Calculate the mass (in grams) of crystalline Cu (NO3) 2, multiply 3H2O, required to prepare 400g

Calculate the mass (in grams) of crystalline Cu (NO3) 2, multiply 3H2O, required to prepare 400g of a 15% solution of copper (II) nitrate

Given:
m solution (Cu (NO3) 2) = 400 g
ω (Cu (NO3) 2) = 15%

Find:
m (Cu (NO3) 2 * 3H2O) -?

Solution:
1) m (Cu (NO3) 2) = ω (Cu (NO3) 2) * m solution (Cu (NO3) 2) / 100% = 15% * 400/100% = 60 g;
2) n (Cu (NO3) 2) = m (Cu (NO3) 2) / M (Cu (NO3) 2) = 60/188 = 0.32 mol;
3) n (Cu (NO3) 2 * 3H2O) = n (Cu (NO3) 2) = 0.32 mol;
4) m (Cu (NO3) 2 * 3H2O) = n (Cu (NO3) 2 * 3H2O) * M (Cu (NO3) 2 * 3H2O) = 0.32 * 242 = 77.44 g.

Answer: The mass of Cu (NO3) 2 * 3H2O is 77.44 g.