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\(a,\left(1\right)Fe_2O_3+3H_2\rightarrow2Fe+3H_2O\left(1:3:2:3\right)\)
\(\left(2\right)Mg+2HCl\rightarrow MgCl_2+H_2\left(1:2:1:1\right)\\ \left(3\right)2FeCl_3+3Ca\left(OH\right)_2\rightarrow2Fe\left(OH\right)_3+3CaCl_2\left(2:3:2:3\right)\)
\(\left(4\right)K_2CO_3+2HCl\rightarrow2KCl+H_2O+CO_2\left(1:2:2:1:1\right)\)
\(b,PTHH:2Cu+O_2\underrightarrow{t^o}2CuO\\ Áp.dụng.ĐLBTKL,ta.có:\\ m_{Cu}+m_{O_2}=m_{CuO}\\ m_{O_2}=m_{CuO}-m_{Cu}=32-25,6=6,4\left(g\right)\)
\(3Fe + 2O_2 \xrightarrow{t^o} Fe_3O_4\\ Fe + 4HNO_3 \to Fe(NO_3)_3 + NO + 2H_2O\\ 2Fe + O_2 \xrightarrow{t^o} 2FeO\\ FeO + 2HCl \to FeCl_2 + H_2O\\ 2FeCl_2 +Cl_2 \to 2FeCl_3\\ FeCl_3 + 3KOH \to Fe(OH)_3 + 3KCl\\ 2Fe + 6H_2SO_4 \to Fe_2(SO_4)_3 + 3SO_2 +6 H_2O\)
\(2Al\left(OH\right)_3\rightarrow Al_2O_3+3H_2O\left(2:1:3\right)\)
\(2C_2H_2+5O_2\rightarrow4CO_2+2H_2O\left(2:5:4:2\right)\)
\(Ba+2H_2O\rightarrow Ba\left(OH\right)_2+H_2\left(1:2:1:1\right)\)
\(CH_4+2O_2\rightarrow CO_2+2H_2O\left(1:2:1:2\right)\)
\(3Fe + 2O_2 \xrightarrow{t^o} Fe_3O_4\\ Fe_3O_4 + 8HCl \to 2FeCl_3 + FeCl_2 + 4H_2O\\ FeCl_2 + 2KOH \to Fe(OH)_2 + 2KCl\\ 2Fe(OH)_2 + \dfrac{1}{2}O_2 + H_2O \to 2Fe(OH)_3\\ 2Fe(OH)_3 \xrightarrow{t^o} Fe_2O_3 + 3H_2O\)
Bài 5:
\(1:4Al+3O_2\underrightarrow{t^o}2Al_2O_3\)
2: \(2Al\left(OH\right)_3\underrightarrow{t^o}Al_2O_3+3H_2O\)
\(3:Al_2O_3+6HCl\rightarrow2AlCl_3+3H_2O\)
4: \(2Al+6HCl\rightarrow2AlCl_3+3H_2\uparrow\)
5: \(CH_4+2O_2\underrightarrow{t^o}CO_2+2H_2O\)
6: \(Fe+2HCl\rightarrow FeCl_2+H_2\uparrow\)
7: \(K_2O+H_2O\rightarrow2KOH\)
8: \(2Na+2H_2O\rightarrow2NaOH+H_2\uparrow\)
9: \(2Fe+3Cl_2\underrightarrow{t^o}2FeCl_3\)
10: \(CaCl_2+Na_2CO_3\rightarrow CaCO_3\downarrow+2NaCl\)
\(P_2O_5+3H_2O\rightarrow2H_3PO_4\) (1:3:2)
\(2C_2H_2+5O_2\xrightarrow[]{t^o}4CO_2+2H_2O\) (2:5:4:2)
\(2Fe\left(OH\right)_3\xrightarrow[]{t^o}Fe_2O_3+3H_2O\) (2:1:3)
\(4Na+O_2\rightarrow2Na_2O\) (4:1:2)
\(2Mg+O_2\xrightarrow[]{t^o}2MgO\) (2:1:2)
\(2Fe+3Cl_2\xrightarrow[]{t^o}2FeCl_3\) (2:3:2)
\(Mg+2HCl\rightarrow MgCl_2+H_2\) (1:2:1:1)
\(2C_4H_{10}+13O_2\xrightarrow[]{t^o}8CO_2+10H_2O\) (2:13:8:10)
\(3NaOH+AlCl_3\rightarrow3NaCl+Al\left(OH\right)_3\) (3:1:3:1)
\(3Cu+8HNO_3\rightarrow3Cu\left(NO_3\right)_2+2NO+4H_2O\) (3:8:3:2:4)
Đáp án D
Phản ứng có phương trình ion rút gon 
là: (1); (2); (3); (6); (8).
(4) BaSO3 + 2H+ + SO42- → BaSO4 + CO2 + H2O.
(5) 2NH4+ + SO42- + Ba2+ + 2OH- → BaSO4 + 2NH3 + 2H2O.
(7) Fe2+ + SO42- + Ba2+ + 2OH- → Fe(OH)2 + BaSO4.
Đáp án D
Phản ứng có phương trình ion rút gon S O 4 2 - + B a 2 + → B a S O 4 là: (1); (2); (3); (6); (8).
(4) BaSO3 + 2H+ + SO42- → BaSO4 + CO2 + H2O.
(5) 2NH4+ + SO42- + Ba2+ + 2OH- → BaSO4 + 2NH3 + 2H2O.
(7) Fe2+ + SO42- + Ba2+ + 2OH- → Fe(OH)2 + BaSO4.
C
A