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.

 

[DeeNos]

Yes, your calculation is correct. To convert from ppm to mg/L, you simply multiply by 1. This means that 0.5ppm is equivalent to 0.5mg/L. Since you want to know how many grams of A are needed for 20 liters of water, you need to convert mg/L to grams by multiplying by the volume (20 liters). This gives you a total of 10mg of A needed. However, since only 10% of A becomes C, you will need 10 times that amount, which is 100mg of A. Keep in mind that this is just a rough estimate and the actual amount of A needed may vary depending on the solubility and other factors. It is always best to double check your calculations and make sure they make sense in the context of the problem.