a) BaCl2 + Na2SO4 → BaSO4↓ + 2NaCl
\(V_{ddBaCl_2}=\dfrac{240}{1,2}=200\left(ml\right)=0,2\left(l\right)\)
\(\Rightarrow n_{BaCl_2}=0,2\times1=0,2\left(mol\right)\)
\(m_{Na_2SO_4}=400\times14,2\%=56,8\left(g\right)\)
\(\Rightarrow n_{Na_2SO_4}=\dfrac{56,8}{142}=0,4\left(mol\right)\)
Theo PT: \(n_{BaCl_2}=n_{Na_2SO_4}\)
Theo bài: \(n_{BaCl_2}=\dfrac{1}{2}n_{Na_2SO_4}\)
Vì \(\dfrac{1}{2}< 1\) ⇒ BaCl2 hết, Na2SO4 dư
b) Dung dịch A gồm: NaCl và Na2SO4 dư
Theo PT: \(n_{BaSO_4}=n_{BaCl_2}=0,2\left(mol\right)\)
\(\Rightarrow m_{BaSO_4}=0,2\times233=46,6\left(g\right)\)
\(\Rightarrow m_{dd}saupư=240+400-46,6=593,4\left(g\right)\)
Theo PT: \(n_{NaCl}=2n_{BaCl_2}=2\times0,2=0,4\left(mol\right)\)
\(\Rightarrow m_{NaCl}=0,4\times58,5=23,4\left(g\right)\)
\(\Rightarrow C\%_{NaCl}=\dfrac{23,4}{593,4}\times100\%=3,94\%\)
Theo PT: \(n_{Na_2SO_4}pư=n_{BaCl_2}=0,2\left(mol\right)\)
\(\Rightarrow n_{Na_2SO_4}dư=0,4-0,2=0,2\left(mol\right)\)
\(\Rightarrow m_{Na_2SO_4}dư=0,2\times142=28,4\left(g\right)\)
\(\Rightarrow C\%_{Na_2SO_4}dư=\dfrac{28,4}{593,4}\times100\%=4,79\%\)
