초록
산성용액중에서 백금음극을 사용하여 중크롬산이온의 환원을 전위주사법 및 정전위전해에 의하여 검토하였다. 지지전해질로서 황산나트륨(pH 1.5∼4.0)을 사용한 비완충용액중의 중크롬산칼륨의 분극곡선은 3단파가 생기며 첫째파 및 둘째파의 파고는 각각 크롬(Ⅵ)농도 및 수소이온의 활동도에 비례하나 셋째파는 어느 것에도 비례하지 않았다. 첫째 및 둘째 peak이 전류는 전위주사속도(${\nu}$)에 비례하나 셋째 peak는 50mV/sec이하의 늦은 주사속도에서 ${\nu}^{1/2}$에 비례하였다. 정전위전해에 의하면, 크롬(Ⅵ)의 환원은 셋째 peak보다 더 base이고 초기 pH가 약 2.3 이상이 되면 완전히 억제되었다. 그러므로 이 세 peak는 각각 $Cr_2O_7^{\to}Cr^{3+},\;2H^+{\to}H_2$ 및 음극피막의 형성으로 간주하였다.
Reduction of dichromate at a platinum cathode in acid solution was studied by cyclic voltammetry and controlled potential electrolysis. Cathodic polarization curve consisted of three waves in unbuffered solution of potassium dichromate having initial pH ranges 1.5∼4.0, with sodium sulfate as the supporting electrolyte. Relative heights of the first and the second waves were, respectively, a function of chromium (Ⅵ) concentration and activity of hydrogen ion, but that of the third wave was not proportional to both of them. The current of the first two peaks were proportional to the sweep rate of potential (${\nu}$), while that of the last peak vs. ${\nu}^{1/2}$ was linear at the sweep rate of less than 50mV/sec. By the controlled potential electrolysis, the reduction of chromium (Ⅵ) was almost completely suppressed at potentials more negative than the last peak and at initial pH's above ca. 2.3 of unbuffered solution. Therefore, these peaks represented, respectively, $Cr_2O_7^{2-}{\to}Cr^{3+},\;2H^+{\to}H_2$ and the formation of a cathodic film.