WAEC Chemistry 2018 Theory — Question 14

Model answer

(i) The tin-coated plate corrodes faster. (ii) Tin is lower than zinc in the electrochemical series. A galvanized plate is simply coated with zinc; since zinc is highly reactive (higher up the electrochemical series), it corrodes preferentially, protecting the iron underneath. For a tin-coated plate, once the coating is scratched, corrosion of the iron underneath is inevitable and even faster, since tin is less reactive than iron and so does not sacrificially protect it.