Answer:
[tex]\boxed {\boxed {\sf 0.261 \ mol \ B}}[/tex]
Explanation:
We are asked to find the number of moles in a sample of 2.82 grams of boron.
We convert grams to moles using the molar mass or the mass of 1 mole of a substance. These values are found on the Periodic Table. They are equivalent to the atomic masses, but the units are grams per mole instead of atomic mass units.
Look up the molar mass of boron (B).
Convert using dimensional analysis. Set up a conversion factor using the molar mass.
[tex]\frac {10.81 \ g \ B}{ 1 \ mol \ B}[/tex]
We are converting 2.82 grams of boron to moles, so we multiply by this value.
[tex]2.82 \ g \ B *\frac {10.81 \ g \ B}{ 1 \ mol \ B}[/tex]
Flip the ratio so the units of grams of boron cancel.
[tex]2.82 \ g \ B *\frac { 1 \ mol \ B}{10.81 \ g \ B}[/tex]
[tex]2.82*\frac { 1 \ mol \ B}{10.81}[/tex]
[tex]\frac {2.82}{10.81} \ mol \ B[/tex]
[tex]0.2608695652 \ mol \ B[/tex]
The original value of grams has 3 significant figures, so our answer must have the same. For the number we found, this is the thousandth place. The 8 in the ten-thousandth place tells us to round the 0 up to a 1.
[tex]0.261 \ mol \ B[/tex]
There are approximately 0.261 moles of boron (B)in 2.82 grams of boron.
