Câu 1 : 

\(n_{KOH}=\dfrac{25\%.112}{100\%.56}=0,5\left(mol\right)\)

Pt : \(2KOH+H_2SO_4\rightarrow K_2SO_4+2H_2O\)

\(n_{H2SO4}=\dfrac{1}{2}n_{KOH}=0,25\left(mol\right)\Rightarrow m_{ddH2SO4}=\dfrac{0,25.98}{4,9\%}.100\%=500\left(g\right)\)

Ta có: \(C\%_{KOH}=\dfrac{m_{KOH}}{m_{KOH}+m_{H_2O}}.100\%\)

\(\Rightarrow\dfrac{m_{KOH}}{m_{KOH}+400}=0,12\)

\(\Rightarrow m_{KOH}=\dfrac{600}{11}\left(g\right)\)

\(n_{OH^-}=n_{KOH}=\dfrac{1,12}{56}=0,02mol\)

Để trung hòa\(\Rightarrow n_{H^+}=n_{OH^-}=0,02mol\)

\(\Rightarrow n_{H_2SO_4}=\dfrac{1}{2}n_{H^+}=0,01mol\Rightarrow m=0,98g\)

\(m_{dd}=\dfrac{0,98}{35}\cdot100=2,8\left(g\right)\)

Chọn C.

\(\text{1)}m_{KOH}=40.35\%=14\left(g\right)\\ \rightarrow n_{KOH}=\dfrac{14}{56}=0,25\left(mol\right)\\ PTHH:KOH+HCl\rightarrow KCl+H_2O\\ \text{Theo pthh}:n_{HCl}=n_{KOH}=0,25\left(mol\right)\\ \rightarrow V_{ddHCl}=0,25.0,5=0,125\left(l\right)\)

\(\text{2)}n_{Al}=\dfrac{4,05}{27}=0,15\left(mol\right)\\ n_{H_2SO_4}=200.14,7\%=29,4\left(g\right)\\ \rightarrow n_{H_2SO_4}=\dfrac{29,4}{98}=0,3\\ \text{PTHH}:2Al+3H_2SO_4\rightarrow Al_2\left(SO_4\right)_3+3H_2\uparrow\\ \text{LTL}:\dfrac{0,15}{2}< \dfrac{0,3}{3}\rightarrow H_2SO_4\text{ dư}\)

\(\text{Theo pthh}:\left\{{}\begin{matrix}n_{H_2SO_4\left(pư\right)}=\dfrac{3}{2}n_{Al}=\dfrac{3}{2}.0,15=0,225\left(mol\right)\\n_{H_2}=n_{H_2SO_4\left(pư\right)}=0,225\left(mol\right)\\n_{Al_2\left(SO_4\right)_3}=\dfrac{1}{2}n_{Al}=\dfrac{1}{2}.0,15=0,075\left(mol\right)\end{matrix}\right.\\ \rightarrow m_{dd\left(\text{sau phản ứng}\right)}=200+4,05-0,3.2=203,45\left(g\right)\)

\(\rightarrow\left\{{}\begin{matrix}C\%_{H_2SO_4\text{ dư}}=\dfrac{\left(0,3-0,225\right).98}{203,45}=3,61\%\\C\%_{Al_2\left(SO_4\right)_3}=\dfrac{342.0,075}{203,45}=12,61\%\end{matrix}\right.\)

nH2SO4=0,02.1=0,02(ol)

a) PTHH: 2 NaOH + H2SO4 -> Na2SO4 + 2 H2O

0,04____________0,02____0,02(mol)

mNaOH=0,04.40= 1,6(g)

=>mddNaOH= (1,6.100)/20= 8(g)

b) PTHH: H2SO4 + 2 KOH -> K2SO4 + 2 H2O

0,2____________0,04(mol)

=>mKOH=0,04.56=2,24(g)

=>mddKOH= (2,24.100)/5,6=40(g)

=>VddKOH= mddKOH/DddKOH= 40/1,045=38,278(ml)

Tìm thể tích dung dịch KOH

- Phương trình hoá học :

H 2 SO 4  + 2KOH →  K 2 SO 4  + 2 H 2 O

- Số mol KOH tham gia phản ứng :

n KOH = 2 n H 2 SO 4  = 0,02 x 2 = 0,04 mol

- Khối lượng KOH tham gia phản ứng : mKOH = 0,04 x 56 = 2,24 (gam).

- Khối lượng dung dịch KOH cần dùng :

m dd   KOH  = 2,24x100/5,6 = 40 gam

- Thể tích dung dịch KOH cần dùng:

V dd   KOH  = 40/1,045 ≈ 38,278 ml

\(Cu\left(OH\right)_2+2HCl->CuCl_2+H_2O\\ n_{Cu\left(OH\right)_2}=\dfrac{4,9}{98}=0,05< \dfrac{n_{HCl}}{2}=\dfrac{2.0,15}{2}=0,15\Rightarrow HCl:dư\left(0,05mol\right)\\ M\left(OH\right)_2+2HCl->MCl_2+H_2O\\ Có:0,228.25.1,3.2:\left(M+34\right)=0,05.36,5\\ M=-33\left(loại\right)\)

Vậy không có kim loại M thoả đề