Calculate the mass of copper oxide (2) formed during the decomposition of copper hydroxide (3).

Given:
m (Cu (OH) 2) = 49 g

Find:
m (CuO) -?

1) Write the reaction equation:
Cu (OH) 2 => CuO + H2O;
2) Calculate the molar mass of Cu (OH) 2:
M (Cu (OH) 2) = Mr (Cu (OH) 2) = Ar (Cu) * N (Cu) + Ar (O) * N (O) + Ar (H) * N (H) = 64 * 1 + 16 * 2 + 1 * 2 = 98 g / mol;
3) Calculate the amount of substance Cu (OH) 2:
n (Cu (OH) 2) = m (Cu (OH) 2) / M (Cu (OH) 2) = 49/98 = 0.5 mol;
4) Determine the amount of substance CuO:
n (CuO) = n (Cu (OH) 2) = 0.5 mol;
5) Calculate the molar mass of CuO:
M (CuO) = Mr (CuO) = Ar (Cu) * N (Cu) + Ar (O) * N (O) = 64 * 1 + 16 * 1 = 80 g / mol;
6) Calculate the mass of CuO:
m (CuO) = n (CuO) * M (CuO) = 0.5 * 80 = 40 g.

Answer: The mass of CuO is 40 g.