Gọi số mol clo đã phản ứng là x (mol)
PTHH : Cl2 + 2KBr \(\rightarrow\) 2KCl + Br2
x 2x 2x x (mol)
\(\Rightarrow m_{KBr_{dư}}=3,125-2x.\left(80+39\right)=3,125-238x\left(g\right)\)
mrắn khan = \(m_{KBr_{dư}}\)+ mKCl
\(\Leftrightarrow2,0125=3,125-238x+2x.74,5\)\(\Leftrightarrow\) x = 0,0125 (mol)
\(\Rightarrow m_{Cl_2}=0,0125.71=0,8875\left(g\right)\)
\(C\%_{Cl_2}=\dfrac{0,8875}{31,25}.100\%=2,84\%\)