What is the total negative charge, in coulombs, of all the electrons in a small 0.900 g sphere of carbon? one mole of c is 12.0 g, and each atom contains 6 protons and 6 electrons?

The first thing you have to do is find the number of mols. That's done in terms of the masses.

mol = mass of sample / molar mass

mol = 0.900 / 12.0

mol = 0.0750 mol Carbon

Next Each mol of carbon contains 6 mol of electrons.

mol electrons = 6 * mol of carbon

mol electrons = 6 * 0.0750 = 0.450 mol

Next find out how many electrons are in 0.450 mol

1 mol = 6.02 * 10^23

0.450 mol = 6.02 * 10^23 * 0.45 = 2.71 * 10^23 electrons

Finally find the charge in coulombs

1 electron has a charge of 1.60 * 10 ^ - 19

2.71 * 10^23 electrons have a charge of 1.6*10^-19 * 2.71*10^23

The answer is 43360 Coulombs = 4.34 * 10^4 coulombs.

I have deliberately not used textbook formulas because each textbook has its own format.