30/
$PTPƯ:$
$Zn+H_2SO_4\xrightarrow{} ZnSO_4+H_2↑$ $(1)$
$CuO+H_2\xrightarrow{t^o} Cu+H_2O$ $(2)$
$n_{Zn}=\dfrac{13}{65}=0,2mol.$
$Theo$ $pt1:$ $n_{H_2}=n_{Zn}=0,2mol.$
$n_{CuO}=\dfrac{20}{80}=0,25mol.$
$\text{Lập tỉ lệ:}$ $\dfrac{0,25}{1}>\dfrac{0,2}{1}$
$Theo$ $pt:$ $n_{Cu}=n_{H_2}=0,2mol.$
$⇒m_{Cu}=0,2.64=12,8g.$
31/
$a,PTPƯ:2Al+6HCl\xrightarrow{} 2AlCl_3+3H_2↑$
$n_{HCl}=\dfrac{21,9}{36,5}=0,6mol.$
$Theo$ $pt:$ $n_{Al}=\dfrac{1}{3}n_{HCl}=0,2mol.$
$⇒m_{Al}=0,2.27=5,4g.$
$Theo$ $pt:$ $n_{H_2}=\dfrac{1}{2}n_{HCl}=0,3mol.$
$⇒V_{H_2}=0,3.22,4=6,72l.$
$b,Theo$ $pt:$ $n_{AlCl_3}=\dfrac{1}{3}n_{HCl}=0,2mol.$
$⇒m_{AlCl_3}=0,2.133,5=26,7g.$
chúc bạn học tốt!