Mercury/Mercurous Sulfate Reference Electrode (Hg/Hg2SO4) is a type of reference electrode, commonly used in electrochemical measurements. For environmental reasons it has widely replaced the saturated calomel electrode. For example, it is usually the internal reference electrode in pH meters and it is often used as reference in reduction potential measurements.

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Hg2(NO3)2 + H2SO4 → Hg2SO4 + 2 HNO3

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