Subject: Why don't protons diffuse out of the mitochondrion during chemiosmosis?

I am teaching cellular respiration and we teach that the external membrane of
the mitochondrion is permeable to ions and molecules up to a specific size. I
was asked by a student why protons do not diffuse from the inter membrane space
of the mitochondrion into the cytosol instead of diffusing back into the matrix.
 Does it have to do with the pH in the matrix being higher than the pH in the
cytosol, creating a greater proton gradient?

Re: Why don't protons diffuse out of the mitochondrion during chemiosmosis?