Chọn A

KOH + HCl \(\rightarrow\)KCl + H₂O

n_KOH=0,2.0,5=0,1(mol)

m_HCl=200.\(\dfrac{a}{100}=2a\)

n_HCl=\(\dfrac{2a}{36,5}\)

Theo PTHH ta có:

n_KOH=n_HCl=0,1(mol)

=>\(\dfrac{2a}{36,5}=0,1\)

2a=3,65

=>a=1,825

KOH + HCl \(\rightarrow\)KCl + H₂O

n_KOH=0,2.0,5=0,1(mol)

Theo PTHH ta có:

n_KOH=n_HCl=0,1(mol)

m_HCl=36,5.0,1=3,65(g)

C% dd HCl=\(\dfrac{3,65}{200}.100\%=1,825\%\)

\(m_{ct}=\dfrac{5.200}{100}=10\left(g\right)\)

\(n_{NaOH}=\dfrac{10}{40}=0,25\left(mol\right)\)

Pt : \(NaOH+HCl\rightarrow NaCl+H_2O|\)

           1             1             1         1

        0,25          0,25        0,25

a) \(n_{HCl}=\dfrac{0,25.1}{1}=0,25\left(mol\right)\)

\(m_{HCl}=0,25.36,5=9,125\left(g\right)\)

\(m_{ddHCl}=\dfrac{9,125.100}{3,65}=250\left(g\right)\)

b) \(n_{NaCl}=\dfrac{0,25.1}{1}=0,25\left(mol\right)\)

⇒ \(m_{NaCl}=0,25.58,5=14,625\left(g\right)\)

\(m_{ddspu}=200+250=450\left(g\right)\)

\(C_{NaCl}=\dfrac{14,625.100}{450}=3,25\)⁰/₀

 Chúc bạn học tốt

a) \(n_{NaOH}=\dfrac{200.5\%}{40}=0,25\left(mol\right)\)

PTHH: NaOH + HCl → NaCl + H₂O

Mol:       0,25      0,25    0,25

\(m_{ddHCl}=\dfrac{0,25.36,5.100}{3,65}=250\left(g\right)\)

b) m_{dd sau pứ} = 200 + 250 = 450 (g)

\(C\%_{ddNaCl}=\dfrac{0,25.58,5.100\%}{450}=3,25\%\)

a) $NaOH + HCl \to NaCl + H_2O$

$n_{HCl} = n_{NaOH} = \dfrac{200.5\%}{40} = 0,25(mol)$

$\Rightarrow n_{HCl} = \dfrac{0,25.36,5}{3,65\%} = 250(gam)$

b)

$m_{dd\ sau\ pư} = 200 + 250 = 450(gam)$
$C\%_{NaCl} = \dfrac{0,25.58,5}{450}.100\% = 3,25\%$

[K+]=[Cl-]=0,25M

[KOH dư]=0,25M

b)   2KCl   +    H₂SO₄    ----------->K₂SO₄   + 2HCl

  0,05(mol)---->0,025(mol)

=>v_H2SO4=\(\frac{0,025}{1}\)=0,025(lít)

c)pH=-log(0,25)=0,602

(câu c mình không chắc chắn lắm nha bạn!!!)

câu a) làm sao vậy mn chỉ mik vs

a)

$n_{HCl} = \dfrac{200.7,3\%}{36,5} = 0,4(mol)$
$Ca(OH)_2 + 2HCl \to CaCl_2 + 2H_2O$
$n_{Ca(OH)_2} = \dfrac{1}{2}n_{HCl} = 0,2(mol)$
$\Rightarrow m_{dd\ Ca(OH)_2} = \dfrac{0,2.74}{14,8\%} = 100(gam)$

b)

Sau phản ứng : $m_{dd} = 200 + 100 = 300(gam)$
$C\%_{CaCl_2} = \dfrac{0,2.111}{300}.100\% = 7,4\%$

\(n_{HCl}=1\cdot0,2=0,2\left(mol\right)\\ PTHH:MgO+2HCl\rightarrow MgCl_2+H_2O\\ a,n_{MgO}=\dfrac{1}{2}n_{HCl}=0,1\left(mol\right)\\ \Rightarrow m=m_{MgO}=0,1\cdot40=4\left(g\right)\\ b,n_{MgCl_2}=n_{MgO}=0,1\left(mol\right)\\ \Rightarrow m_{MgCl_2}=0,1\cdot95=9,5\left(g\right)\\ c,m_{CT_{HCl}}=0,2\cdot36,5=7,3\left(g\right)\\ \Rightarrow C\%_{HCl}=\dfrac{7,3}{250}\cdot100\%=2,92\%\)

\(n_{H_2O}=n_{MgO}=0,1\left(mol\right)\\ \Rightarrow m_{H_2O}=0,1\cdot18=1,8\left(g\right)\\ \Rightarrow m_{dd_{MgCl_2}}=4+250-1,8=252,2\left(g\right)\\ \Rightarrow C\%_{MgCl_2}=\dfrac{9,5}{252,2}\cdot100\%\approx3,77\%\)

Đáp án B

Fe+2HCl → FeCl₂ + H₂

a      2a           a           a

Mg + 2HCl → MgCl₂+H₂

b         2b         b         b

m_{chất rắn X} = 56a + 24b ; m_ddHCl = 36,5/20% .2.(a + b) = 365(a + b)

⇒ m_{ddsau pư} = 56a + 24b + 365(a + b) – 2(a + b) = 419a + 387b

.100 = 15,76

Giải PT ⇒ a = b  ⇒ .100 = 11,79%