Brass is an alloy composed primarily of copper with zinc atoms substituted for some of the copper atoms in the lattice.
Pure copper at 25 °C has an electrical conductivity of 5.9×105Sm−1, whereas a typical sample of brass at the same temperature has a conductivity of 1.6×105Sm−1.
(a) Identify the type of alloy (substitutional or interstitial) formed when zinc atoms replace copper atoms in the lattice and justify your answer with reference to atomic radii.
(b) Using a particulate-level description, explain why the electrical conductivity of brass is lower than that of pure copper.
(c) Predict qualitatively how the conductivity of brass would change if the percent composition of zinc were increased from 20\% to 35\%, and justify your prediction.