\(n_{BaCO_3}=\dfrac{5,94}{197}=0,03\left(mol\right)\)
PTHH : \(\dfrac{Ba\left(OH\right)_2}{0,03\left(mol\right)}+CO_2\rightarrow\dfrac{BaCO_3\downarrow}{0,03\left(mol\right)}+H_2O\)
\(\Rightarrow C_{M\left(Ba\left(OH\right)_2\right)}=\dfrac{0,03}{0,2}=0,15\left(M\right)\)
\(\dfrac{BaCO_3}{0,03\left(mol\right)}-^{t^o}->\dfrac{BaO}{0,03\left(mol\right)}+CO_2\)
\(\Rightarrow m_{BaO}=153.0,03=4,59\left(g\right)\)