alright well i made a seal around my cup and i got it to work but the balloon didn't fill up all the way because its one of those long balloons where its hard for human lungs to even inflate, and the seal kept breaking so that tells me that the balloon is harder to inflate then it is to break a play dough seal lol.
so i'm gonna try getting a bigger round balloon and see if that helps. also i am going to use your idea muz with the lime water i just have to tell my teacher to get me some calcium hydroxide. thanks guys