Boiling water BAD
I've had a vet say freezing is kindest for reptiles. When a person dies of hypothermia (cold) they feel cold at first, but then they start to feel warm and get silly/giddy so that is apparently a non-painful way to go for per the vet for 14ft python snake that needed euthanasia and per some human medical folks apparently a not too bad way to go as a human (after the initial cold part of course). <shrug> of course I can't _personally_ say on that method but if the zip lock method is not something you could do, perhaps your freezer could be a better alternative than the horror of vinegar&soda. But if you (or anyone) is going to hatch chicks the reality is you do need a plan/method b/c some chicks that hatch are simply not OK not going to make it & are suffering. I understand you are not an adult so you might well need an adult to partner w/ you as a plan in case this issue comes up. But everyone on the hatchalong, hard as it is, does need to have a plan just in case. It doesn't happen often, but it does happen. It is not something you want to try to figure out in the emotional moment of trying to make the decision to cull, you need to have the method planned in advance, then hopefully you won't even need to ever think about it again (or do it).