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# Couple of questions from AQA Chem paper watch

1. Hi! I've just done the CHEM1 paper from June 15, and have a few questions - thought I'd ask on here before taking any to my tutor

1) firstly in pV=nRT is n the moles of gas produced? - I'm pretty sure it is I just wanted to clarify!

2) if you are told that something has 95% yield, do you multiply the original moles/mass by 100/95? I was doing this later in my method but it seems that on mark schemes they do this as the first step?

3) How to work out the number of electrons on the azide ion, N3 ^- (so overall charge of -1)?
I did 3 x 14 which is 42 and added 1 for the negative charge, which gave me a total of 43. But the answer is 44 and I'm not sure where the extra electron came from?

4) And finally, how do you work out the formula of magnesium azide? The azide being the N3^- ion
How would the negative charge impact the formula? The correct answer is MgN6 just not sure how they get there

Thanks so much if anyone can help with any of these
2. 1) yes, n is the moles
4) So am Mg ion has a 2+ charge. Since N3 has a singular -1 charge, you'd need 2 N3 for every Mg if that makes sense.
Sorry I didn't answer the other two, am too lazy to read haha
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3. (Original post by LilN)
1) yes, n is the moles
4) So am Mg ion has a 2+ charge. Since N3 has a singular -1 charge, you'd need 2 N3 for every Mg if that makes sense.
Sorry I didn't answer the other two, am too lazy to read haha
Thank you and haha no problem! Can I just clarify n is the moles of GAS only? So if you had other solid products they're not included?
4. (Original post by jazz_xox_)
Thank you and haha no problem! Can I just clarify n is the moles of GAS only? So if you had other solid products they're not included?
No problem haha, yeah it's the moles of the gas only! I don't think I've ever come across a question that has solid products or that requires you to exclude solid products so wouldn't worry about that too much. About question 3 though, you've been asked to work out the number of electrons in the azide ion, shouldn't you be doing 3 x 7 since 14 is the mass of a nitrogen atom, not the amount of electrons it has? Which then questions why the answer is 44 haha
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5. (Original post by LilN)
No problem haha, yeah it's the moles of the gas only! I don't think I've ever come across a question that has solid products or that requires you to exclude solid products so wouldn't worry about that too much. About question 3 though, you've been asked to work out the number of electrons in the azide ion, shouldn't you be doing 3 x 7 since 14 is the mass of a nitrogen atom, not the amount of electrons it has? Which then questions why the answer is 44 haha
Okay thanks, on a question I just did it required the moles of gas separate from solid products, I'd never seen that before either!

Ohh yes of course you would use 7!! I was thinking in terms of Mr, thank you

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