Đáp án D

1)

- TN1:

\(n_{AgCl}=\dfrac{35,875}{143,5}=0,25\left(mol\right)\)

PTHH: AgNO₃ + HCl --> AgCl + HNO₃

                          0,25<--0,25

TN2:

n_NaOH = 0,5.0,3 = 0,15 (mol)

PTHH: NaOH + HCl --> NaCl + H₂O

             0,15--->0,15

\(n_{HCl\left(dd.C\right)}=0,25+0,15\) = 0,4 (mol)

=> \(C_{M\left(dd.C\right)}=\dfrac{0,4}{2}=0,2M\)

2)

Có \(\left\{{}\begin{matrix}C_{M\left(A\right)}=\dfrac{0,25}{V}M\\C_{M\left(B\right)}=\dfrac{0,15}{V^,}M\end{matrix}\right.\)

n_HCl(A) = \(\dfrac{0,025}{V}\left(mol\right)\) 

PTHH: Fe + 2HCl --> FeCl₂ + H₂

                     \(\dfrac{0,025}{V}\)------>\(\dfrac{0,0125}{V}\)

n_HCl(B) = \(\dfrac{0,015}{V^,}\) (mol)

PTHH: Fe + 2HCl --> FeCl₂ + H₂

                    \(\dfrac{0,015}{V^,}\)-------->\(\dfrac{0,0075}{V^,}\)

TH1: \(\dfrac{0,0125}{V}=\dfrac{0,0075}{V^,}+0,02\) 

Mà V + V^' = 2 (l)

=> \(\left[{}\begin{matrix}V=1,5;V^,=0,5\left(KTM\right)\\V=0,5;V^,=1,5\left(TM\right)\end{matrix}\right.\)

=> \(\left\{{}\begin{matrix}C_{M\left(A\right)}=\dfrac{0,25}{0,5}=0,5M\\C_{M\left(B\right)}=\dfrac{0,15}{1,5}=0,1M\end{matrix}\right.\)

TH2: \(\dfrac{0,0125}{V}+0,02=\dfrac{0,0075}{V^,}\)

=> \(\left[{}\begin{matrix}V=\dfrac{1+\sqrt{6}}{2};V^,=\dfrac{3-\sqrt{6}}{2}\\V=\dfrac{1-\sqrt{6}}{2}\left(L\right)\end{matrix}\right.\)

=> \(\left\{{}\begin{matrix}C_{M\left(A\right)}=\dfrac{0,25}{\dfrac{1+\sqrt{6}}{2}}=\dfrac{-1+\sqrt{6}}{10}M\\C_{M\left(B\right)}=\dfrac{0,15}{\dfrac{3-\sqrt{6}}{2}}=\dfrac{3+\sqrt{6}}{10}M\end{matrix}\right.\)

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$200ml=0,2l$

$n_{NaOH}=0,2.1,5=0,3(mol)$

$H^++OH^-\to H_2O$

$\to n_{H^+}=n_{HCl}=n_{OH^-}=n_{NaOH}=0,3(mol)$

$\to V_{dd\,HCl}=\dfrac{0,3}{0,4}=0,75(l)=750(ml)$

Chọn C

Giải thích các bước giải:

pH = 9 → [H+] = 10⁻⁹(M)

[H+].[OH-]=10⁻¹⁴

→ [OH-] = 10⁻⁵(M)

→ nOH- = 10⁻⁵ . 1 = 10⁻⁵(mol)

pH=8 → [H+] = 10⁻⁸(M)

[H+].[OH-]=10⁻¹⁴

→ [OH-] = 10⁻⁶(M)

Gọi x lít là thể tích nước cần dùng

Ta có

\(\dfrac{10^{-5}}{x+1}\)= 10^-6

→x=9

Chọn câu C.9 lít

Câu 36 :

$n_{HCl} = 0,5.5 = 2,5(mol)$

$m_{dd\ HCl} = \dfrac{2,5.36,5}{36,5\%} = 250(gam)$
$V_{dd\ HCl} = \dfrac{m}{D} = \dfrac{250}{1,19} = 210(ml)$

Đáp án A

Câu 37  :

$Zn + 2HCl \to ZnCl_2 + H_2$
Theo PTHH :

$n_{H_2} = n_{Zn} = \dfrac{13}{65} = 0,2(mol)$
$V_{H_2} = 0,2.22,4 = 4,48(lít)

Đáp án C

Câu 50 :

Gọi $n_{FeSO_4.7H_2O} = a(mol)

Sau khi pha :

$m_{dd} = 278a + 372,2(gam)$
$n_{FeSO_4} = n_{FeSO_4.7H_2O} = a(mol)$

Vậy :

$C\%_{FeSO_4} = \dfrac{152a}{278a + 372,2}.100\% = 3,8\%$

$\Rightarrow a = 0,1(mol)$
$m_{FeSO_4.7H_2O} = 0,1.278 = 27,8(gam)$

Đáp án D

\(n_{Zn}=\dfrac{26}{65}=0,4\left(mol\right)\)

a) Pt : \(Zn+2HCl\rightarrow ZnCl_2+H_2|\)

            1         2               1          1

            0,4    0,8                          0,4

b) \(n_{H2}=\dfrac{0,4.1}{1}=0,4\left(mol\right)\)

\(V_{H2\left(dtkc\right)}=0,4.22,4=8,96\left(l\right)\)

c) \(NaOH+HCl\rightarrow NaCl+H_2O|\)

           1           1            1          1

         0,8         0,8

\(n_{NaOH}=\dfrac{0,8.1}{1}=0,8\left(mol\right)\)

\(V_{ddNaOH}=\dfrac{0,8}{2}=0,4\left(l\right)\)

 Chúc bạn học tốt

\(m_{NaOH\left(35\%\right)}=100.35\%=35\left(g\right)\)

\(m_{ddNaOH\left(20\%\right)}=\dfrac{35}{20}.100=175\left(g\right)\)

⇒ m_{nước thêm vào} = 175-100 = 75(g)

_{Vnước thêm vào} = 75.1 = 75 (ml)

Câu 4:

\(n_{HCl}=4.2,75=11\left(mol\right)\)

Ta có: \(V_{ddHCl\left(2M\right)}=\dfrac{n_{HCl\left(1\right)}}{2}\left(l\right);V_{ddHCl\left(3M\right)}=\dfrac{n_{HCl\left(2\right)}}{3}\left(l\right)\)

  \(\Rightarrow V_{ddHCl\left(2M\right)}+V_{ddHCl\left(3M\right)}=\dfrac{n_{HCl\left(1\right)}}{2}+\dfrac{n_{HCl\left(2\right)}}{3}\)

  \(\Leftrightarrow4=\dfrac{3n_{HCl\left(1\right)}+2n_{HCl\left(2\right)}}{6}\Leftrightarrow3n_{HCl\left(1\right)}+2n_{HCl\left(2\right)}=24\)

Ta có: \(\left\{{}\begin{matrix}n_{HCl\left(1\right)}+n_{HCl\left(2\right)}=11\\3n_{HCl\left(1\right)}+2n_{HCl\left(2\right)}=24\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}n_{HCl\left(1\right)}=2\\n_{HCl\left(2\right)}=9\end{matrix}\right.\)

  \(\Rightarrow V_{ddHCl\left(2M\right)}=\dfrac{2}{2}=1\left(l\right);V_{ddHCl\left(3M\right)}=\dfrac{9}{3}=3\left(l\right)\)

Câu 3:

\(m_{NaOH}=35.100\%=35\left(g\right)\\ m_{H_2O\left(thêm\right)}=a\left(g\right)\\ \Rightarrow\dfrac{35}{100+a}.100\%=20\%\\ \Leftrightarrow a=75\left(g\right)\\ \Rightarrow V_{H_2O\left(thêm\right)}=\dfrac{75}{1}=75\left(ml\right)\)

Câu 4:

\(Đặt:V_{ddHCl\left(pha.thêm2M\right)}=a\left(l\right)\\ V_{ddHCl\left(pha.thêm3M\right)}=b\left(l\right)\\ \Rightarrow\dfrac{2a+3b}{a+b}=2,75\left(1\right)\\ Mà:a+b=4\left(2\right)\\ Từ\left(1\right),\left(2\right)\Rightarrow\left\{{}\begin{matrix}a=1\left(l\right)\\b=3\left(l\right)\end{matrix}\right.\)

Vậy cần pha 1 lít dung dịch HCl 2M vào 3 lít dung dịch HCl 3M để thu được 4 lít dung dịch HCl 2,75M 

Chúc em học tốt!

1. B

2. B

(Câu 2 cậu nên sửa lại câu hỏi nhé: Khối lượng dung dịch NaOH 10% ...)

Câu 1.

\(n_{Fe}=\dfrac{5,6}{56}=0,1mol\)

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

0,1                                 0,1

\(V_{H_2}=0,1\cdot22,4=2,24\left(l\right)\)

Chọn B.

Câu 2.  \(n_{HCl}=0,2\cdot1=0,2mol\)  

       Để trung hòa: \(\Rightarrow n_{H^+}=n_{OH^-}=0,2\)

       \(m_{NaOH}=0,2\cdot40=8\left(g\right)\)

       \(m_{ddNaOH}=\dfrac{8}{10\%}\cdot100\%=80\left(g\right)\)

     Chọn B.