The melting point of benzoic acid is 122.4°C. The sample you obtained from your recrystallization showed a melting point range of 112-119°C. Briefly discuss what this tells you about the purity of your benzoic acid sample.
The Correct Answer and Explanation is:
The melting point of benzoic acid is 122.4°C, which represents its pure form. When a substance undergoes recrystallization, the purity can often be assessed by comparing its observed melting point with the known melting point of the pure substance. A pure substance usually melts within a narrow range, typically within 1-2°C of its known melting point.
In your case, the sample you obtained from recrystallization showed a melting point range of 112-119°C. This indicates that your benzoic acid sample is not completely pure, as it melts at a temperature lower than the known melting point of pure benzoic acid (122.4°C). The fact that the melting point range is spread out (112-119°C) suggests the presence of impurities within the sample. Impurities disrupt the regular arrangement of molecules in a crystalline structure, which in turn lowers the melting point and broadens the melting range.
Impurities in a substance typically lower the energy required for the solid to transition into the liquid phase. Therefore, the melting point of the impure benzoic acid sample is lower than that of the pure compound. The broader the melting point range, the greater the degree of impurity present.
In conclusion, while your recrystallized benzoic acid sample is relatively pure, the observed melting point range of 112-119°C indicates the presence of some impurities. To improve purity, further recrystallization or different purification techniques may be required to narrow the melting point range and bring it closer to the known value of 122.4°C for pure benzoic acid.
