Excess electrons are placed on a small lead sphere with a mass of 8.30 g so that its net charge is −3.70×10−9 c .
(a) find the number of excess electrons on the sphere.(b) how many excess electrons are there per lead atom? the atomic number of lead is 82, and its atomic mass is 207 g/mol?

(a)

(b)

Explanation:

(a) Let the number of the excess electrons on sphere is x.

The charge of the electron (e) = .

Given, the net charge (q) =  

Number of excess electrons is:

(b) Given that the mass of the sphere = 8.30 g

Molar mass = 207 g/mol

Since, 1 mole of Pb contains 6.022×10²³ atoms of Pb

Also, 1 mole mass = 207 g

207 g of Pb contains 6.022×10²³ atoms of Pb

1 g of Pb contains 6.022×10²³ / 207 atoms of Pb

So,

8.30 g of Pb contains (6.022×10²³ / 207)*8.30 atoms of Pb

No of atoms of Pb in 8.30g = 2.4146×10²² atoms