Soda bottle bubbling when opened: mixing as before it was opened nothing was happening but as it came in contact with atmosphere it started to bubble.
Bright copper statue turning green from weathering: mixing as all vapors and gases in atmosphere combined with copper of that statue they started to change color of statue
Removing salt from seawater: obviously removing as one component
Water decomposing: obviously separating as it's constituent elements are removed from compound and converted into individual elements
