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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: 0rion on March 14, 2009, 11:52:59 PM

Title: Significant figures
Post by: 0rion on March 14, 2009, 11:52:59 PM

Significant figures have never made sense to me.

If i have 160 mol of something that has a molar mass of 34.02
Then the number of moles is 5443.2 right

But since its only 3 significant figures does that mean i have to do 5.44xE3 or am i allowed to put more than 3?  :-\

Help anyone?

Title: Re: Significant figures
Post by: Borek on March 15, 2009, 05:03:12 AM

Quote from: 0rion on March 14, 2009, 11:52:59 PM

If i have 160 mol of something that has a molar mass of 34.02
Then the number of moles is 5443.2 right

Wrong. Units, son. UNITS!

Quote from: 0rion on March 14, 2009, 11:52:59 PM

am i allowed to put more than 3?

More then 3 digits you mean? No, your answer contains correct number of digits.

Title: Re: Significant figures
Post by: cliverlong on March 15, 2009, 05:35:45 AM

You have two issues
 
The first is a small slip

mass = moles * formula mass(ak.a. RAM or RMM)

so, as Borek has written your 5443.2 is measured in grams not moles

Secondly, as Borek wrote your approximation is correct, but you have merged two ideas, significant figures and standard form. Have a look at the following that may clarify

http://www.bbc.co.uk/schools/ks3bitesize/maths/number/decimals_3_1.shtml
http://www.bbc.co.uk/schools/ks3bitesize/maths/number/approximation_1.shtml
http://blackboard.tynecoll.ac.uk/nln/frameset.php?url=Science%20And%20Mathematics/Mathematics/act_RB_Standard%20Form/

Clive