mdd=mct+mdm=46+500=546(g)
C%=46/546.100%=8.42%
2Na+2H2O\(\rightarrow\)2NaOH+H2
\(n_{Na}=\dfrac{46}{23}=2mol\)
\(n_{NaOH}=n_{Na}=2mol\rightarrow m_{NaOH}=2.40=80gam\)
\(n_{H_2}=\dfrac{1}{2}n_{Na}=\dfrac{1}{2}.2=1mol\rightarrow m_{H_2}=1.2=2gam\)
\(m_{dd}=m_{Na}+m_{H_2O}-m_{H_2}=46+500-2=544g\)
C%NaOH=\(\dfrac{80}{544}.100\%\approx14,7\%\)