The presence of impurities in a substance results in a lower melting point due to a process called melting point depression. Melting point depression is the reason why adding salt to frozen streets helps to melt the ice.
Melting point depression occurs due to the nature of a material's solid state. Most solids, such as ice, form as crystalline lattices of repeating ions or molecules. This lattice is held together by intermolecular forces that create a strong, stable structure. The solid must be heated to a certain temperature in order for this structure to be disrupted and for the solid to melt. However, the presence of impurities weakens the lattice, making it less stable. As a result, the compound melts at a lower temperature.
When working with organic compounds in a lab, the purity of the compound can be partially determined through the use of a precise measurement of the melting point. If the melting point is within the scientifically accepted range of the material's melting temperature, then the material is presumed to be pure. However, if the observed melting temperatures are outside of this range, then the compound is not pure.
One interesting effect of this process is that sea water freezes at a lower temperature than pure water. Pure water freezes at 32 degrees Fahrenheit. Sea water freezes at 28.4 degrees Fahrenheit.Learn More
Freezing point depression represents the variation in the freezing temperature of a pure solvent from that of the solvent in solution. In the equation ΔT=Kf m i, where i is the van’t Hoff factor, Kf represents the molal freezing point depression constant, also called the cryoscopic constant.Full Answer >
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The boiling point of dichloromethane is 103.3 degrees Fahrenheit. The compound has a molecular formula of CH2Cl2 and is an organic solvent that is widely used in organic chemistry.Full Answer >
The boiling point of regular household vinegar is around 213 degrees Fahrenheit. Vinegar that possesses a higher concentration of acetic acid will require a higher temperature to boil.Full Answer >