Vocabularies and the Crystal Lab

The last couple weeks we talked about a lot of vocabularies.
One of those vocabularies is called soluble. Soluble is described as a substance that dissolves in a solvent.. That basically means if you already have a solvent like water, H2O, which already is a solvent and you add salt, NaCl, it dissolves in the water.
Another vocabulary is insoluble. Insoluble is the opposite of soluble. It is described as a substance that doesn't dissolve in a solvent. For example if you take a rock and water and you put the rock in the water it does not dissolve.
The next word we learned is miscible. This word means that two liquids are soluble in each other. Let's say we have ethanol alcohol, C2 H5 O, and water, H2O. The alcohol and the water mix so that it becomes one solution. In the end reacts to CH3 CH2 OH. After the reaction you have only a single liquid.
The opposite of miscible is immiscible. It basically means that two liquids cannot be mixed with each other. An example is water and oil. If you try to mix water with oil it won't work because oil is non-polar and oil is polar. And if something is non-polar it won't mix with something that is polar.

Then we have a word called solubility. Solubility is the maximum amount of solute that will dissolve in a given amount of solvent at a specific temperature and pressure.
We did a lab on solubility. We created crystals. We used a beaker and put some distilled water in it. Then we added alum. We stirred it until it dissolved. After that we kept adding more and more. When it stopped dissolving we put it on a hot plate to change the temperature. The temperature changes causes a greater solubility. Then we kept adding more alum. And again when it stopped dissolving we didn't add more alum because we couldn't hat it up more.
After it cooled down a little bit we put a pencil on top of the beaker and wrapped a little string around it. Then we let it stand overnight. The next day we walked in we looked at the crystals. They grew a lot.
This are two crystal we made.

The next word is saturated solution. A saturated solution contains the maximum amount of dissolved solute for a given amount of solvent at a specific temperature and pressure. If we wouldn't have heated the beaker with the alum in it we would have had a saturated solution.
There is another word called unsaturated solution. It is basically the opposite of a saturated solution. It contains less dissolved solute for a given temperature and pressure than a saturated solution.
If we would have put alum in the beaker and stirred it but not added more until it's saturated we would have gotten a unsaturated solution.
The last vocabulary is supersaturated solution. It is a solution that contains more dissolved solute than a saturated solution at the same temperature. This is what we did in our crystal lab. Since we heated the solution we could add more alum and therefore we made a supersaturated solution.
I think that we did a good job on the crystal lab because we got what we wanted, crystals. We got smaller ones and bigger ones. Smaller ones because we didn't completely get a supersaturated solution and big crystals we got a very good supersaturated solution. 

Evaporation and Intermolecular Attractions

This week we did a lab about several liquids  and their changes in temperature which were caused by  evaporation. The liquids we used were methanol, ethanol, 1-propanol, 1-butanol, n-pentane, and n-hexane. 

First of all we took two little pieces filter paper and and put it around the tops of two temperature probes. Then we put two rubbers around it so that it keeps holding it tightly.After this we connected the temperature probes with the computer. Then we put some methanol in one test tube and some ethanol in the other test tube. After this we put one temperature probe in each test tube. We waited about a minute and then we pulled the probes out and we put both probes on the table. We waited about 3to 5 minutes in order to see the highest temperature and the lowest temperature on the computer.
We did this procedure with for methanol, ethanol, 1-propanol, 1-butanol, n-pentane, and n-hexane.

Then we subtracted the lowest temperature from the highest. If you do this you figure out the difference between the highest and the lowest temperature. You can see it on the graph below. 

 

On the graph above you can see that both n-pentane and n-hexane have the highest difference between the highest temperature and the lowest temperature. 

This happens because of the hydrogen bonds. Since n-pentane and n-hexane are not alcohols they don't have an   O-H group so the H cannot form a bound to the other n-pentane/n-hexane. 

In contrast alcohols do have an  O-H group. The hydrogen atoms are charged delta positive because it gives his one electron to the O and then it's out of electrons. And if an atom gives away an electron it is charged positive because electrons are charged negative so the atom loses its negative charge. But because the O gets an electron from the H it's charged delta negative because it gets an electron which is charged negative. So the Delta positive charged H(of one alcohol) and the delta negative charged O(of another atom) attract each other enough so that they kind of form a bonding even without electrons on each sides.Then there is a surface tension. This leads to that the alcohols are harder to pull apart because they are connected even though they are no connected with electrons. So now the atoms they are more sticky because of the O-H bond. The O-H bond avoids that little molecules can come out of the alcohol so its temperature difference is not as high as the temperature difference of the not alcohols.
As you can see on the chart above 1-butanol has the lowest difference in its temperature. This happens because it has very many O-H bonds so there are even less molecules released during the reaction. If we kept going and we used for instance pentanol (the alcohol) the temperature difference would be even less because it has more O-H bonds than 1-butanol. 

Since n-pentane and n-hexane are not alcohols they don't have the O-H bond and they do not have a surface tension which makes them lose more molecules than the alcohols do and they are not very sticky, either.

Silver/Copper Replacement Lab

The lab we did was about a silver/copper replacement and about if we know the mole ratios so that we can give an educated guess or a prediction about how much silver/copper we are going to have after the lab.
At the beginning we cut some copper (about 30cm). Then we cleaned it with a plastic sanding pad. We cleaned it so that there is nothing else on it, like dirt. After we've done it we twisted the copper around a pencil so that it looks like a "spring".

After we did that we weighed the copper coil. Its weight was 2.201 grams.
Then we took some silver nitrate and weighed it. Its weight was 1.022 grams.  Then we put the silver nitrate in the test tube and covered it with a piece of parafilm so that no liquid could get out of the test tube because we also filled the test tube with distilled water.
 Then we shook the test tube so that the silver nitrate and the water balance each other.
After it we removed the parafilm to add the copper wire. Then we put the parafilm on it, again. Then we observed the reaction. The copper wire and the silver nitrate began to react and the copper wire looked kind of green-ish blue-ish. The test tube was also a little bit hot so heat has been released.
We let it stand overnight so it could react completely.
The next day we kept going on with the lab.
At first we took a little filter paper and weighed it. It weighed 1.421 grams.
Then we shook the test tube to get the silver off of the copper wire which is in the test tube. After we're done with this we put a filter paper in a waste beaker so that we could collect all the silver.

Then we opened the test tube and took the copper wire and put it aside. We took the test tube which contained silver and put all this in the filter paper so that we could get rid of the liquid that was in the test tube (mostly distilled water). Then we put some distilled water on the silver in order to clean it completely from everything that could have been on it. After that we put the filter paper with the silver on it somewhere to let it dry overnight because when it has water on it it weighs more than the silver does when it's dry.  The next day we weighed the silver and the copper wire. The silver on the filter paper weighed 2.075 grams. The copper wire weighed 2.015 grams.
Then we compared the mass after the reaction and before the reaction. We got 0.644 grams of silver and lost 0.186 grams of copper during the reaction and the lab.

After we had weighed the Silver nitrate in the beginning of the lab we made a prediction about how much silver we will get after the reaction.

To make the prediction you have to: take your amount of silver nitrate in grams(1.022)* 1mol of AgNO3 (silver nitrate) * 2 mol of silver * 1mol of silver in grams (107,869 grams) and divide all this by 1mol in grams of silver nitrate (169,87 grams) * 2mol AgNO3 8 1 mol of silver. 
You get the numbers in the middle ( 2mol of silver and 2 mol of Silver nitrate) by looking at the equation of the chemical reaction which is    2AgNO3 + Cu  reacts to    Cu(NO3)2 + 2 Ag.
If you do so you get a prediction of how many grams of Ag you will Get. Our prediction was that we will get 0.649 grams Ag.
To determine the prediction for copper you do the same procedure but with the numbers of copper instead of Silver Nitrate. The prediction for copper was 0.191 grams.

But after weighing the silver after the reaction we only got 0,644 grams. To determine how many percent you're off you  divide the number you got by the number you predicted. Our result matched to 99.23 percent with the prediction so we were only 0.77 percent off.
After weighing the copper we got 0.186 grams. This result matched to 97.38 percent with the prediction. We were 2.26 percent off.
I think that we did a pretty good job because the most we were off was about 2 percent which is very few.

The Mole

We have talked about the mole for about 2 weeks so far. First we talked about what a mole actually is.
A mole is pretty much a huge number. It is 6.02x10^23. It was invented by Amadeo Avogardo. The number is always the same because a mole is a mole so the number never changes if you work with moles. Since the number is always the same the mass can differ. The molar mass is also shown on the periodic table. It is shown in grams. There are weird numbers above the atom like 15.9994 (O). This tells you how many grams of the particular atom equal one mole. There are also 2 conversion factors: 6.02x10^23 divided by 1mole         and        1 mole divided by 6.02x10^23. With these conversion factors you can see how many grams you need.
After we've figured out all that we've talked about how you covert from grams to mole and from mole to grams. It took us quite a while but then everybody figured it out.
If you know how many grams you have you need to divide the grams by the number of the atom that is shown on the periodic table. Then you know how many moles this amount has. If you know how many moles you have you have to multiply by the number of the atom that is said on the periodic table in order to find out how many grams this amount of mole is. If you have a compound of elements like NaF and you want to know how many grams there are in a certain amount of moles the first step you have to do is that you have to add both the number of Na and the number of F and then you can work the way I just described.
We also talked about how to find out how many percent of one atom there are in a compound. Let me give you an example. You have C5H8NO4 and you want to know how many percent of the compound is C. Then you take the mass of C5 and you divide it by the mass of the entire compound and then you multiply it by 100 in order to find out the percentage. In general you take the mass of the atom of which you want to find out the percentage (if there are like 5 of these atoms you take the number times 5) and then you divide it by the mass of the whole compound. That's the way to find out the percentage of an atom in a compound.
After that we did a little experiment about how to convert a recipe. We had the numbers of moles and grams and particles and we had to find out how much you need of everything. But for luck the conversion factors were said on the back of the paper so it wasn't too hard to figure it out.
Then there is something called empirical formula. the empirical formula shows you the ratio of how many atoms you need in a compound. There is also the molecular formula. This tells you, if you have figured out the ratio of atoms in a compound, how many of these atoms you need because you know the grams of the compound but it might differ from the actual mass of the compound. You can see that if you add the number of the compound you have and you subtract the number you got from the empirical number and then you know whether or not you need twice as much of this compound or only the half or more or less.
The last experiment we've done was a Popcorn experiment. Since I have already explained how to figure out how you can find out the percentage, we had to do it. We used a beaker, oil, cover, and kernels to make popcorn. First we put some oil in the baker and then we weighted it. Then added the kernels and weighted it again.  Then we put the cover on it. After this we put some holes in the cover. Then we heated the beaker with the kernels and the oil in it. After the kernels have pooped and turned into popcorn we waited until the beaker cooled down. Then we weighed the beaker with everything again.  Then we weighted it again too see how much water was lost. After the heating it lost 1.3 grams. This is how much water the kernels lost during the reaction. Then we took the difference between the grams of the beaker with oil and kernels and the cover and the beaker with the cover, but without kernels(3.3 grams). Then you divide the smaller mass (1.3grams) by the bigger mass (3.3grams) and divide it by 100 in orer to find out how many percent (like in this case) the popcorn lost(39%).