Câu 3:
$\overline{M}_{hh}=0,5.16=8$
Xét $1$ mol hỗn hợp.
$\Rightarrow m_{hh}=8.1=8g$
$n_A=25\%n_{hh}=0,25(mol)$
$\Rightarrow n_{H_2}=1-0,25=0,75(mol)$
Ta có:
$0,25M_A+0,75.2=8$
$\Leftrightarrow M_A=26$
Câu 4:
$\dfrac{M_A}{M_B}=2$
$\Leftrightarrow M_A=2M_B$
$n_{hh}=\dfrac{1,568}{22,4}=0,07(mol)$
$\Rightarrow \dfrac{1,68}{M_A}+\dfrac{1,12}{M_B}=0,07$
$\Leftrightarrow \dfrac{1,68}{2M_B}+\dfrac{1,12}{M_B}=0,07$
$\Leftrightarrow M_B=28$
$\to M_A=28.2=56$
