\(CH_3\overset{-1}{C}CH_2OH+K_2\overset{+6}{Cr_2}O_7+H_2SO_4\rightarrow CH_3\overset{+1}{C}HO+\overset{+3}{Cr_2}\left(SO_4\right)_3+K_2SO_4+H_2O\)
\(C^{-1}\rightarrow C^{+1}+2e|\times3\)
\(2Cr^{+6}+6e\rightarrow2Cr^{+3}|\times1\)
\(3CH_3CH_2OH+K_2Cr_2O_7+4H_2SO_4\rightarrow3CH_3CHO+Cr_2\left(SO_4\right)_3+K_2SO_4+7H_2O\)