You conduct an experiment where you use a single battery with a charge capacity

Question

You conduct an experiment where you use a single battery with a charge capacity of900 mAh to precipitate an unknown metal from a salt solution that was leaking from an old battery. You use a vast excess of the salt, so the amount of metal condensed is limited by the battery. You obtain 3.368 g of the metal. You can assume that the metal was the only substance being reduced in the electrochemical cell and 100% of the listed battery charge is useable. If you were able to determine that the metal ion was a +2 ion, then which metal is it? This metal was used in batteries for a long time (even in "alkaline" batteries) due to its good electrochemical properties, but it is now being phased out. Why? (Show your work for full credit)

Explanation / Answer

Charge capacity of battery = 900 mAh

Mass of metal deposited = 3.368 g

Charge on metal ion = +2

Using Faraday's law of electrolysis -

m = (It/F)(M/z)

3.368 = (0.90 * 3600 / 96485)(M/2)

M = 200.59 g/mol

Molecular mass 200.59 g/mol corresponds to Mercury, Hg.

Mercury batteries are phased out now due to the content of toxic mercury and environmental concerns about its disposal.

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