Bài 7:
2R+2H2O\(\rightarrow\)2ROH+H2
\(n_{H_2}=\dfrac{2,576}{22,4}=0,115mol\)
\(n_R=n_{ROH}=2n_{H_2}=2.0,115=0,23mol\)
\(M_R=\dfrac{8,97}{0,23}=39\left(Kali:K\right)\)
\(m_{KOH}=0,23.56=12,88g\)
\(m_{dd}=8,97+100-0,115.2=108,74g\)
C%KOH=\(\dfrac{12,88}{108,74}.100\approx11,84\%\)
Bài 8:
R+2H2O\(\rightarrow\)R(OH)2+H2
R(OH)2+2HCl\(\rightarrow\)RCl2+2H2O
\(n_{HCl}=0,1mol\)
\(n_R=n_{R\left(OH\right)_2}=\dfrac{1}{2}n_{HCl}=\dfrac{0,1}{2}=0,05mol\)
\(M_R=\dfrac{6,85}{0,05}=137\left(Bari:Ba\right)\)
\(m_{Ba\left(OH\right)_2}=0,05.171=8,55g\)
Bài 9:
-Gọi R là kí hiệu chung cho 2 kim loại kiềm
2R+2H2O\(\rightarrow\)2ROH+H2
ROH+HCl\(\rightarrow\)RCl+H2O
\(n_{H_2}=\dfrac{0,336}{22,4}=0,015mol\)
\(n_{RCl}=n_{ROH}=2n_{H_2}=2.0,015=0,03mol\)
\(M_{RCl}=\dfrac{2,075}{0,03}\approx69,2\)
\(\rightarrow R+35,5=69,2\rightarrow R=33,7\)
Na=23<R=33,7<K=39
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