Question

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Why do soluble impurities affect the melting point while insoluble impurities are expected not to affect the melting point? (3 points)

Answer 1

Thia phenomenon is known as melting point depression. Most of the pure solid are present in perfectly arreanged in crystalline solids. This have molecules or set of ions arranged in regular, repeating and closely packed in crystal lattice. The lattice are held together by various intermolecular forces of attraction during melting of such of compounds the energy provide overcome with this intermolecular forces of attraction and hence compound with absence of soluble impurities melt at high temperature. When soluble impurities are introduced this impurities disrupt the perfect arrangements of molecules in crystal lattice. This impurities disrupt repeating pattern of forces that hold the solid together. Energy required for melting of such material is lower the energy required is lesser as compared to henenery required for pure sample. For solid with soluble impurities melt at lower temperature as compared to pure sample this is known as melting point depression. Non soluble impurities does not effect or disrupt the repeating pattern of molecules in crystal lattice. Their intermolecular forces of attraction remain unaffected. Hence non soluble impurities does not affect melting of solid.