# Chemical Forums

## Chemistry Forums for Students => High School Chemistry Forum => Topic started by: gt5hz on October 17, 2009, 12:30:32 AM

Title: Is concentration an exact number or a measured value?
Post by: gt5hz on October 17, 2009, 12:30:32 AM
Let's say the subtance being referred to was prepared by a senior high school chem teacher or even chemists.

I know that it is equal to number moles/volume solution, so therefore it comes from measured values. But can 0.2M of say Fe(NO3)3 be written as 0.20M for the purpose of making the value more specific for calculations involving significant digits? Can I not assume that chemists/the teacher did a precise job of making it and say 0.20M instead of 0.2M?
Title: Re: Is concentration an exact number or a measured value?
Post by: Borek on October 17, 2009, 05:46:20 AM
If it is written as 0.2 M it is usually understood that concentration can be anything between 0.15 and 0.2499999, while 0.20M means anything between 0.195 and 0.204999999. Labelling 0.2M solution as 0.20M solution is an error.