Convert ppm to mg/L - Calculate Grams of A Needed

[Cypher49]

Homework Statement

A is a stable powder
B is water
C is the product of the powder being in contact with water.

A is soluble in substance B and for every gram of A 10% is C.

For a concentration of 0.5ppm of C in twenty liters of water how many grams of A do you need?

The Attempt at a Solution

I went on the assumption that ppm=mg/l.
So 0.5ppm=0.5mg/l, and I would need 10mg for the twenty liters
Which means that I would need 100mg of A.

Is this correct?

 

[Borek]

I would need 100mg of A.

Is this correct?

That would be my answer as well, although I find the wording of the question confusing.

 

[Cypher49]

Thanks for the confirmation, I'm just replying to say that 100mg was indeed the correct answer.

If you don't mind me asking, how did the wording confuse you?

 

[Borek]

If 0.1g of A reacted with water, what is mass of the product? Again 0.1g? Not impossible, but counterintuitive, at least to me.