Tuesday, October 19

Converting to Atoms, Moles, and other measurements
After going over last nights blog and talking to us about national mole week, Mr. Henderson began to focus in on the big idea for the day. Just as we have been doing for the past week or so, we started off by converting one unit to another. However, today we started with slightly more difficult conversion problems. Of course, I'm talking about converting moles to atoms, atoms to moles, atoms to grams, grams to moles and so on. Before I begin to go over pages 6 and 7 (the pages we worked on today), it is important to have a basic understand for some of the quantities we will be addressing.

First off, the one you will be hearing most about in this blog is the mole. 1 mole is 6.022x10^23 of something. This number was created to help us convert one atom to a useful unit, like the gram. This leads into my next point, the mass of atoms. On our periodic table, the mass of an element is known as XX amu's. This number can also be used to obtain the elements grams per mole. How you do this is actually very very very very simple. Take the atomic mass of the element and drop it into the g/mol unit! So, for example, oxygen's atomic mass is about 16 amu's. Therefore, oxygen is also 16g/mol. This is used so that we can speak of the units of each element in more relative terms, such as grams or grams per mole.

Now lets begin going over the packet pages starting with pg.6. The top of page 6 asks how many donuts or in 2 dozen donuts. This question is there to help us understand that a mole is nothing more than a way to help us speak more easily about atoms, like a baker uses the dozen to talk about the number of donuts he is baking. The next question asks how many atoms are in 2 moles of water. Since we know that 1 mole of atoms is 6.022x10^23, we automatically know that 2 moles of water would be 12.044^23 atoms, or 2 x 1 mole of atoms. Questions 4-6 are very similar and are used to help us understand just how large a mole is. The first question asks how much mass would 1 mole of .62kg basketballs have? So, as we would start of all conversions, we begin with the unit we are given which is 1 mole of basketballs, in this case. Now, our next step would be to put 6.022x10^23 basketballs / 1 mole of basketballs. Our final calculation would be to multiply the mass of a basketball / 1 basketball. We are now left with (6.022x10^23)x.62 kg. After doing these calculations, we get the answer......... 3.7kg x 10^23! If you still don't understand just how massive this is, the mass of the of the moon is also given. It is only 7.4x10^22. 1 mole of basketballs is 5 times as massive as the very moon that orbits our Earth!

(Yup, that moon)

Next, on Questions 7-9, we began to use the mole for what it is truly meant for; Converting atoms to more useful units of measurement. Our first question is How many atoms of lead(Pb) are in 5.0x10^-4 grams of lead? Now lets begin our conversion with 5.0x10^-4 g of Pb. Because we are looking to obtain a number of atoms as our answer, we will start with the next corresponding conversion factor, the mole. 1mole/207.2 g of Pb should be your next step because this is the number of grams that would result from 1 mole of lead atoms. Also, as we discussed earlier, it is the same amount as the atomic mass of lead on the periodic table. Finally, we will multiply 6.022x10^23 atoms/ 1 mole to cancel out our moles and get an answer. Although 0.0005 grams of lead may seem like a small amount relative to our everyday lives, It is still 1.45 x 10^18 atoms of lead! A massive number of atoms for a minuscule amount of grams.


The answer for pages 6 are as follows:

#1)24 donuts
#2)12.044x10^23 molecules
#3)10 (every power added to 10 multiplies the given amount by 10, in this case, moles)
#4)3.7 x 10^23kg
#5)3.8 x 10^ 14 years
#6)3.6 x 10^26 cubic centimeters
#7)1,45 x 10^18 atoms
#8)9.0 x 10^18 atoms
#9) 2.1 x 10^-22 grams (that's 0.000000000000000000000021 grams!)

As for pg 7, we just began to discuss the molar mass of compounds and the way to do this is probably the way you would have guessed. Just add together the mass of each elements in the compound. To obtain the molar mass of Barium Chloride (BaCl2), add the mass of 1 mole of barium atoms(137.33 g/mol) to the mass of 2 moles of chloride atoms (2 x 35.34 g/mol). Your answer should add up to 208.23 g/mol. We will continue on to finish this sheet tomorrow but all the answers we have gotten in class so far are as follows.

#1) 32 g/mol
#2) 58.45 g/mol
#2.5) H20= 18 g/mol (IMPORTANT FOR LAB MR1.)
#4) 208.23 g/mol

With the final 10 minutes of class, Mr. Henderson let us get back to our lab groups and finish up the lab with the knowledge that we had gained from question #2.5 on pg.7. Now we know that water is about 18 g/mol. Next, each group would have to find the amount of moles that was assigned to your group. This could be done by dividing the amount of molecules assigned to each group and dividing it by 6.022x 10^23 Luckily, all our group were assigned a number of molecules that could easily be divided by a mole. Finally, all that had to be done to solve this seemingly impossible conversion was to multiply the number of moles your group had by the grams per mole (g/mol) of water, which we know is 18 g/mol. Now you would be left with xx grams of water, and since we know water's density is 1 gram per milliliter, the last step was to change grams into mL and present your findings to Mr.Henderson.

I hope this blog helped clear up any confusion about molar mass and atomic conversions. Today was definitely a jam packed day. Good Luck!