The concept of purity in a substance refers to the absence of any contaminants or adulterants. Two common criteria for assessing the purity of a substance are:
1. **Consistency in physical properties:** A pure substance has consistent and well-defined physical properties such as melting point, boiling point, and density. These properties are characteristic of the substance and remain the same throughout the sample. For example, a chemically pure sample of water boils at 100 degrees Celsius at sea level; any deviation from this temperature could indicate the presence of impurities.
2. **Uniform chemical composition:** A pure substance contains only one type of molecule or atom, meaning it has a uniform chemical composition throughout its entirety. Chemical analysis, such as spectroscopy, chromatography, or mass spectrometry, can be used to examine the composition of a sample. In a pure compound, only a single chemical species is present, which is reflected in a clean and unambiguous spectroscopic or chromatographic signal.
Other techniques, such as X-ray diffraction for crystalline solids or various types of purity tests for pharmaceuticals, can also be used to assess purity depending on the context and the substance being examined.
State two criteria for purity
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