What happens to DNA in the presence of a chaotropic salt?

I've used 4M Guanidine Hydro Chloride (GuHCl) for Plant RNA Viroid extraction with 25mM EDTA, 0.2M Sodium Acetate (NaAc) (pH 5), 2.5% PVP 40. Could you please tell me ;
How RNA get separated from DNA when using GuHCl?
What is the purpose of adding NaAc in Nucleic Acid Extraction?