### Fundamental E3

Posted:

**Sat Oct 06, 2018 10:58 am**Please help I don't understand this problem! See attached IMG

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=8&t=33185

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Posted: **Sat Oct 06, 2018 10:58 am**

Please help I don't understand this problem! See attached IMG

Posted: **Sat Oct 06, 2018 11:42 am**

3 more Astatine atoms would be needed to balance the 9 Gallium atoms on the scale because Astatine's molar mass is 3 times more than a Gallium atom.

Posted: **Sat Oct 06, 2018 3:33 pm**

Dived the number of atoms on each side (meaning 9) by the two respective molar masses and look at the individual weight of each atom for each side. That should help you understand it better on how to balance out each side.

Posted: **Sat Oct 06, 2018 5:24 pm**

So you know the left side is fixed with 9 atoms of gallium and you want the scale to be balanced. So find the mass of 9 gallium atoms by multiplying 9 by the molar mass (70 g/mol) which gives you 630 grams. Then to balance the other side you need to have 630 grams of astatine. So multiply the molar mass of astatine by x and set it equal to 630 grams. 210x=630, solving for x gives you 3 so you know you will need 3 astatine atoms on the right side to balance out the left side.

Posted: **Sun Oct 07, 2018 3:03 pm**

So for this problem you would start out with the information they gave you, which the 9 atoms of Gallium. You would have to first convert the 9 atoms of Ga to grams.

So, (9 atoms Ga)(1 mol Ga/ 6.022 x 10^23 atoms of Ga)(70 g Ga/1 mol Ga) = 1.046 x 10^-21 grams of Ga

Then you would use the grams of Ga, which will also be the mass of At, since you want both sides to be equal, to find the atoms of At

So, (1.046 x 10^-21 grams of At)(1 mol of At/ 210 g of At)(6.022 x 10^23 atoms of At/ 1 mol At) = 3 atoms of At - which is what you would have to add for both sides to be equal.

Hope this helps!

So, (9 atoms Ga)(1 mol Ga/ 6.022 x 10^23 atoms of Ga)(70 g Ga/1 mol Ga) = 1.046 x 10^-21 grams of Ga

Then you would use the grams of Ga, which will also be the mass of At, since you want both sides to be equal, to find the atoms of At

So, (1.046 x 10^-21 grams of At)(1 mol of At/ 210 g of At)(6.022 x 10^23 atoms of At/ 1 mol At) = 3 atoms of At - which is what you would have to add for both sides to be equal.

Hope this helps!

Posted: **Sun Oct 07, 2018 4:42 pm**

you would multiply the actually quantity of gallium you have (9), by the molar mass given 70g/mol. this total will be equal to the molar mass of astatine 210g/mol times the amount of astatine you have. The amount of astatine is unknown so put a variable and then solve for it.

9 x 70 = 210 x A

9 x 70 = 210 x A

Posted: **Sun Oct 07, 2018 7:33 pm**

You would not need to do any tough conversions or math on this one. Molecular weights are given in mol/g. A mole is the same for everything, a mole of elephants is the same as a mole of books, it's just a set reference quantity, don't let it confuse you. So, for this problem, basically, one atom is 3x heavier than the other (in one mol you have an equal amount of each atom, so if you have an equal amount of two things, and one group is three times heavier, each individual thing in the group must be three times heavier). Therefore, you're going to need three times as many light atoms to equal the weight of the heavier atoms to balance the scale.