Question

Hi. I am having a problem setting this one up. I like to use dimensional analysis. Determine the mass in grams of 3.00 × 10²¹ atoms of arsenic. (The mass of one mole of arsenic is 74.92 g.)

Answer 1

To solve this problem we have to use Avogadros number that states that a mole of any element or compound has 6.022e23 atoms or molecules.

The first step is to determine how many moles are there in 3.00e21 atoms of arsenic:

$3.00\times10^{21}atoms\cdot\frac{1mol}{6.022\times10^{23}atoms}=4.98\times10^{-3}mol$

Now, use the molecular weight to determine the mass of the obtained number of moles:

$4.98\times10^{-3}mol\cdot\frac{74.92g}{1mol}=0.37g$

The mass is 0.37g of arsenic.