How membrane maintained impermeability to potassium

At 1 AM, an impermeable membrane divides a 1 liter solution of 1M NaCl in the left compartment from a 1 liter solution having both 1M NaCl and 1M KCl in the right compartment.  At 2 AM, the membrane became permeable to chloride ions.  At 4 AM, the membrane once again becomes impermeable to chloride ions.  At 6 AM, the membrane became permeable to sodium ions and, in addition, maintained chloride ion impermeability.  At 8 AM, the membrane once again became impermeable to sodium ions.  At 10 AM the membrane again became permeable to chloride ions and, in addition, maintained sodium ion impermeability.  The membrane maintained impermeability to potassium ions during the whole period.