How many moles are in 1.00 gram of each of the following substances?

Question

How many moles are in 1.00 gram of each of the following substances?

(a) __________Au

(b)___________ NH3

 

Answer 1

Divide the mass by the molecular weight to get moles.  In the case of Au, divide by the atomic weight.

 

(a)

 

1.00 g of Au

 

Atomic weight of Au ≅ 197 g/mole

 

Number of moles of Au = (1.00 g) / (197 g/mole) ≅ 5.08 x 10^-3 moles

 

(b)

 

1.00 g of NH₃

 

Atomic weight of N ≅ 14.0 g/mole

Atomic weight of H ≅ 1.01 g/mole

 

Molecular weight of NH₃ ≅ 14.0 + 3(1.01) ≅ 17.03 g/mole

 

Number of moles of NH₃ ≅ (1.00 g) / (17.03 g/mole) ≅ 0.0587 moles