\(n_{Mg}=\dfrac{10,8}{24}=0,45\left(mol\right)\)

PTHH: Mg + H₂SO₄ --> MgSO₄ + H₂

         0,45-->0,45------>0,45--->0,45

=> \(m_{H_2SO_4}=0,45.98=44,1\left(g\right)\)

=> \(m_{ddH_2SO_4}=\dfrac{44,1.100}{20}=220,5\left(g\right)\)

m_{dd (20^oC)} = 10,8 + 220,5 - 0,45.2 - 14,76 = 215,64 (g)

\(m_{MgSO_4\left(dd.ở.20^oC\right)}=\dfrac{215,64.21,703}{100}=46,8\left(g\right)\)

=> n_{MgSO4 (tách ra)} = \(0,45-\dfrac{46,8}{120}=0,06\left(mol\right)\)

=> n_{H2O (tách ra)} = \(\dfrac{14,76-0,06.120}{18}=0,42\left(mol\right)\)

Xét n_{MgSO4 (tách ra)} : n_{H2O (tách ra)} = 0,06 : 0,42 = 1 : 7

=> CTHH: MgSO₄.7H₂O

a) 2M + 2nHCl --> 2MCln + nH2 (1)

nM=\(\dfrac{16,8}{M_M}\)(mol)

nH2=0,3(mol)

theo (1) : nM=\(\dfrac{2}{n}\)nH2=\(\dfrac{0,6}{n}\)(mol)

=>\(\dfrac{16,8}{M_M}=\dfrac{0,6}{n}=>M_M=28n\)(g/mol)

Xét thì chỉ có n=2 là phù hợp => M_M=56(g/mol)

=>M:Fe

b) Fe+ H2SO4 --> FeSO4 + H2(2)

nFe=0,45(mol)

Theo (2) : nH2SO4=nFeSO4=nH2=0,45(mol)

=> mdd_H2SO4=\(\dfrac{0,45.98.100}{10}=441\left(g\right)\)

=> mFeSO4=68,4(g)

=> mdd sau pư= 25,2+441 - 0,45.2=465,3(g)

=> C%dd_FeSO4= \(\dfrac{68,4}{465,3}.100=14,7\left(\%\right)\)

Gỉa sử muối sunfat kết tinh ngậm nước là FeSO4.nH2O

mdd sau pư còn lại sau khi muối kết tinh ngậm nước tách ra là :

465,3 - 55,6=409,7(g)

=> mFeSO4(còn lại )=\(\dfrac{409,7.9,275}{100}\approx38\left(g\right)\)

=> nFeSO4(còn lại) = 0,25(mol)

=> nFeSO4.nH2O=nFeSO4(còn lại)=0,25(mol)

=> 0,25.(152+18n)=55,6=> n\(\approx\)4

=> CT muối kết tinh là : FeSO4.4H2O

1)

\(n_{Al}=\dfrac{2,7}{27}=0,1\left(mol\right)\)

PTHH: 2Al + 3H₂SO₄ --> Al₂(SO₄)₃ + 3H₂

____0,1----->0,15

=> m_H2SO4 = 0,15.98 = 14,7(g)

=> \(C\%=\dfrac{14,7}{250}.100\%=5,88\%\)

2)

\(n_{Na_2CO_3}=\dfrac{21,2}{106}=0,2\left(mol\right)\)

PTHH: Na₂CO₃ + 2HCl --> 2NaCl + CO₂ + H₂O

_______0,2------------------------------>0,2

=> V_CO2 = 0,2.22,4 = 4,48(l)

3)

\(n_A=\dfrac{18,4}{M_A}\left(mol\right)\)

PTHH: 2A + Cl₂ --t^o--> 2ACl

____\(\dfrac{18,4}{M_A}\)---------->\(\dfrac{18,4}{M_A}\)

=> \(\dfrac{18,4}{M_A}\left(M_A+35,5\right)=46,8=>M_A=23\left(Na\right)\)

4)

n_HCl = 0,2.3 = 0,6(mol)

PTHH: M + 2HCl --> MCl₂ + H₂

____0,3<-----0,6

=> \(M_M=\dfrac{7,2}{0,3}=24\left(Mg\right)\)

\(n_{Fe}=\dfrac{16,8}{56}=0,3\left(mol\right)\\ Fe+H_2SO_4\rightarrow FeSO_4+H_2\\ 0,3.........0,3.........0,3.......0,3\left(mol\right)\\ m_{ddsau}=16,8+100=116,8\left(g\right)\\ m_{FeSO_4}=152.0,3=45,6\left(g\right)\\ C\%_{ddFeSO_4}=\dfrac{45,6}{116,8}.100\approx39,041\%\)

a) PTHH: \(SO_3+H_2O\rightarrow H_2SO_4\)

Ta có: \(n_{SO_3}=\dfrac{24}{80}=0,3\left(mol\right)=n_{H_2SO_4}\) \(\Rightarrow m_{ddH_2SO_4}=\dfrac{0,3\cdot98}{20\%}=147\left(g\right)\)

\(\Rightarrow V_{ddH_2SO_4}=\dfrac{147}{1,14}\approx128,95\left(ml\right)\)

b) PTHH: \(Fe+H_2SO_4\rightarrow FeSO_4+H_2\uparrow\)

Theo PTHH: \(n_{Fe}=n_{H_2SO_4}=n_{H_2}=0,3\left(mol\right)=n_{FeSO_4}\)

\(\Rightarrow\left\{{}\begin{matrix}m_{Fe}=0,3\cdot56=16,8\left(g\right)\\V_{H_2}=0,3\cdot24,76=7,428\left(l\right)\\m_{FeSO_4}=0,3\cdot152=45,6\left(g\right)\\m_{H_2}=0,3\cdot2=0,6\left(g\right)\end{matrix}\right.\)

Mặt khác: \(m_{dd}=m_{Fe}+m_{ddH_2SO_4}-m_{H_2}=163,2\left(g\right)\)

\(\Rightarrow C\%_{FeSO_4}=\dfrac{45,6}{163,2}\cdot100\%\approx27,94\%\)