2% H = 4.1/1 = H4
46%O = 94.3/16 = O6
Looks like B to me
What is the molecular formula of a compound with percent composition 26% aluminum, 27% silicon,46% oxygen and 2% hydrogen and a molar mass of 205 g/mol?
A) Al53si55O94H4
B) Al2Si206H4
C) Alsi203h4
D) ALSiO3H2
2 answers
@oobleck. This procedure I've never seen before. Time wise it sure speeds up the calculated answer. It works because of two approximations plus a luxury we allow ourselves.
1. We assume the molar mass of 205 is correct. It is not 205 but it's close.
2. Since the molar mass is just close, then we don't get EXACT whole number so we fudge a little, call that some word(s) that excuses us (experimental error comes to mind), and
3. Use the luxury of rounding up or down to make a whole number which often stretches the boundary of what we can call experimental error.
We can't get away with the excuse for high accuracy. Only a few of those atomic masses in the periodic table come from a chemist anyway. Mass spectrometry beats chemical every day of the week for those values in the periodic table.
1. We assume the molar mass of 205 is correct. It is not 205 but it's close.
2. Since the molar mass is just close, then we don't get EXACT whole number so we fudge a little, call that some word(s) that excuses us (experimental error comes to mind), and
3. Use the luxury of rounding up or down to make a whole number which often stretches the boundary of what we can call experimental error.
We can't get away with the excuse for high accuracy. Only a few of those atomic masses in the periodic table come from a chemist anyway. Mass spectrometry beats chemical every day of the week for those values in the periodic table.
1 answer