]

For my Chemistry Solutions post I decided to use and make flash cards to study the terms for everything that deals with solutions.
Here is the link

Monday, May 2, 2011

Gas Laws

Recently in Chemistry, we have been dealing with the types of gas laws and then we even went into how all of those laws work together to create an ideal gas law. This ideal gas law helps you to identify unknown gases or pieces of the equations when one variable is needed.

Let's start back with the lab we did earlier this week. This lab was known as Boyle's Law: Pressure-Volume Relationship in Gases. This lab was based around the law K= P1 X V1 meaning that K (constant) is equal when the pressure and volume are multiplied together. This can also be written as P1 X V1 = P2 X V2 meaning that data has been collected about pressure and volume at one time should have about the same constant as data collected about pressure and volume recorded at a different time, therefore we set them equal to each other. When we preformed this lab, it was very simple, we used a
Volume and Pressure Connection
syringe and a gas pressure sensor connected to the computer to collect data that shows the connection between volume and pressure. We were trying to decide if pressure and volume were direct or inverse. The direct formula was P/V and the inverse formula was P X V and since that was our equation we knew these two conditions were inverse. The inverse conditions means that when volume decreases, pressure increases and when volume increases the pressure decreases.
If we analyse this data table from the first experiment we can tell that pressure and volume have an inverse direction. This graph clearly that as volume increases the pressure drops at a fairly rapid rate. From the 5.0ml to the 7.5ml the pressure drops about 44atm. From 7.5 to 10.0 and 10.0 to 12.5 the pressure drops about half of that amount. As the volume starts getting even larger we notice a less drastic pressure change, but it is still decreasing. This inverse relationship plays in with the ideal gas later explained later in my blog.
We did a few more labs after Boyle's Law, one of those including Pressure Temperature Relationship In Gases (Gay-Lassac's Law). In this lab our groups had a flask with just regular air in it. We had the flask sealed so that our pressure was always in a constant volume. Then, we took our flask around to different stations and placed our flask and temperature prob into bodies of water with different temperatures. We measured the temperature of 4 different tubs of water and our pressure for each we recorded as well. Our data read as follows:

From this data chart we can clearly see that as temperature increases pressure increases. Because both of these factors rise together we can infer that they have a direct connection between them when volume is constant. Finally, since these two are direct, their equation is know as K=P1/T1, which means that any point on the graph can be pressure divided by temperature and it should have the same konstant as another point on the chart. Because this is the case, just like Boyle's Law it means that P1/T1 = P2/T2. Again, this means that one pressure and temperature should be constant to another pressure and temperature calculation at another time and their constant will still be the same.

Finally, the third law is the law created by Charles. This law states that volume and temperature have a direct connection between them as well. So, if temperature increases, volume increases; if temperature decreases, volume decreases.  The equation is V1/T1 = K or V1/T1 = V2/T2. We did not do an experiment for this law, but we talked about it and because the connection is direct like the pressure and temp law, if data were collected the graph would look similar to the chart for that experiment of Gay-Lassc's law. Although we didn't do an experiment an easy example is of a helium balloon in a car. If the temperature is hot, the balloon has a good chance of popping because it's volume increases bigger than the balloon's barriers can hold. If it is a cold day, the balloon may shrivel up and sag.

As you can see from all of these experiments, these 3 factors play a large roll all together. Therefore, these factors, when placfed together make up the Ideal Gas Law. This law is written PV = mRT (pressure X volume = mass X constant R X temperature). This law can be used to find missing variables of an equation or identify the gas of an unknown substance. In order to do this we need to move the equation around to read M = mRT/PV. M stands for molar mass (g/mole). To find M, we must measure and plug in all of the other varibles. The varible m, is the mass (grams) of the substance. That is a good one to start with. Next, replace R with the number .0821 which is a constant. Then, measure your temp [degrees K (degrees C + 273)] and place it in the equation. Pressure is pretty constant at room temperature, but it can vary depending on altitude and humidity; here is La Junta, CO pressure at room temp is about .8 atm. Finally, calculate your volume and make sure it is in L not mL. When all of this is complete and the equation is calculated you will get what the gas's molar mass equals. This is a fun and easy way to identify and understand gases and their laws.

-working on data analysis and self analysis

Friday, February 25, 2011

Intermolecular Lab Review

        In this blog I'll be giving my review from the Intermolecular Lab that my chemistry class has been preforming these past few days. The first day we did a simple Pre-Lab. In this preparation lab we were given a list of all of the substances that we would be working with and their formula. With this information we created a structural formula for each one. We also found each of these substances molecular weight (graphs x-axis) and whether or not it had a hydrogen bond or not. The next day when we came to class, we did the first part of the lab which dealt with ethanol and methanol. For each, we had a test tube of the substance (compared 2 at a time) and a probe wrapped with filter paper at the tip held on by rubber bands (separate for each substance). We repeated the process (for the other substances) of dipping the probes into each substance for 15 seconds and then pulling them out simultaneously as we watched the computers, which the probes were hooked to, to see which substance temperature would decrease the most (graphs y-axis). Our data chart read this informations:

SUBSTANCE:               INTIAL TEMP:           LOWEST TEMP:        CHANGE IN TEMP:
ethanol                                 21.3 C                                8.4 C                           13.4 C
methanol                              23.7 C                                1.7 C                           22.0 C
propanol                              21.8 C                               14.5 C                             7.3 C
butanol                                22.7 C                               18.1 C                              3.6 C
pentane                                21.9 C                                 -.9 C                            21.0 C
hexane                                 21.4 C                                4.2 C                            17.7 C

Between each of these testings we made predictions of each substances temperature change. We were never right on, but several of them came pretty close. We based our predictions off the previous experiment testings of ethanol and methanol. We figured that the bigger the mass the less the temperature changes, which was correct, but as I said, none of our numbers were right on.
     Finally, after we had collected all of our data, we did a Post-Lab where we processed our results. We used our data from the pre-lab and from our data table (shown above) to make a graph of the substances to show how molecular weight affects the change in temperature. As we had predicted, the larger the mass of the substance the less it changed in temperature and that was proven by this graph of our data (pentane and hexane not included in this explanation).

        To explain this graph and this whole lab a bit more and wrap up, I would like to tie all of this together back with the term intermolecular forces. As I stated before, we concluded that the larger the mass a molecule has the less the molecule changed in temperature and this is because of intermolecular forces. Here you can picture something really sticky vs. something easy to break, a rice crispy vs. a dry cookie. This relates to intermolecular forces because the larger the substance, the more complex it is, meaning the more atoms it has to hold it together, therefore being a lot like the rice crispy and more resistant to fall apart. A substance more like methanol however, tends to be a lot more like the dry cookie. Methanol's structural formula contains one carbon and a few hydrogens hanging on and connected to an oxygen and a hydrogen. This is a fine structural formula, but it isn't sticky. The bonds between these substances aren't as strong causing the substance to be much easier to just break apart, resulting in evaporation taking some of the heat energy with it and larger temperature changes. As for how intermolecular forces deal with temperature change it's like this: if a molecule is larger and "stickier" then during the reaction more energy is used trying to break down the substance rather than changing its temperature and if a molecule is smaller and "less sticky" then it doesn't take the reaction long at all the break down the substance so it has more energy to work on changing the temperature.
        Overall, I liked this lab. I thought it was a fun hands on way to understand how molecular weight can change the temperature. I understand the concept that a molecular weight affects the change in temperature of a substance. For example, the lighter the substance the more its temperature will change and the heavier a substance the more likely it is for its temperature to be fairly close to its original. From this blog I would really like to achieve a 4 in communication and lab skills, because I feel I understood this well enough to share it in an easy-to-understand blog and my lab skills were EXCELENTE! :)

Monday, February 7, 2011

Silver Copper Replacement Lab

Copper Coil
     Copper wire reacts with aqueous silver nitrate. The relative amounts of the reactant and product are determined from the mass loss of copper wire, the starting mass of silver nitrate, and the mass of silver metal obtained. In the experiment, copper changed from its elemental form, Cu, to its blue aqueous ion form, Cu2+(aq). At the same time, silver ions (Ag+(aq)) were removed from solution and deposited on the wire in the elemental Ag metallic form.

     This lab took our class about 3 days to complete. Day number one, we got our materials ready and weighed out. We then took the silver nitrate (AgNO3) and mixed in distilled water until the AgNO3 had dissolved. After that, we placed the copper coil in the test tube as well and let it set until day two. Finally, we went back to class and used math with the balanced equation 2AgNO3 + Cu ----> Cu(NO3)2 + 2Ag and we formed predictions for how much silver should be formed and how much copper became Cu(NO3)2 in the reaction. Day number two rolled around and we observed a sort of crystal looking structure that had formed around the copper wire. We gently shook the test tube to dislodge this formation like the instructions requested. Then we set up a funnel with filter paper with a waste beaker underneath and we lifted the wire from the solution and dumped the remaining solution & silver mixture into the filter paper. Once it had drained we set both the wire & filter paper with the silver under the fume hood to dry. Day three and this was just to finish up the lab. We weighed the copper coil and recorded it's mass and did the same with the silver and filter paper. Now we had all the measurements needed to make out figures of how much Ag was formed & how much Cu was lost.

We used alot of moles in this lab.
There was lots of converting
grams to moles and back again.
     Our predictions said that we should expect to form about .7703g of Ag and loose about .2269g of Cu. With our measurements we did some more math to see if this prediction was correct. First was changed the number of moles of silver produced to moles and got .0103 mol. we did the same for number of copper consumed and that was recorded at .0036 mol. When divided by the smaller mole we got a 1 to 3 ratio of Cu to Ag. This information was compared to our predictions which had stated we would have a 1 to 2 ratio of Cu to Ag. When compared, we got 144 percent yield meaning that we got a considerable amount more silver than we had expected, but for the amount of copper used, we got 100 percent yield so we were right on target there. Overall, this lab, the Silver/Copper Replacement Lab, was a fun way for our class to learn more about mole ratios in a hands-on way.