Nickel electroplating is carried out at a current density of 2.0 A/dm² for 30 minutes. Assuming 100% current efficiency, which value is closest to the thickness of the deposit? Take Ni²⁺ + 2e⁻ → Ni, a molar mass of Ni of 58.69 g/mol, a density of 8.90 g/cm³ and a Faraday constant of 96485 C/mol.

Answer: A. About 12 µm

2.0 A/dm² is 0.020 A/cm², so the charge passed per cm² in 30 minutes (1800 s) is 0.020 × 1800 = 36 C. The deposited mass is 36 × 58.69/(2 × 96485) ≈ 1.09×10⁻² g/cm², and dividing by the density gives a thickness of 1.09×10⁻²/8.90 ≈ 1.23×10⁻³ cm, about 12 µm (12.3 µm). About 25 µm calculates the two-electron reaction with n = 1. About 1.2 mm mistakes dm² for cm² and calculates with 2.0 A/cm², making it 100 times too large (1 dm² = 100 cm²). In practice, hydrogen evolution and other side reactions bring the current efficiency below 100%, so this value is an upper-bound estimate.