why filter paper is moistened with sodium sulphate?

1.why filter paper is moistened with sodium sulphate?Explain it briefly

Are you saying about the salt bridge in the chemical cell?
The salt bridge make from the filter paper which is moistened with electroyle.
The main funtion of the salt bridge is completed the circult bewteen the 2 half cell and it can balance the charge of the 2 half cell.

2.i want to ask copper(ll)ion and nitrate ion,what would be the expected migration of colour?

copper(ll)ion is a cation(+) and the nitrate ion is the anion(-).
we put these two ions in the electrical field.
in physics , different pole will attack..
so the copper (ii) ion go to the negative pole and the nitrate ion go to the positive pole
thus you can see that the negative pole has the colour change from colorless to blue and the nitrate ion in positive has no change of colour because nitrate ion has not any colour with in.

(你不要怪我寫得不是好好...help 你解答完.)