A copper sphere of mass 2.0 g contains about 2 x 1022 atoms. The charge on the nucleus of each atom is 29 e (e = electronic charge). The mass of an electron is 9.11 x 10-31kg.How much mass will the sphere lose or gain if it is given a charge of +2 μC?

To give positive charge to the copper sphere, a certain number of free electrons must be removed.The total number of electrons is 29×2×1022=5.8×1023Since a positive charge of 2 μC is to be given the number of electrons to be removed =2×10−61.6×10−19=1.25×1013The mass of the electrons removed=1.25×1013×0.91×10−30kg=1.13×10−17kg=1.13×10−14gThis mass will be lost by the copper sphere.