How much charge does an electron in 1 coulomb carry?

I think you're making a little bit mistake.It's about the charge an electron carries.Charge of an electron,e=-1.6*10^-19 coulomb.

So if there's 1 coulomb negative charge,there are (1/e)=6.242*10^18 electrons.

Hope you understand...

one electron has a charge of 1.602e-19 Coulomb, NOT 1 coulomb.

or

1 C = 6.242e18 electrons

I think you mean: "How many electrons are needed to give a total charge of -1C?"

The charge on 1 electron = -1.60x10⁻¹⁹ C

Therefore the total charge on N electrons = N x -1.60x10⁻¹⁹ C.

So if the total charge = -1C

N x -1.60x10⁻¹⁹ = -1

N = 1 /(1.60x10⁻¹⁹)

= 6.24x10¹⁸