What mass of platinum could be plated on an electrode from the electrolysis of a Pt(NO3)2 solution?

Question

with a current of 0.500 A for 55.0 s?

Answer 1

This is 27.5 coulombs, which gives 27.5/(2 x 96500) moles.  Multiplying by the atomic weight (195) gives 27.8 milligrams.

The magic number 96,500 comes from multiplying Avogadro's number (6E23) by the charge on an electron (1.6E-19).