A buried steel tank is protected by a magnesium sacrificial anode, $Mg Mg X^{2 +} + 2 e X^{-}$ . The protective current flowing from the anode to the tank is $0.0500 A$ on average. Find the mass of magnesium consumed in one year of $365$ days (in g, nearest integer). Take Mg = 24, $F = 96500 C mo l^{- 1}$ .

Numerical answer type, answer in g, tolerance 1.

Answer: 196 g

Charge in one year

Q = 0.0500 \times 365 \times 86400 = 1.577 \times 1 0^{6} C

, i.e.

1.577 \times 1 0^{6} /96500 = 16.34 mol

of electrons. Each Mg atom supplies

2

electrons, so moles of Mg

= 16.34/2 = 8.17 mol

. Mass

= 8.17 \times 24 = 196 g

. This is why sacrificial anodes have to be replaced periodically.