Why is the melting point of aspirin not a reliable indicator of its purity?

The melting point of aspirin is not a reliable indicator of its purity because impurities can significantly alter the melting point range. Pure substances typically have a sharp and specific melting point, while the presence of impurities can lower and broaden this range. Additionally, factors such as moisture content and the method of preparation can affect the melting behavior. Therefore, a melting point determination alone cannot definitively indicate the purity of aspirin.