[cmaslk]

I have a problem that I can solve in two ways, each of which lead to different answers, and would like an opinion on which is more justified.

Consider the reaction

Al₂S₃ + 6HCl → 2AlCl₃ + 3H₂S .

How much AlCl₃ can be formed from 109.35g HCl?

• not enough information
• six moles
• one mole
• two moles
• twelve moles
• three moles
• four moles

Assuming you have Al₂S₃ in excess, the answer would be [3. one mole], because

[tex]\mathrm{109.35g\,HCl \times \frac{1\,mol\,HCl}{36.46\,g\,HCl} \times \frac{2\,mol\,AlCl_{3}}{6\,mol\,HCl}\approx1\,mol\,AlCl_{3}}[/tex].


However, I don't feel that would be correct because the problem doesn't tell you to treat Al₂S₃ as an excess reactant. Since you might have a limiting amount of it, you might not be able to fully react all of the HCl.

Therefore [1. not enough information] would be the answer.


Should I treat Al₂S₃ as an excess reactant even though it's not stated as such by the problem? If so, is this something that a chemistry student would always assume in similar problems i.e. is this the way things are done in chemistry?

[Borek]

Should I treat Al₂S₃ as an excess reactant even though it's not stated as such by the problem? If so, is this something that a chemistry student would always assume in similar problems i.e. is this the way things are done in chemistry?

Yes, when you are told how much of one reactant you have it means you are to assume everything else is in excess (unless these other amounts are also explicitly given).

[Schrödinger]

I guess the question whould be : What is the maximum amount of AlCl₃ you can obtain from ... But yeah, you assume the other reactant to be in excess for maximum yield calculation

[cmaslk]

Thank you! The ambiguity of the problem (for someone with limited chemistry experience) really threw me.

[Mitch]

@cmaslk You did a wonderful job on the problem. I think you'll do just fine in this class.