It is difficult to determine the exact purity of a sample based solely on its melting point range. However, we can infer that the sample is impure because the observed melting point range 136.5-138.5C is lower than the literature melting point range of pure aspirin 138-140C .Impurities in a sample typically cause the melting point to decrease and the melting point range to broaden. To determine the exact purity of the sample, other analytical techniques, such as high-performance liquid chromatography HPLC or mass spectrometry, would be required.