Calculate the molecular weights for NH 3 and SF 6 .

Question

How many grams of  are needed to provide the same number of molecules as in  g 

Answer 1

I assume the question is

How many grams of NH₃ are needed to provide the same number of molecules as in 0.75 g of SF₆

Use periodic table to find atomic weights of elements.

Molecular weight of SF₆ = atomic weight of S + 6 x atomic weight of F = 32.066 + 6 x 18.998 = 146.05 grams

Molecular weight of NH₃ = atomic weight of N + 3 x atomic weight of H = 14.007 + 3 x 1.008 = 17.03 grams

Number of molecules of compound = Avogadro's number x weight of compound / molecular weight of compound

Avogadro's number A = 6.022 x 10²³

Molecules of NH₃ = Molecules of SF₆

A x Weight of NH₃ / Molecular Weight of NH_{3 =} A x Weight of SF₆ / Molecular Weight of SF₆

Cancel A from both sides and rearrange to get

Weight of NH₃ = (Weight of SF₆ / Molecular Weight of SF₆) x Molecular Weight of NH₃ 

= (0.75 / 146.05) x 17.03 = 0.09 grams

Weight of NH₃ needed is 0.09 grams