\(n_{Na}=\dfrac{6,9}{23}=0,3\left(mol\right)\\ 2Na+2H_2O\rightarrow2NaOH+H_2\\ n_{H_2}=\dfrac{0,3}{2}=0,15\left(mol\right)\\ a,V_{H_2\left(đktc\right)}=0,15.22,4=3,36\left(l\right)\\ b,m_{ddsaup.ứ}=m_{Na}+m_{H_2O}-m_{H_2}=6,9+100-0,15.2=106,6\left(g\right)\)

Ta có: \(n_{HCl}=\dfrac{200}{1000}.2=0,4\left(mol\right)\)

\(PTHH:Mg+2HCl--->MgCl_2+H_2\uparrow\left(1\right)\)

a. Theo PT₍₁₎: \(n_{Mg}=n_{H_2}=n_{MgCl_2}=\dfrac{1}{2}.n_{HCl}=\dfrac{1}{2}.0,4=0,2\left(mol\right)\)

\(\Rightarrow\left\{{}\begin{matrix}m_{Mg}=0,2.24=4,8\left(g\right)\\V_{H_2}=0,2.22,4=4,48\left(lít\right)\end{matrix}\right.\)

b. \(PTHH:2NaOH+MgCl_2--->Mg\left(OH\right)_2\downarrow+2NaCl\left(2\right)\)

Ta có: \(n_{NaOH}=\dfrac{\dfrac{20\%.100}{100\%}}{40}=0,5\left(mol\right)\)

Ta thấy: \(\dfrac{0,5}{2}>\dfrac{0,2}{1}\)

Vậy NaOH dư.

Theo PT₍₂₎: \(n_{Mg\left(OH\right)_2}=n_{MgCl_2}=0,2\left(mol\right)\)

\(\Rightarrow m_{Mg\left(OH\right)_2}=0,2.58=11,6\left(g\right)\)

a: \(Mg+2HCl\rightarrow MgCl_2+H_2\)

200ml=0,2 lít

\(n_{HCl}=0.2\cdot22.4=4.48\left(mol\right)\)

\(\Leftrightarrow n_{H_2}=2.24\left(mol\right)\)

\(\Leftrightarrow m_{H_2}=n_{H_2}\cdot M=2.24\cdot1=2.24\left(g\right)\)

\(n_{MgCl_2}=2.24\left(mol\right)\)

\(\Leftrightarrow n_{Mg}=2.24\left(mol\right)\)

\(\Leftrightarrow m_{Mg}=2.24\cdot24=53.76\left(g\right)\)

\(n_{AlCl_3}=\dfrac{26.7}{133.5}=0.2\left(mol\right)\)

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

\(.........0.6......0.2.......0.3\)

\(V_{H_2}=0.3\cdot22.4=6.72\left(l\right)\)

\(C\%HCl=\dfrac{0.6\cdot36.5}{300}\cdot100\%=7.3\%\)

(1)

$n_{H_2} = \dfrac{11,2}{22,4} = 0,5(mol)$
\(Mg+2HCl\rightarrow MgCl_2+H_2\)

0,5           1              0,5        0,5              (mol)

Sau phản ứng : $m_{dd} = 0,5.24 + 100 - 0,5.2 = 111(gam)$

$C\%_{MgCl_2} = \dfrac{0,5.95}{111}.100\% = 42,79\%$

(2)

Trích mẫu thử

Cho dung dịch $H_2SO_4$ tới dư vào mẫu thử :

- mẫu thử tạo khí không màu là $Na_2CO_3$
$Na_2CO_3 + H_2SO_4 \to Na_2SO_4 + CO_2 + H_2O$

- mẫu thử tạo kết tủa trắng là $BaCl_2$
$BaCl_2 + H_2SO_4 \to BaSO_4 + 2HCl$
- mẫu thử không hiện tượng là $NaNO_3$

Đáp án A

Hỗn hợp rắn gồm Al, Al₂O₃, Fe với n Fe = 2 n Al 2 O 3 . Chia thành 2 phần không bằng nhau:

n_Na = 9.2/23 = 0.4 (mol) 

2Na + 2H₂O => 2NaOH + H₂

0.4.........................0.4.......0.2

V_H2 = 0.2 * 22.4 = 4.48 (l) 

m_NaOH = 0.4 * 40 = 16 (g) 

m_dd = 9.2 + 100 - 0.2 * 2 = 108.8 (g) 

C% _NaOH = 16 / 108.8 * 100% = 14.71%

PTHH: \(Na+H_2O\rightarrow NaOH+\dfrac{1}{2}H_2\uparrow\)

Ta có: \(n_{Na}=\dfrac{9,2}{23}=0,4\left(mol\right)\)

\(\Rightarrow\left\{{}\begin{matrix}n_{NaOH}=0,4\left(mol\right)\\n_{H_2}=0,2\left(mol\right)\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}m_{NaOH}=0,4\cdot40=16\left(g\right)\\V_{H_2}=0,2\cdot22,4=4,48\left(l\right)\\m_{H_2}=0,2\cdot2=0,4\left(g\right)\end{matrix}\right.\)

Mặt khác: \(m_{dd\left(saup/ứ\right)}=m_{Na}+m_{H_2O}-m_{H_2}=108,8\left(g\right)\)

\(\Rightarrow C\%_{NaOH}=\dfrac{16}{108,8}\cdot100\%\approx14,71\%\)

nNa=9,2/23=0,4(mol).

PTPƯ: 2Na (0,4)   +      2 H2O(0,4)----> 2NaOH (0,4)+    H2(0,2).

a)VH2= 0,2.22,4=4,48(lít).

mNaOH= 0,4.40=16(g).

b)mH2=0,2.2=0,4(mol).

mdd(sau pư)=mNa+mH2O-mH2=9,2+100-0,4=108,8(g)

C%ddNaOH=16/108,8.100=14,705%.