I pour vinegar into a glass and put inside an uncooked egg. After 24 hours I take out this egg. We can see, that this egg hasn't got a shell now and is soft. It is bouncing now.
A calcium is in the egg’s shell. (there is a calcium carbonate, witch makes, that the shell is hard and brittle at the same time). Under the influence of vinegar formed compound and calcium is washed. So vinegar reacts with the calcium- vinegar dissolves calcium. On the egg remains only a membrane, witch the vinegar doesn’t dissolve.