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July 24th, 2018, 02:17 AM   #1
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Question Empirical Formula

What do they mean by '"too far to round" here? Can't that be rounded and just be 3? Did I miss something (like a rule or something?) in my chemistry class about that kind of number being 'too far to round'? if I did, can someone explain to me when should I multiply each solution to the same factor?

too far too round.jpg
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July 24th, 2018, 03:34 AM   #2
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Ask your teacher....
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July 24th, 2018, 09:29 AM   #3
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Originally Posted by SlayedByMath View Post
Can't that be rounded . . .
I'm not sure what you are referring to as "that".

All that's meant is that you shouldn't "round" the ratio 3.6:0.6 to 4:1 if the appropriate ratio is 6:1.
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July 24th, 2018, 09:32 AM   #4
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Ask your teacher....
That's not always a practical alternative.
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July 24th, 2018, 10:19 AM   #5
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Quote:
Originally Posted by SlayedByMath View Post
What do they mean by '"too far to round" here? Can't that be rounded and just be 3? Did I miss something (like a rule or something?) in my chemistry class about that kind of number being 'too far to round'? if I did, can someone explain to me when should I multiply each solution to the same factor?

Attachment 9816
It is not pure math. The context is the atomic theory. The number of each type of atom in a single molecule is, according to the atomic theory, supposed to be an integer. You have, however, experimental data, which will not be exact.

So first they do the indicated arithmetic on the experimental results and get approximate answers of 4.76, 6.10, 0.68, and 1.70. These are not expected to be integers because they do not represent a single molecule. Nevertheless, we expect the ratios among them to reflect the numbers of different types of atom in each molecule (subject to experimental error).

So they take ratios relative to the smallest number, which is 0.68: this is essentially a preliminary hypothesis that there is only one atom of this element in each molecule. They hope to get numbers that are very close to integers for all the elements. When they divide by 0.68, they get quotients very close to integers except in one case. They now ask what integer they must multiply all the quotients by to get integers in each case. In this case it is 2.

It is a mistake to call it rounding. When they get an answer of 8.97 expecting an integer, they attribute the 0.03 to experimental error and correct the answer to 9. But if the difference is too large to attribute to experimental error, they say that such a correction is improper.

They come up with a formula of $C_{14}H_{18}N_{2}O_5.$
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July 24th, 2018, 10:21 AM   #6
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That's not always a practical alternative.
True; but stated is "in my chemistry class"....
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July 24th, 2018, 10:30 AM   #7
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True; but stated is "in my chemistry class"....
I think what I stated still holds.
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July 24th, 2018, 10:48 AM   #8
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A pretty good explanation Jeff.

The only thing I'd add is a request to the OP to show the full question next time to stop everybody having to guess what was going on.
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July 24th, 2018, 11:22 AM   #9
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I think what I stated still holds.
If you don't think the same as I do, then you're wrong
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July 24th, 2018, 01:17 PM   #10
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If you don't think the same as I do, then you're wrong
Nobody thinks like you, Denis.

-Dan
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