Question

Calculate the number of ions, number of oxygen atom and total charge in 3gm $CO_{3}^{2-}$

Answer 1

Mass of one mole carbonate ion ($CO_{3}^{2-}$) is 12 + 16 * 3 g = 12 + 48 g = 60 g.

So, number of moles of given sample = mass given/mass of one mole

= 3gm/60gm = 1/20 moles or 0.05 moles.

Now, one mole particles are $6.022 * 10^{23}$ particles.

So, 0.05 moles of carbonate ions are $0.05 * 6.022 * 10^{23}$ particles, equaling $0.3011 * 10^{23}$, or, $3.011 * 10^{22}$ particles (ions).

There are three oxygen atoms in each carbonate ion, so total number of oxygen atoms is: $3 * 3.011 * 10^22 = 9.033 * 10^{23}$ particles.

Finally, the charge on one carbonate ion is $-2e = -2 * 1.6 * 10^{-19} C$.

So, the total charge in the sample is: $-2 * 1.6 * 10^{-19} * 3.011 * 10^{22} C$, which is equal to: $-9.613 * 10^3 C$, or, $-961.3 C$.