Also, the particularly well sealed part of the plane is the fuel tanks in the wings. Assuming they’re full of kerosene (Jet fuel is similar to Kerosene), each gallon of kerosene will hold up about 1.75# of plane.
If they’re full of air (as they are when the airplane is empty) each gallon of air will hold up about 8.33# of airplane.
So—the maximum fuel capacity of an A320 is 7842 Gallons (per wikipedia), fully loaded, the fuel tanks will hold up 13,000 pounds of boyancy. This is in addition to whatever boyancy is in the bottom hold, and other airspaces throughout the craft. Empty, the tanks will hold up about 65,000# of craft. The maximum takeoff weight is 169,000#, and the typical empty weight is about 95,000# pounds, so regardless, the tanks won’t keep it afloat, even if full of air.
However, that’s a fair amount of boyancy to keep things up for a while, while the other unsealed parts of the plane take on water.