Đáp án là B. 4,48

1)

a)

$CaO + 2HCl \to CaCl_2 + H_2O$
$CaCO_3 + 2HCl \to CaCl_2 + CO_2 + H_2O$

$n_{CaCO_3} = n_{CO_2} = 0,2(mol)$
$n_{CaCl_2} = 0,3(mol)$

Suy ra: 

$n_{CaO} = 0,3 - 0,2 = 0,1(mol)$
$\%m_{CaO} = \dfrac{0,1.56}{0,1.56 + 0,2.100}.100\% = 21,875\%$

$\%m_{CaCO_3} = 78,125\%$

b) 

$m_{dd} = 0,1.56 + 0,2.100 + 50 - 0,2.44 = 66,8(gam)$
$C\%_{CaCl_2} = \dfrac{33,3}{66,8}.100\% = 49,85\%$

Câu 4 : 

a)

Gọi $n_{Fe} = a(mol) ; n_{MgO} = b(mol)$

Suy ra: $56a + 40b = 19,2(1)$

$Fe + 2HCl \to FeCl_2 + H_2$
$MgO + 2HCl \to MgCl_2 + H_2O$
Theo PTHH : $n_{HCl} = 2a + 2b = 0,4.2 = 0,8(2)$
Từ (1)(2) suy ra a = b = 0,2

$\%m_{Fe} = \dfrac{0,2.56}{19,2}.100\% = 58,33\%$
$\%m_{MgO} = 100\% -58,33\% = 41,67\%$

b)

$n_{FeCl_2} = a = 0,2(mol)$
$n_{MgCl_2} = b = 0,2(mol)$

$m_{muối} = 0,2.127 + 0,2.95 = 44,4(gam)$

Ta có: \(\left\{{}\begin{matrix}n_{CO_2}=\dfrac{4,48}{22,4}=0,2\left(mol\right)\\n_{CaCl_2}=\dfrac{33,3}{111}=0,3\left(mol\right)\end{matrix}\right.\)

PTHH: \(CaCO_3+2HCl\rightarrow CaCl_2+CO_2\uparrow+H_2O\)

                    0,2_____0,4_____0,2____0,2_____0,2  (mol)

            \(CaO+2HCl\rightarrow CaCl_2+H_2O\)

                 0,1_____0,2_____0,1____0,1    (mol)

Ta có: \(\left\{{}\begin{matrix}m_{CaO}=0,1\cdot56=5,6\left(g\right)\\m_{CaCO_3}=0,2\cdot100=20\left(g\right)\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}\%m_{CaO}=\dfrac{5,6}{5,6+20}\cdot100\%=21,875\%\\\%m_{CaCO_3}=78,125\%\end{matrix}\right.\)

Mặt khác: \(m_{CO_2}=0,2\cdot44=8,8\left(g\right)\)

\(\Rightarrow m_{dd\left(sau.p/ứ\right)}=m_{CaO}+m_{CaCO_3}+m_{ddHCl}-m_{CO_2}=66,8\left(g\right)\)

\(\Rightarrow C\%_{CaCl_2}=\dfrac{33,3}{66,8}\cdot100\%\approx49,85\%\)

nCO2=\(\dfrac{4,48}{22,4}=0,2\) mol

nCaCl₂=\(\dfrac{33,3}{111}=0,3\)

CaCO₂ + 2HCl → CaCl₂ + CO₂ + H₂O

  0,2           ←         0,2    ← 0,2

CaO + 2HCl  → CaCl₂ + H₂O     

 0,1              ←    0,1

a)  % CaO=\(\dfrac{0,1.56}{0,1.56+0,2.100}.100\%=21,875\%\)    

   % CaCO₃ =100% - 21,875%= 78,125%

b) a = mCaO+mCaCO₃ =0,1.56+0,2.100=25,6g

mdd sau pư= a + mddHCl - mCO2

                  = 25,6 + 50 - 0,2.44=66,8g

C%CaCl₂=\(\dfrac{33,3}{66,8}.100\%\simeq49,85\%\)

Chọn đáp án A

n H 2 O = n C O 2 = a m o l ⇒ n H C l = 2 n H 2 O = 2 a m o l

Bảo toàn khối lượng: 20 , 6 + 2 a . 36 , 5 = 22 , 8 + 44 a + 18 a ⇒ a = 0 , 2 m o l ⇒ V = 0 , 2 . 22 , 4 = 4 , 48 l

Đáp án D

Sơ đồ phản ứng: