nH2= 0,35(mol)

a) PTHH: Mg +  2 HCl -> MgCl2 + H2

x_________2x_______x______x(mol)

PTHH: Fe + 2 HCl -> FeCl2 + H2

y________2y________y_____y(mol)

Ta có hpt: \(\left\{{}\begin{matrix}24x+56y=13,2\\x+y=0,35\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0,2\\y=0,15\end{matrix}\right.\)

b) m=m(muối khan)= mMgCl2 + mFeCl2= 95.x+127y=95.0,2+127.0,15= 38,05(g)

a)

Gọi 

\(n_{Fe} = a(mol) ; n_{Mg} = b(mol)\\ \Rightarrow 56a + 24b = 13,2(1)\)

\(Mg + 2HCl \to MgCl_2 + H_2\\ Fe + 2HCl \to FeCl_2 + H_2\)

Theo PTHH : \(n_{H_2} = a + b = 0,35(mol)\)(2)

Từ (1)(2) suy ra a = 0,15 ;b = 0,2

Vậy : 

\(\%m_{Fe} = \dfrac{0,15.56}{13,2}.100\% = 63,64\%\\ \Rightarrow m_{Mg} = 100\% - 63,64\% = 36,36\%\)

b)

Ta có :\(n_{HCl} = 2n_{H_2} = 0,7(mol)\)

Bảo toàn khối lượng :

\(m_{muối} = m_{kim\ loại} + m_{HCl} - m_{H_2} = 13,2 + 0,7.36,5 - 0,35.2=38,05(gam)\)

Sửa đề: đktc → đkc

a, \(Mg+2HCl\rightarrow MgCl_2+H_2\)

\(Fe+2HCl\rightarrow FeCl_2+H_2\)

Ta có: 24n_Mg + 56n_Fe = 13,2 (1)

\(n_{H_2}=\dfrac{8,6765}{24,79}=0,35\left(mol\right)\)

Theo PT: \(n_{H_2}=n_{Mg}+n_{Fe}=0,35\left(2\right)\)

Từ (1) và (2) \(\Rightarrow\left\{{}\begin{matrix}n_{Mg}=0,2\left(mol\right)\\n_{Fe}=0,15\left(mol\right)\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}\%m_{Mg}=\dfrac{0,2.24}{13,2}.100\%\approx36,36\%\\\%m_{Fe}\approx63,64\%\end{matrix}\right.\)

b, Theo PT: \(\left\{{}\begin{matrix}n_{MgCl_2}=n_{Mg}=0,2\left(mol\right)\\n_{FeCl_2}=n_{Fe}=0,15\left(mol\right)\end{matrix}\right.\)

⇒ m _{muối khan} = 0,2.95 + 0,15.127 = 38,05 (g)

Ap dụng tăng giảm khối lượng

\(n_{MCO_3}=\frac{20,6-18,4}{35,5.2-60}=0,2\)

\(M+60=18,4:0,2=92\Leftrightarrow M=32\)suy ra 2 nguyên tố đó là Mg và Ca

\(Đặt:n_{Mg}=a\left(mol\right);n_{Al}=b\left(mol\right)\left(a,b>0\right)\\ PTHH:Mg+2HCl\rightarrow MgCl_2+H_2\\ 2Al+6HCl\rightarrow2AlCl_3+3H_2\\ \Rightarrow\left\{{}\begin{matrix}24a+27b=5,1\\22,4a+22,4.1,5.b=5,6\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=0,1\\b=0,1\end{matrix}\right.\\ a,\Rightarrow\%m_{Mg}=\dfrac{0,1.24}{5,1}.100\approx47,059\%\\ \Rightarrow\%m_{Al}\approx100\%-47,059\%\approx52,941\%\\ b,n_{HCl}=2.n_{H_2}=2.\left(0,1+0,1.1,5\right)=0,5\left(mol\right)\\ \Rightarrow V_{ddHCl}=\dfrac{0,5}{2}=0,25\left(l\right)\)

a)\(Mg+2HCl\rightarrow MgCl_2+H_2\uparrow\)

   x           2x            x             x

\(2Al+6HCl\rightarrow2AlCl_3+3H_2\)

y            3y          y             1,5y

Ta có hệ:

\(\left\{{}\begin{matrix}24x+27y=5,1\\x+1,5y=\dfrac{5,6}{22,4}=0,25\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0,1\\y=0,1\end{matrix}\right.\)

\(\%m_{Mg}=\dfrac{0,1\cdot24}{5,1}\cdot100\%=47,06\%\)

\(\%m_{Al}=100\%-47,06\%=52,94\%\)

b)\(\Sigma n_{HCl}=2x+3y=2\cdot0,1+3\cdot0,1=0,5mol\)

\(V=\dfrac{n}{C_M}=\dfrac{0,5}{2}=0,25l=250ml\)

\(Đặt:n_{Al}=u\left(mol\right);n_{Fe}=v\left(mol\right)\left(u,v>0\right)\\ n_{H_2}=\dfrac{17,92}{22,4}=0,8\left(mol\right)\\ PTHH:Fe+2HCl\rightarrow FeCl_2+H_2\\ 2Al+6HCl\rightarrow2AlCl_3+3H_2\\ \Rightarrow\left\{{}\begin{matrix}27a+56u=22\\1,5a+u=0,8\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=0,4\\u=0,2\end{matrix}\right.\\ \Rightarrow m_{Al}=0,4.27=10,8\left(g\right);m_{Fe}=56.0,2=11,2\left(g\right)\\ n_{HCl}=2.0,8=1,6\left(mol\right)\\ m_{HCl}=1,6.36,5=58,4\left(g\right)\\ m_{ddHCl}=\dfrac{58,4.100}{25}=233,6\left(g\right)\)

\(2Al+6HCl\rightarrow2AlCl_3+3H_2\)

x           3x             x             1,5x

\(Fe+2HCl\rightarrow FeCl_2+H_2\)

y         2y              y          y

\(\left\{{}\begin{matrix}27x+56y=22\\1,5x+y=\dfrac{17,92}{22,4}\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=0,4\\y=0,2\end{matrix}\right.\)

\(m_{Al}=0,4\cdot27=10,8g\)

\(m_{Fe}=22-10,8=11,2g\)

\(m_{HCl}=36,5\cdot\left(3x+2y\right)=36,5\cdot\left(3\cdot0,4+2\cdot0,2\right)=58,4g\)

\(m_{ddHCl}=\dfrac{m_{HCl}}{C\%}\cdot100\%=\dfrac{58,4}{25\%}\cdot100\%=233,6g\)

Đáp án A

Ta có: MO + H2SO4 ---> MSO4 + H2O 
a a 
MCO3 + H2SO4 ---> MSO4 + H2O + CO2 
b b b 
Chọn b=1 => khối lượng CO2 = 44g => mA = 100g => mMSO4 = 168g 
(M + 16)a + (M + 60)b = 100 (1) 
(M + 96)(a + b) = 168 (2) 
Thế b=1 vào (1) và (2) => a = 0,4 mol ; M = 24 (kim loại Mg) 
%MO = (40*0,4/100)*100= 16% 
%MCO3 = 100% -16% = 84% 

Vậy kim loại 2 là mg và khối lượng hóa học x là 84 %