Rust stains can be removed by washing a surface with a dilute solution of oxalic acid (H2C2O4). The reaction is Fe2O3(s) + H2C2O4(aq) → Fe(C2O4)3 3- (aq) + H2O(l) + H+(aq). Is this a redox reaction? What mass of rust can be removed by 500 mL of 0.15 M solution of oxalic acid?