20.D

21.C

22.B

23.B

24.B

25.C

a, \(p+e+n=\dfrac{34.100}{68}=50\left(hạt\right)\)

PT ion: H⁺ + OH^- → H₂O

Ta có: \(\left\{{}\begin{matrix}n_{H^+}=0,05.0,5=0,025\left(mol\right)\\n_{OH^-}=0,05.0,52=0,026\left(mol\right)\end{matrix}\right.\Rightarrow OH^-dư0,001mol\)

 \(\Rightarrow\left[OH^-\right]=\dfrac{0,001}{0,1}=0,01M\)

  \(\Rightarrow pH=14+log\left(0,01\right)=12\)

Ta có: \(\left\{{}\begin{matrix}n-p=1\\n=10\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=9\\n=10\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}p=z=9\\n=10\end{matrix}\right.\)

    \(\Rightarrow A=z+n=9+10=19\left(u\right)\)

\(KHNT:^{19}_9F\)

Ta có: \(R_{tđ}=R_1+R_2+R_3=15+25+20=60\left(\Omega\right)\)

Vì I tỉ lệ ngịch với R nên I giảm 1 nửa thì R gấp đôi

 \(\Rightarrow R'_{tđ}=60.2=120\left(\Omega\right)\)

  \(\Rightarrow R_4=R'_{tđ}-R_{tđ}=120-60=60\left(\Omega\right)\)

    ⇒ Chọn D

a, \(n_{Al}=\dfrac{2,7}{27}=0,1\left(mol\right)\)

 \(m_{HCl}=109,5.10\%=10,95\left(g\right)\Rightarrow n_{HCl}=\dfrac{10,95}{36,5}=0,3\left(mol\right)\)

PTHH: 2Al + 6HCl → 2AlCl₃ + 3H₂

Mol:      0,1      0,3         0,1       0,15

Ta có: \(\dfrac{0,1}{2}=\dfrac{0,3}{6}\) ⇒ Al hết, HCl hết

\(V_{H_2}=0,15.22,4=3,36\left(l\right)\)

b, \(m_{AlCl_3}=0,1.133,5=13,35\left(g\right)\)

c, m_{dd sau pứ} = 2,7 + 109,5 - 0,15.2 = 111,9 (g)

\(C\%_{ddAlCl_3}=\dfrac{13,35.100\%}{111,9}=11,93\%\)

\(8^5.16^2.32^4=2^{15}.2^8.2^{20}=2^{43}\)

\(27^5.81^9=3^{15}.3^{36}=3^{51}\)

\(64^3.256^2=2^{18}.2^{16}=2^{34}\)

\(125^3.75^2.105^4=5^9.3^2.5^4.3^4.5^4.7^4=3^6.5^{17}.7^4\)

quá chuẩn