A chamber for use in a submersible pump assembly. The submersible pump assembly has a submersible motor which is connected to a power source and which will drive a submersible pump in the submersible pump assembly. A motor protector with expansion chamber is connected to the submersible motor. The expansion chamber and submersible motor are filled with motor oil. The expansion chamber has a housing and a reactant disposed in the housing interior for reacting with and reducing the concentration of contaminants present in the well fluid that are harmful to components of the motor protector.