Question

A garden fertilizer contains 15% by mass of nitrogen. The recommended usage is 30g of fertilizer per 10dm^3 of water. What is the concentration of nitrogen in this solution?
a)0.15 g dm^-3
b)0.30 g dm^-3
c)0.45 g dm^-3
d)3.00 g dm^-3

Answer 1

15% by mass means 15 g N/100g fertilizer or 0.15 g N/g fertilizer.
So 30 g fertilizer has 30 x 0.15 = 4.50g N. You put this in 10 dm^3 so the concn is
4.50g/10dm^3 = 0.45 g/dm^3