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AS finding relative atomic mass experiment

First chem lesson and I get this...I have to answer some questions on an experiment we did in class. This is a copy of the sheet we have:
https://www.scribd.com/document/199316442/Activity-01-Finding-the-Relative-Atomic-Mass-of-an-Unknowm-Metal-by-Gas-Collection

Hydrogen collected was 141 ml.
Do i do 126/24000 to get moles (moles= vol/24000)
Or do I use this ideal gas rule we just learned? Because we also have this info: Molar gas volume is 24000cm 3 at 298K and 101kPa (RTP).
If so, how do i actually use it?
And then how would I go about finding its Ar?
Thanks for any help.

(edited 7 years ago)

Reply 1

alow

Original post by oshen

Yes.

Or do I use this ideal gas rule we just learned? Because we also have this info: Molar gas volume is 24000cm 3 at 298K and 101kPa (RTP).
If so, how do i actually use it?

You just did.

And then how would I go about finding its Ar?
Thanks for any help.

You would need to know the mass of the gas to get the A_r.

Reply 2

oshen

Original post by alow

Yes.

You just did.

You would need to know the mass of the gas to get the A_r.

Ok so it was 141 ml, not 126, my bad.
If I do 141/24000= 5.875 x 10^-3, thats my moles of hydrogen?
Then the ration of H2 and X are 1:1, so its the same moles of metal x right?

So that leaves this last bit you said :
You would need to know the mass of the gas to get the A_r

How? Also you said I just used the ideal gas rule, but how actually did I?
Thanks

Reply 3

alow

Original post by oshen

Ok so it was 141 ml, not 126, my bad.
If I do 141/24000= 5.875 x 10^-3, thats my moles of hydrogen?
Then the ration of H2 and X are 1:1, so its the same moles of metal x right?

Yes and yes. Now you know the amount of X you started with.

So that leaves this last bit you said :
You would need to know the mass of the gas to get the A_r

If you need to find the A_r of the gas that's what you would need. It wasn't apparent that wasn't what you wanted. Just a tip: don't describe anything as "it" when writing about chemistry, always make it explicitly clear what you're talking about. I know this seems picky and silly, but doing this is really important, especially in exams.

How? Also you said I just used the ideal gas rule, but how actually did I?
Thanks

You used 24dm³ as the volume of one mole of gas at RTP.

Reply 4

oshen

Original post by alow

I was so unclear when I used "it", didn't even realise. Thanks for the advice, I need all I can get for chem xD
I meant the Ar of the metal x, which we used 0.19g, so I would to Ar = mass/mol?

Reply 5

alow

Original post by oshen

I was so unclear when I used "it", didn't even realise. Thanks for the advice, I need all I can get for chem xD
I meant the Ar of the metal x, which we used 0.19g, so I would to Ar = mass/mol?

Using "it" just makes things ambiguous sometimes, which is the last thing you want when you're writing something scientific. There are situations when using "it" is okay, but make sure what you're writing could not be confused in any way.

That's exactly what you would do, as you now know the amount and mass of X.

Reply 6

oshen

Original post by alow

Sorry to keep pestering, one last thing: questions 3 and 4
How would I show the acid was excess in moles, using Ar of X?
If metal x was in lump form? Would you crush it into smaller pieces?

Thank you for all your help :smile:

Reply 7

alow

Original post by oshen

From the chemical equation you can see you need two moles of HCl for every mole of X, so all you need to do is show there is more than twice as much HCl as X.

Yeah, I'd grind it in a mortar and pestle probably.