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Câu 20)

$\rightarrow$ Chọn $\text{B) 2,7g}$

Ta có PTHH sau:

$\text{2Al+6HCl$\rightarrow$2AlCl3+3H2}$

Có $\text{nH2=$\dfrac{3,36}{22,4}$=0,15 mol}$

Có $\text{nAl=$\dfrac{0,15.2}{3}$=0,1 mol}$

$\rightarrow$ $\text{mAl=n.M=0,1.27=2,7g}$

Câu 21)

$\rightarrow$ Chọn $\text{A) Na, Mg, Zn}$

$\text{K,Ba,Ca,Na,Mg,Al,Zn,Fe,Ni,Sn,Pb,H,Cu,Hg,Ag,Pt,Au}$

$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\text{-}$$\rightarrow$

Chọn $\text{Từ trái sang phải}$

Câu 22)

$\rightarrow$ Chọn $\text{D) H2SO4 đặc,nóng}$

$\text{Cu+2H2SO4(đặc,nóng)$\rightarrow$CuSO4+2H2O+SO2}$

Câu 23)

$\rightarrow$ Chọn $\text{B) Mg}$

Lúc này chỉ có: $\text{ZnSO4}$ tác dụng với $\text{Mg}$

$\text{Mg+ZnSO4$\rightarrow$MgSO4+Zn}$

Sau phản ứng $\text{MgSO4}$ không tác dụng nên đã được $\text{làm sạch}$

Câu 24)

$\rightarrow$ Chọn $\text{A) Al, Zn,Fe}$

$\text{2Al+3Cu(NO3)2$\rightarrow$2Al(NO)3+3Cu}$

$\text{Zn+Cu(NO3)2$\rightarrow$Zn(NO3)2+Cu}$

$\text{Fe+Cu(NO)2$\rightarrow$Fe(NO3)2+Cu}$

Đáp án:

\(\begin{array}{l}
20,B\\
21,A\\
22,D\\
23,B\\
24,A
\end{array}\)

Giải thích các bước giải:

20,

\(\begin{array}{l}
2{\rm{A}}l + 6HCl \to 2{\rm{A}}lC{l_3} + 3{H_2}\\
{n_{{H_2}}} = 0,15mol\\
 \to {n_{Al}} = \dfrac{2}{3}{n_{{H_2}}} = 0,1mol\\
 \to {m_{Al}} = 2,7g
\end{array}\)

22, \(Cu + 2{H_2}S{O_4} \to CuS{O_4} + S{O_2} + 2{H_2}O\)

23, \(Mg + ZnS{O_4} \to Mg{\rm{S}}{O_4} + Zn\)

Lọc bỏ kim loại Zn ta được mẫu \(Mg{\rm{S}}{O_4}\) tinh khiết 

24,

\(\begin{array}{l}
2Al + 3Cu{(N{O_3})_2} \to 2Al{(N{O_3})_3} + 3Cu\\
Zn + Cu{(N{O_3})_2} \to Zn{(N{O_3})_2} + Cu\\
F{\rm{e}} + Cu{(N{O_3})_2} \to F{\rm{e}}{(N{O_3})_2} + Cu
\end{array}\)