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# Cambridge Chemistry Challenge watch

1. Help with Rg...I don't know what I'm doing wrong...
2. what does he wants in Rg? I didnt understand the 'O-17 O-18'
Its 1atm? and the temperature?
Help with Rg...I don't know what I'm doing wrong...
same! LOL. confusing me!!
4. (Original post by Randophera)
I have to say, this challenge wasn't bad. But Rg is a little misleading at first. Did they have to use a minus sign? O2 doesn't even have single bonds! Honestly cambridge could've been less sneaky and have used an equals sign instead.
I've just twigged that it meant a molecule with 1 atom 17 and 1 atom 18. I thought it meant the mass of oxygen-17 and oxygen-18.

It made no difference, I just got rid of the moles of 16 and used what was left.

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5. Is it Iron on Silver? I'm going crazy
6. do I consider 1atm, 298K and %O2=21%? And the molecular mass of O2?
7. Finished

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8. So I'm doing Rg. I've worked out the volume by [50*(365/2)*(365/2)*4pi/3]/2 and multiplied by 22400 to find the number of moles of gas. Then I multiplied by 0.21 to find the amount of oxygen, then by the relative abundance of each isotope and finally by the RMM of 17-O=18-O but I don't get the right answer. Where have I gone wrong?
9. I need help with gold
10. Rg is confusing me. Can someone help please? I'm confused about the abundancy of 18O=17O. How do I work this out?
11. (Original post by TheNoobyPotato)
Rg is confusing me. Can someone help please? I'm confused about the abundancy of 18O=17O. How do I work this out?
I worked it out by abundance of 18O*abundance of 17O, though I haven't managed to get the right answer overall yet.
12. (Original post by Ferrarifan 27)
I worked it out by abundance of 18O*abundance of 17O, though I haven't managed to get the right answer overall yet.
That's what I did but it failed

0.2% X 0.0377121?
13. (Original post by TheNoobyPotato)
That's what I did but it failed
I've just thought - maybe multiply by 2 as well, because it could be 17O-18O or 18O-17O
14. (Original post by Ferrarifan 27)
I've just thought - maybe multiply by 2 as well, because it could be 17O-18O or 18O-17O
Dude, I don't even understand why you times it by 2 because it's 4am where I am. But it worked anyway, thanks so much.

EDIT: it's 3am, not 4am. Shows how tired I am I suppose!!
15. the ''-'' is a bond or a subtraction?
16. (Original post by TheNoobyPotato)
Dude, I don't even understand why you times it by 2 because it's 4am where I am. But it worked anyway, thanks so much.

Yeah, I still don't get the right answer: I've worked out the volume by [50*(365/2)*(365/2)*4pi/3]/2 and multiplied by 22400 to find the number of moles of gas. Then I multiplied by 0.21 to find the amount of oxygen, then by 3.81×10^−4*2.0514×10^−3 for the relative abundance and finally by the RMM of 17-O=18-O*2 so where have I gone wrong?
17. (Original post by lpdsr)
the ''-'' is a bond or a subtraction?
bond
18. (Original post by Ferrarifan 27)
Yeah, I still don't get the right answer: I've worked out the volume by [50*(365/2)*(365/2)*4pi/3]/2 and multiplied by 22400 to find the number of moles of gas. Then I multiplied by 0.21 to find the amount of oxygen, then by 3.81×10^−4*2.0514×10^−3 for the relative abundance and finally by the RMM of 17-O=18-O*2 so where have I gone wrong?
Hmm, that's not what I did. I'll PM you!
19. Ok, so the the amount of moles of O2 (all types) is 38300417,17 moles?
20. can anybody help me? im stuck in Rg for more than 1 hour!

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