Question

What is the empirical formula for a compound that is comprised of 54.0% sodium, 8.50% boron, and 37.5% oxygen by mass?

A) Na2B2O3.
B) Na3BO3.
C) Na3B2O2.
D) Na4BO4.

Answer 1

B) Na3BO3.

Step-by-step explanation:

Hello!

In this case, since percent compositions are used to identify the empirical formula of an unknown compound, we can assume we have 54.0 g of sodium, 8.50 g of boron and 37.5 g of oxygen, and we compute the moles of each one:

`n_(Na)=54.0g*(1mol)/(23g) =2.35mol\\\\n_B=8.50g*(1mol)/(11g)=0.773mol\\\\n_O=37.5g*(1mol)/(16g)=2.34mol`

Now, we divide by the moles of boron as those are the fewest:

`Na:(2.35)/(0.773)=3\\\\B:(0.773)/(0.773)=1\\\\O=(2.34)/(0.773)=3`

Thus, the empirical formula is B) Na3BO3.

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