Is it possible for the ph of a stored solution to change over time?
Like say if i were to make a solution of distilled water & 5% distilled white vinegar with a ph of 4 & store it in a mason jar with the lid on in the fridge for a week or 2 while the other materials for the extraction were slowly acquired would the ph change over time or is ph pretty stable?

Its going to be stable, if sealed.