One-dimensional Na-23 magic angle spinning (1D-MAS) NMR spectra obtained at 9.4 and 14.1 T from Na2HfO3 reveal three distinct sodium sites with widely differing NMR interaction parameters which can be accurately and unambiguously extracted. On exposure to atmospheric H2O and CO2 minor (similar to 5%) impurities can be detected by 1D-MAS. Complete resolution of the different sites is possible by use of the recently introduced two-dimensional multiple quantum technique which is used for the first time here to detect minority phases. The reaction mechanism is further elucidated by obtaining an alternative perspective from O-17 MAS Nh IR which reveals an amorphous HfO2-related phase is also formed during the decomposition process.