13. earth's surface area is 5.1 x 10^8 km², its crust has an average thickness of 35 km and an average density of 2.8 g/cm'. the two rarest (non-radioactive) elements in the crust are ruthenium and rhodium, each with an abundance of 1.0 x 10g/metric ton crust. what is the total mass of these two elements in the earth's crust? (1g = 1 x 10 metric ton)

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.

am i too late?

explanation: