Massassi Forums Logo

This is the static archive of the Massassi Forums. The forums are closed indefinitely. Thanks for all the memories!

You can also download Super Old Archived Message Boards from when Massassi first started.

"View" counts are as of the day the forums were archived, and will no longer increase.

☖ Forums → Discussion Forum → Anyone good at High School Chemistry?
Anyone good at High School Chemistry?
2006-10-02, 4:46 PM #1
Because it's over my head. Give me A.P. U.S. Gov/Politics/History and I'll get an A. Put me in a General Chemistry class and I get a C.

I need a better understanding of Natural Abundances, such as this problem:

Quote:
The atomic mass of GA is 69.72. There are only two naturally occuriring isotopes of gallium. ^69Ga with a mass of 69.0 and ^71Ga with a mass of 71.0. The natural abundance of the ^69Ga must be approximately:


The answer is 30%, but I have no idea why it is, or how to conclude to that.

(BTW, this is a study guide that the teacher gives to us with all the correct answers...just don't know how to get to them.)

We're also doing molar mass and such...which leads to another problem

Quote:
One gram of TVT, C7H5N3O6, has 7.95 x10^21 nitrogen atoms. How many hydrogen atoms are there in 1.00g of TNT?

Answer: 1.33 x 10^22


:confused:
2006-10-02, 5:21 PM #2
You came here instead of asking me? I'm insulted.

For the first one, atomic mass is the sum of the products of the isotope weights and their relative abundances.

So what you know is that 69.72 = 69.0 * (Abundance of 69Ga) + 71.0 * (Abundance of 71Ga)

You also know that the abundances have to add to 1. So call the first abundance "x" and the second "1-x". Substitute that into the equation. Congratulations, you now have a linear equation in one variable, and if you can't solve that then I think you're beyond my help.

THe second one is even easier. Look at the chemical formula. How many nitrogen atoms does it have? How many hydrogen? What is the ratio of hydrogen to nitrogen? (hint: the answer is 5/3). Multiply this by that big-*** number.
Stuff
2006-10-02, 5:23 PM #3
Originally posted by kyle90:
You came here instead of asking me? I'm insulted.


You wern't on!
2006-10-02, 5:38 PM #4
Well in answer to the first question the answer in your booklet seems pretty clearly wrong to me. For the atomic mass of Gallium to be 69.72 out of a combination of 69 and 71 mass isotopes, it's pretty clearly weighted towards the 69 isotope.
It's a simple simultaneous equation problem basically:
(a) 69x + 71y = 69.72
(b) x + y = 1

Re-arrange (b) into y = 1-x and sub into (a). This boils down to (71-69.72)/2 = x = 0.64.
Therefore the natural abundance of ^69Ga is 64%.

Of course maybe I've totally forgotten A-level chemistry.

As for the second one I don't know the composition of TNT off the top of my head.
2006-10-02, 6:41 PM #5
Inertia is a property of matter. RTFM
"Oh my god. That just made me want to start cutting" - Aglar
"Why do people from ALL OVER NORTH AMERICA keep asking about CATS?" - Steven, 4/1/2009
2006-10-02, 11:12 PM #6
Quote:
Anyone good at High School Chemistry?
Nope.
"it is time to get a credit card to complete my financial independance" — Tibby, Aug. 2009
2006-10-03, 3:52 PM #7
its exactly what everyone else is saying, except i can make it simple.

take the atomic mass of each natural isotope, and multiply it by the relative abundance, then add the numbers together.
Snail racing: (500 posts per line)------@%
2006-10-03, 7:47 PM #8
I hope so, but then again, the more ChME I learn, the more chem I forget.



The occurance of 69 Ga is ~ 60%, and 71 Ga ~ 40%. The math people are showing looks good, the solution manual is just plain wrong.
Yet Another Massassi Map | Sadly I Have a Blog Too
2006-10-03, 8:14 PM #9
Flexor is the best at chemistry.

Right, Flexor?
2006-10-03, 8:15 PM #10
right on!
The music industry is a cruel and shallow money trench where thieves and pimps run free, and good men die like dogs. There's also a negative side.
2006-10-03, 8:15 PM #11
Originally posted by Flexor:
right on!


Wow...it posts!

↑ Up to the top!