Why am I getting this wrong? How many mols of molecules are in #8.90 xx 10^47 "molecules"#? I am getting #1.47 xx 10^(70)#.

1 Answer
Truong-Son N.
Sep 28, 2015

Well:

#8.90xx10^47 cancel"molecules" xx ("1 mol")/(6.0221413xx10^23 cancel"molecules")#

#= color(blue)(1.48xx10^24 "mols")#

Notice that the exponent was subtracted because of the rule of exponents that says you subtract the exponents of the numbers you divide. #\mathbf ((a^x)/(a^y) = a^(x-y))#.

The purpose of the #"mol"# is to have an atomic mass unit (amu) that lets you write a large quantity as a smaller one. Instead of:

"#6.0221413xx10^23 "things"#"

...we write "#"1 mol of things"#".

If you convert from molecules to #"mols"# and somehow get a larger number, you've done something wrong.

Related questions
Impact of this question
78 views around the world
You can reuse this answer
Creative Commons License