Final answer:
Impurities tend to lower the melting point and widen the melting point range of substances because they disrupt the crystal lattice, making it easier to melt. In manufacturing, this property is exploited to reduce production costs. In electronics, specific impurities are added to produce semiconductors with desired features.
Step-by-step explanation:
Effects of Impurities on Melting Point
Impurities typically have a significant impact on the melting point of substances. The insertion of impurities into a solid generally lowers the melting point as compared to the pure substance's melting point. This is because impurities disrupt the regular crystal lattice making it easier for the structure to break down and, therefore, melt at a lower temperature. In addition to lowering the melting point, impurities also widen the melting point range. A pure substance has a sharp melting point because all molecules shift from solid to liquid at the same temperature. However, impurities cause different parts of a substance to melt at slightly different temperatures, leading to a broader range of melting temperatures.
For instance, the addition of Al2O3 to cryolite Na3AlF6 reduces the melting point significantly, facilitating the industrial production of aluminum. Similarly, certain types of glass that blend multiple oxides have lowered melting points, making them easier and cheaper to produce. A contrasting example is found in the electronics industry, where high-purity silicon crystals are required for semiconductor applications. Here, specific impurities (dopants) are carefully introduced to impart desired electrical properties, showing that in some cases impurities can have a controlled and beneficial effect.