2Na + 2H2O → 2NaOH + H2
\(n_{Na}=\dfrac{6,9}{23}=0,3\left(mol\right)\)
Theo PT: \(n_{NaOH}=n_{Na}=0,3\left(mol\right)\)
\(\Rightarrow m_{NaOH}=0,3\times40=12\left(g\right)\)
Theo PT: \(n_{H_2}=\dfrac{1}{2}n_{Na}=\dfrac{1}{2}\times0,3=0,15\left(mol\right)\)
\(\Rightarrow m_{H_2}=0,15\times2=0,3\left(g\right)\)
\(m_{ddNaOH}=m_{Na}+m_{H_2O}-m_{H_2}=6,9+224-0,3=230,6\left(g\right)\)
\(\Rightarrow C\%_{ddNaOH}=\dfrac{12}{230,6}\times100\%=5,204\%\)
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