a) \(n_{NaOH}=\dfrac{20}{40}=0,5\left(mol\right)\)
PTHH: CuCl2 + 2NaOH --> Cu(OH)2 + 2NaCl
Xét tỉ lệ: \(\dfrac{0,2}{1}< \dfrac{0,5}{2}\) => CuCl2 hết, NaOH dư
PTHH: CuCl2 + 2NaOH --> Cu(OH)2 + 2NaCl
0,2------>0,4-------->0,2------->0,4
Cu(OH)2 --to--> CuO + H2O
0,2-------------->0,2
=> mCuO = 0,2.80 = 16(g)
b)
\(\left\{{}\begin{matrix}m_{NaOH\left(dư\right)}=20-0,4.40=4\left(g\right)\\m_{NaCl}=0,4.58,5=23,4\left(g\right)\end{matrix}\right.\)