Chemistry - using conversion factors in Stochiometry questions

[Aletheia]

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So this is a pretty basic question from a textbook. So, the question is "An HCl solution consists of 28% HCl by mass and has a density of 1.14g/ml. What volume of this solution is required to react completely with 1.87g Al in the following reaction:

2Al+6HCl--> 2AlCl3+3H2

This solution is:
1.87gAl*moleAl/26.98gAl x 6mol HCL/2mlAl x 36.46gHCl/1ml HCl x 100gHCl/28 g HCl x 1 ml HCl/1.14g HCl

So, although I can do these questions without too many problems, I do have one issue: the conversion factor of 100g/28 g HCl. I understand why we need to use this conversation factor, but I always, without thinking, reverse it and make it 28g/100g. So, I was wondering if someone could please reason out how to know which way to have the conversion factor (yes, I am awful at math).

Thanks.

 

[PiBond]

Whenever I see % in a stoichiometry problem I always think "% out of 100"--so in this case, you would have 28 grams HCl per 100 grams of solution. You can also reason out which to put on top by looking at units and seeing what you need to cancel out.

I'm looking at your dimensional analysis solution and wondering if it's supposed to read: "100g/(28g HCl)" instead of having HCl on top and bottom?

 

[Aletheia]

Okay, I think that makes sense. I guess since they're both grams I find it confusing, but since the 28g is what I am working with it makes sense I'd cancel with that.

Very astute! Yes, it should be 100g HCl solution. It has been far too long since basic Chem.