Chemistry Problem:stoichiometry

Question

 Al+S₈ -->Al₂S₃
-How many moles of aluminum are required to produce 56.9 grams of sulfur?
-5.0 grams of aluminum sulfide is needed. How many grams of sulfur is required to make it?

Answer 1

-How many moles of aluminum are required to produce 56.9 grams of sulfur?

 

The reaction seems to be incorrect. It should be 2Al + 3S --> Al₂S_3.

 

Using the correct chemical equation:

 

1) convert grams of sulfur given (56.9g) to moles using the periodic table weight (32.066g per mol)

 

56.9g*(1 mol S / 32.066g) = 1.774 mol S

 

2) Use the mol-to-mol ratio according to the chemical equation to convert from mol S to mol Al

 

1.774 mol S*(2 mol Al / 3 mol S) = 1.183 mol Al

 

-5.0 grams of aluminum sulfide is needed. How many grams of sulfur is required to make it?

Assuming that the aluminum is present is in EXCESS, we solve this part using the same method as the previous part:

 

1) 5g Al₂S₃ * (1 mol Al₂S₃ / 118 g) * (3 mol S / 1 mol Al₂S₃) * (32g S / 1 mol) = 4g Al₂S₃