What are the charge numbers for the cation and the anion in lead(II) sulfate?
1 Answer
Explanation:
The charge number is simply the ratio between the net charge of an ion and the elementary charge,
#color(blue)(|bar(ul(color(white)(a/a)"charge number" = "net charge"/"elementary charge"color(white)(a/a)|)))#
As you know, the elementary charge is the charge carried by a single proton. Alternatively, the elementary charge can be thought of as the absolute value of the charge carried by a single electron, which is equal to
Now, a formula unit of lead(II) sulfate,
- one lead(II) cation,
#1 xx "Pb"^(2+)# - one sulfate anion,
#1 xx "SO"_4^(2-)#
You're interested in finding the charge number of the lead(II) cation. A cation that carries a
The net charge of the lead(II) cation will thus be twice the charge carried by a single proton, i.e. the elementary charge
#"net charge Pb"^(2+) = 2 xx e = 2e#
This means that the charge number is equal to
#"charge number Pb"^(2+) = (2color(red)(cancel(color(black)(e))))/color(red)(cancel(color(black)(e))) = 2#
As you can see, the charge number is equivalent to the valence of the ion.
Similarly, the sulfate anion carries an overall
#"net charge SO"_4^(2-) = 2 xx (-e) = -2e#
The charge number of the sulfate anion will thus be
#"charge number SO"_4^(2-) = (-2color(red)(cancel(color(black)(e))))/color(red)(cancel(color(black)(e))) = -2#