If you isolate mitochondria and place them in buffer with a low pH they begin to manufacture ATP. Why?

Mitochondrial production of ATP requires a concentration gradient of H⁺, with a high concentration at the inter membrane space and a low concentration in the matrix. The inner membrane is is impermeable to H⁺, but the outer membrane of the mitochondria will allow H⁺ to pass through.

Thus, placing mitochondria in a low pH buffer produces a H⁺ gradient that can generate ATP through ATP synthetase.