Question

How many grams of water do you need to prepare a 25% salt solution if the mass of salt is 100g?

Answer 1

Answer:

The key is to recognize the percentage concentration is mass of solute divided by mass of solution, not the original solvent.

If you add x grams of salt, the solution has a mass of 250 g + x

x/(250 g + x) = 0.15

x = 250 g * 0.15/0.85 = 44.12 g (rounded)

Check 44.12/294.12 = 0.150007, close enough, given rounding.

(While 0.15/0.85 reduces to 3/17, I still can’t do it in my head)