July 24th, 2018, 02:17 AM  #1 
Member Joined: Aug 2016 From: South Korea Posts: 53 Thanks: 0  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 
July 24th, 2018, 03:34 AM  #2 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,302 Thanks: 935 
Ask your teacher....

July 24th, 2018, 09:29 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 19,712 Thanks: 1806  
July 24th, 2018, 09:32 AM  #4 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,879 Thanks: 1087 Math Focus: Elementary mathematics and beyond  
July 24th, 2018, 10:19 AM  #5  
Senior Member Joined: May 2016 From: USA Posts: 1,148 Thanks: 479  Quote:
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 $C_{14}H_{18}N_{2}O_5.$  
July 24th, 2018, 10:21 AM  #6 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,302 Thanks: 935  
July 24th, 2018, 10:30 AM  #7 
Global Moderator Joined: Oct 2008 From: London, Ontario, Canada  The Forest City Posts: 7,879 Thanks: 1087 Math Focus: Elementary mathematics and beyond  
July 24th, 2018, 10:48 AM  #8 
Senior Member Joined: Jun 2015 From: England Posts: 887 Thanks: 266 
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. 
July 24th, 2018, 11:22 AM  #9 
Math Team Joined: Oct 2011 From: Ottawa Ontario, Canada Posts: 13,302 Thanks: 935  
July 24th, 2018, 01:17 PM  #10 
Math Team Joined: May 2013 From: The Astral plane Posts: 1,889 Thanks: 768 Math Focus: Wibbly wobbly timeywimey stuff.  

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