2. Ta có: m_{KOH 20%} = \(\frac{200.20}{100}\) ₌ 40g

m_{KOH 10%} = m_KOH 20% = 40g

=>m_{dd KOH 10%}  = \(\frac{40.100}{10}\) = 400g

=> m_H2O = 400 - 200 =200g

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

            \(Na_2O+H_2O\rightarrow2NaOH\)

Ta có: \(\left\{{}\begin{matrix}n_{NaOH}=n_{Na}+2n_{Na_2O}=\dfrac{4,6}{23}+2\cdot\dfrac{6,2}{62}=0,3\left(mol\right)\\n_{H_2}=\dfrac{1}{2}n_{Na}=0,05\left(mol\right)\end{matrix}\right.\) \(\Rightarrow\left\{{}\begin{matrix}m_{NaOH}=0,3\cdot40=12\left(g\right)\\m_{H_2}=0,05\cdot2=0,1\left(g\right)\end{matrix}\right.\)

Mặt khác: \(m_{dd\left(sau.p/ứ\right)}=m_{Na}+m_{Na_2O}+m_{H_2O}-m_{H_2}=110,7\left(g\right)\)

\(\Rightarrow C\%_{NaOH}=\dfrac{12}{110,7}\cdot100\%\approx10,84\%\)

Theo gt ta có: $n_{Na}=0,2(mol);n_{Na_2O}=0,1(mol)$

$2Na+2H_2O\rightarrow 2NaOH+H_2$

$Na_2O+H_2O\rightarrow 2NaOH$

Ta có: $n_{NaOH}=0,4(mol);n_{H_2}=0,1(mol)$

Bảo toàn khối lượng ta có: $m_{dd}=110,6(g)$

$\Rightarrow \%C_{NaOH}=14,46\%$

\(n_{Na}=\dfrac{m}{M}=0,2mol\)

\(n_{Na2O}=\dfrac{m}{M}=0,1\left(mol\right)\)

\(BTNT\left(Na\right):n_{NaOH}=0,2+2.0,1=0,4\left(mol\right)\)

\(\Rightarrow m_{NaOH}=n.M=16g\)

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

...............0,2...................................0,1.

\(\Rightarrow m_{dd}=m_{KL}+m_{H2O}-m_{H2}=110,6g\)

\(\Rightarrow C\%_{NaOH}=\dfrac{m}{m_{dd}}.100\%=14,46\%\)

Câu 1 :

mNaCl = 5.85*100/100= 5.85 g

mH2SO4 = 100*49/100=49 g

mNaOH = 100*20/100=20 g

BaSO4 không tan trong nước nên không tính được

Câu 2 :

nNa = 2.3/23 = 0.1 mol

Na + H2O --> NaOH + 1/2H2

0.1___________0.1______0.05

mdd sau phản ứng = 2.3 + 100 - 0.1 = 102.2 g

mNaOH = 4g

C%NaOH = 4/102.2*100% = 3.91%

Câu 3 :

nCa = 0.05 mol

Ca + 2H2O --> Ca(OH)2 + 2H2

0.05____________0.05_____0.1

mdd = 100 + 2 - 0.2 = 101.8 g

mCa(OH)2 = 3.7 g

C%Ca(OH)2 = 3.63%

Câu 4 :

nH2 = 5*10^-5 mol

Ca + 2H2O --> Ca(OH)2 + H2

5*10^-5__________5*10^-5__5*10^-5

mCa = 0.002 g

mCa(OH)2 = 0.0037 g

mdd sau phản ứng = 100 g

C%Ca(OH)2 = 0.0037%

1)
Na2O + H2O --> 2NaOH
0.1 0.2 (mol)
C% =(0,2. 40)/(100 + 6,2) = 7,53%

Câu 1:

\(n_{Na_2O}=\dfrac{6,2}{62}=0,1mol\)

Na₂O+H₂O\(\rightarrow\)2NaOH

\(n_{NaOH}=2n_{Na_2O}=0,2mol\)

\(C\%_{NaOH}=\dfrac{0,2.40.100}{100+6,2}\approx7,53\%\)

Câu 2:

\(n_{Na}=\dfrac{6,2}{23}mol\)

2Na+2H₂O\(\rightarrow\)2NaOH+H₂

Số mol NaOH=số mol Na=\(\dfrac{6,2}{23}mol\)

Số mol H₂=0,5 số mol Na=\(\dfrac{3,1}{23}mol\)

m_dd=6,2+100-\(\dfrac{3,1}{23}.2\approx105,93g\)

\(C\%_{NaOH}=\dfrac{\dfrac{6,2}{23}.40.100}{105,93}\approx10,2\%\)

a) $Mg + 2HCl \to MgCl_2 + H_2$
$n_{MgCl_2} = \dfrac{4,75}{95} = 0,05(mol)$

$n_{HCl} = 2n_{MgCl_2} = 0,1(mol)$
$m_{dd\ HCl} = \dfrac{0,1.36,5}{14,6\%} = 25(gam)$
$\Rightarrow V_{dd\ HCl} = \dfrac{25}{1,12} = 22,32(ml)$

b) $n_{Mg} = n_{H_2} = n_{MgCl_2} = 0,05(mol)$
$\Rightarrow m_{dd\ sau\ pư} = 0,05.24 + 25 - 0,05.2  = 26,1(gam)$

$C\%_{HCl} = \dfrac{4,75}{26,1}.100\% = 18,2\%$

Bài 7 : Theo đề bài ta có : \(\left\{{}\begin{matrix}nNa=\dfrac{m1}{23}mol\\nNa2O=\dfrac{m2}{62}mol\end{matrix}\right.\)

Ta có PTHH 1 :

2Na + 2H2O \(\rightarrow\) 2NaOH + H2

\(\dfrac{m1}{23}mol..........\dfrac{m1}{23}mol..\dfrac{1}{2}.\dfrac{m1}{23}mol\) = \(\dfrac{m1}{46}mol\)

=> mddNaOH = m1 + p - 2.\(\dfrac{m1}{46}=m1+p-\dfrac{m1}{23}\)

mct = mNaOH = 40.\(\dfrac{m1}{23}\) = \(\dfrac{40.m1}{23}\left(g\right)\)

=> a% = \(\dfrac{\dfrac{40m1}{23}}{m1+p-\dfrac{m1}{23}}.100\%=\dfrac{4000m1}{22m1+23p}\%\left(1\right)\)

Ta có PTHH 2 :

Na2O + H2O \(\rightarrow\) 2NaOH

\(\dfrac{m2}{62}mol.........2\dfrac{m2}{62}=\dfrac{m2}{31}mol\)

=> mddNaOH = \(m2+p\) (g)

mct = mNaOH = \(40.\dfrac{m2}{31}=\dfrac{40.m2}{31}\left(g\right)\)

=> a% = \(\dfrac{\dfrac{40m2}{31}}{m2+p}.100\%=\dfrac{4000m2}{31m2+31.p}\) % (2)

Ta có (1) = (2)

<=> \(\dfrac{4000m1}{22m1+23p}\) = \(\dfrac{4000m2}{31m2+31p}\)

<=> 4000m2 ( 22m1 + 23p ) = 4000m1( 31m2 + 31p )

Phần rút gọn dễ nên bạn tự rút gọn nha !

`n_{Na_2O}={4,6}/{62}\approx 0,074(mol)`

`Na_2O+H_2O->2NaOH`

`0,074->0,074->0,148(mol)`

`a)\ C_{M\ NaOH}={0,148}/{0,2}=0,74M`

`b)\ C\%_{NaOH}={0,148.40}/{200.1,12}.100\%\approx 2,64\%`