\(Al;Cu\Rightarrow Al\left(NO_3\right)_3;Cu\left(NO_3\right)_2\underrightarrow{t^o}Al_2O_3;CuO\)
\(n_{Al_2O_3}=\dfrac{1}{2}n_{Al}=\dfrac{1}{2}\cdot0,02=0,01mol\)
\(n_{CuO}=n_{Cu}=0,03mol\)
\(\Rightarrow m_{rắn}=m_{Al_2O_3}+m_{CuO}=0,01\cdot102+0,03\cdot80=3,42\left(g\right)\)