how do i find... what is the mass of 9.7 x 10^12 atoms Br?

Answer 1

Do you have a periodic table? Br is atomic element #35 with an atomic weight of 79.9 g/mol Br. If you remember that there are 6.02 x 10^23 atoms/mol (Avogadro's number) you should have enough information to solve the question.

(9.7 x 10^12 atoms Br) x (1 mol Br/6.02 x 10^23 atoms Br) x (79.9 g/mol Br) x (10^9 ng/g) = 1.29 ng

I hope this is right, I haven't done these calculations in awhile. Good luck!

Answer 2

the moles of Br : 9.7*10^12 / 6.02 * 10^23 = 1.6 * 10^-11
the grams of Br : 1.6 * 10^-11 * 80 = 1.29*10^-9