`a)PTHH:`
`C_2 H_5 OH+K->C_2 H_5 OK+1/2H_2 \uparrow`
`K+H_2 O->KOH+1/2H_2 \uparrow`
`b)n_[H_2]=[7,84]/[22,4]=0,35(mol)`
Gọi `n_[C_2 H_5 OH]=x;n_[H_2 O]=y`
`=>` $\begin{cases} 46x+18y=21\\\dfrac{1}{2}x+\dfrac{1}{2}y=0,35 \end{cases}$
`<=>` $\begin{cases} x=0,3\\y=0,4 \end{cases}$
`@m_[C_2 H_5 OH]=0,3.46=13,8(g)`
`@m_[H_2 O]=21-13,8=7,2(g)`