page 12 27. The melting point of an impure substance was determined to be 111 °C – 114 °C. After purification, the melting point should be A higher and over a wider range B higher and over a narrower range C lower and over a wider range D lower and over a narrower range. 28. During the technique of heating to constant mass, the purpose of the desiccator is to A prevent reaction with oxygen in the air B remove water from the compound C prevent reabsorption of water D prevent decomposition. 29. Using thin-layer chromatography, the components of a sample can be identified by Rf values. Which of the following affects the Rf value for an individual component? A The distance moved by the solvent. B The concentration of the sample. C The length of TLC plate. D The solvent used.