Chem question please help

Question

Calculate the total number of moles in the following mixture of elements: 54.0 g aluminum sulfide, 6.022•10^24 atoms gallium and 74.2 ml of nitrogen gas (assume at STP)

Answer 1

Aluminum Sulfide = Al₂S₃ 

molar mass = 150 g/mole

moles Al2S3 present in mixture = 54.0 g x 1 mole/150 g = 0.360 moles

moles of Al = 0.360 moles Al2S3 x 2 moles Al/mole Al2S3 = 0.72 moles Al

moles S = 0.360 moles Al2S3 x 3 moles S/mole Al2S3 = 1.08 moles S

 

moles Gallium = 6.022x10^24 atoms x 1 mole Ga/6.022x10^23 atoms  = 10 moles Ga

moles N2 gas at STP = 74.2 ml x 1 L/1000 ml x 1 mol/22.4 L = 0.00331 moles N2

 

Adding up all the moles of the elements, one has 0.720 + 1.08 + 10.0 + 0.00331 = 11.7 moles (to 3 significant figures)