This week we learned about moles. Did you know that the mole is 6.02 X 10^23? Well we learned how to concert moles in factor label. We also got assigned a fun little blog about moles! To prepare further for this class I will not let my frustration get in the way of my learning capabilities. Next week I will try to manage my time widely and not let my frustration intimidate me.
Recently in chemistry we have been learning about the infamous mole. Despite the fact that we learned about the burrowing creature in biology, the chemistry mole is just a gigantic number. Avogadro’s, not avocado, number is simply 6.022 X 10^23. This seems pretty intimidating at first, but as you work with the mole one can realize that it is just another unit of measurement like dozen or ream. The mole is just the chemists way of keeping the “flow” going simply. It expresses the amount in a chemical substance. It tells you how much of an element is in a certain substance.
This explore lab was quite the doozy. First, we matched 50 beans from 5 different types! After we massed them we found their relative mass and then ranked them from lowest to highest, in mass that is. We then counted exactly how many beans fit into the relative mass by adding them one-by-one to the balance beam until we reached the relative mass. This created the “pot”. Little to our knowledge the “pot” too had a double meaning! The pot represents the famous MOLE! No this is not the dirt burrowing creature, the mole is simply just another unit of measurement that makes chemistry that much easier. You can see the moles relation to the pot because the pot is measuring how many beans make up the relative mass of a certain type of element. Moles do this too. Moles use the relative mass of each element to find the amount of any element substance. The relative mass was used to find the number of beans in the pot. But why? Well, you divide the mass of the 5 different types of 50 beans by the smallest bean mass you have, which in this case was the lentil at 2.532g. This gives you the relative mass! You use this mass to determine the number of beans in the pot because the relative mass is approximately the mass of the pot. So you then add your beans and you can determine how many beans are in each pot. A pot is a model for the mole because the mole, like the pot, also hold multiple atoms, or beans, according to the relative (or atomic) mass. The average atomic mass is used for the mole because scientists have found using the average weight for the atom instead of the different isotopic versions worked out better. Why? Because it is the average! Sometimes it will be higher is some atoms and sometimes it will be lower, but don’t fret! Overall the atomic mass is the better choice because it gives scientists, like you and me, a closer look at the atom itself.
Alright so say you are a renowned chemist, but you have a flaw: you cannot figure out the percent composition of a certain compound! Before your hair falls out due to the agonizing stress, take a deep breath and we will go through percent composition step-by-step. Ask yourself: What exactly is percent composition? Percent composition is the percentage by mass of each element in a compound. Why does this matter when dealing with chemistry? Percent composition is important because it shows how much a certain substance is comprised of one component or other. How do I figure this glorious aspect of chemistry out? Well lets go through a few steps.
Say I have H2O. What percent of this compound is Oxygen?
First, you find the molar mass of each of the atoms. Hydrogen is 1.01g and there’s 2 of them so that is 2.02 g. Oxygen’s mass is 16.00g grams. The total mass is 18.02 g.
*you can find the atomic masses on the periodic table. Just look for the atomic mass and plug it in!
When you think of percent composition try to always remember Part/Whole. Put the part you are trying to figure out on the top and the total mass. For our H2O example, since we are trying to find oxygen, put 16.00g/18.02g. That was the mass of the oxygen versus the total mass of the compound. Divide these and you should get .887 remember your significant digits like we talked about in the other blog! Try to keep them consistent.
Lastly, you are going to multiply the decimal you calculated by 100, which will give the percent. In this case oxygen is 88.7% of the compound H2O.
Why is this important? Well, one can use percent composition to figure out chemical formulas and determine the different amounts of elements in compounds which would be very useful in a trial and error experiment.
If you need extra help with percent composition, or you want to review more examples visit the site listed below.
To be precise or to be accurate now that is the question at hand. What do these two things mean? Lets give a little background first. Significant digits, or sig digs as I like to call them, are numbers that contribute to the precision of a whole number. The Atlantic-Pacific rule, contrary to what you may believe, is not about our major oceans at all! What this rule states is that if the number has a decimal, you count from the left, or pacific side at the first nonzero number. For example .0010 would have 2 sig digs because you count starting from the one! If there is no decimal place you count from the right (Atlantic) side starting again with the first nonzero number. For example 10 would have one sig dig because the zero doesn’t count! Again, Significant digits all contribute to the precision of a number. What is precision? To be precise is to carry the measurement you are taking to the last possible number. If you have a 3 beam balance that means you have 3 precise measurements, but you always estimate a fourth because its science and science likes to be precise! To be accurate is to have a count of something. If you have 10 m&m’s you do not need to measure this you can simply count it, and that is what accuracy is about. So what? What is the big deal with all these numbers? It doesnt matter! Of course it does! Significant digits is a way of telling how precise your data is. If you have 8 grams of sugar and 8.2 grams of sugar, sure that is not much of a difference. BUT IF you have 1.44 million dollars and you round it to 1 million you are losing 440,000 dollars just because you were not precise enough to put your significant digits. What a waste!!
Hydrate composition say what? Yes it is true, you can find out what percentage of a certain Hydrate is water. How do you do this miraculous deed? First you mass EVERYTHING. Mass the evap dish, and evap dish with compound hydrate. Then simply heat the evap dish with the substance on a ring stand over a bunsen burner. You then shall wait until the evap dish is cool, then mass that as well. Your mass should be lower than the first mass because you are evaporating water from you substance! To make sure you evaporated all the water out. Heat the evap dish again for 3-5 minutes! Then what do you do? MASS AGAIN. Your two masses after heating should only vary .02 if it differs any more than that you will have the pleasure to heat and mass again. Thankfully mine only differed .01 grams. Once you have all your data, you can put the mass of the water (which you can calculate by finding the mass of the hydrate which in my case was 2.08 g and the subtracting that from the second mass after the heating, which was 79.41 g) which is 1.32 g and divide this by the mass of the hydrate, 2.08 g. You should get .365 then multiply this by 100 and you have your answer 36%! Now does this mean the results are completely reliable? No! The stirring rod we used had some substance on it when taken out which could have effected the mass of the substances. If you used 6.0 g of hydrate you would still lose 36% due to our calculations which would approximate to about 2.16 g of water loss during the heating. The results could change if the hydrates spatted out because that effects the overall mass which would mess up the calculations. For example if approximately .05 grams spatted out, this means not all the hydrate may have evaporated which would largely affect the overall data collected.
mass wtr/mass hydrate X 100 = percent comp of hydrate
90.00 g H2O/249.60 g CuSO4 = 36.05% H2O
CuSO4 * 5H2O Total mass of hydrate is 249.6 g because Copper is 63.50 g, Sulfur is 32.07g, O4 is 64.00g, H2O is 18.00 and you have 5, which means there’s 90.00 g H2O.
actual-theoretical/theoretical 0 .76-0.75/0.75 = 0.01 Percent error
This week my main task was to get through most of my nomenclature, which I did successfully! YAY! We also switched chapters this week into measurements and such. We learned of Significant digits. We also reviewed factor label which was challenging for me because I am terrible at it. We took a quiz today, Friday, and I am pretty sure I need to work on about everything that was on that quiz because I personally don’t think I did reasonable. I plan on getting help on this section a lot actually. I also plan on turning in everything in on time which is a big improvement for me. Yay for being proactive!