Can you build muscle with five pound weights?
Yes. I've been using five pound weights (and even some 2.5lb ones for certain movements) and I've definitely seen my definition and mass improve. If five pounds is easy, up the weight a tiny bit to continue seeing progress.
No. And i will explain.
A 5 pound dumbell wont be enough to test the big muscle groups. For those your own bodyweight would be a lot better resistance weight than a 5 pound dumble. And i believe the big musclegroups are the one you should focus on. A 5 pound dumble can probably be used to build muscle but it should be one of the tools in your arsenal.
I was told a woman shouldn't lift to much weights. I wouldn't want to be a big muscular woman. We just want definition. And a five pund weight is perfect for that.