When you use UV Vis to determine the purity of the product- how does knowing the amount of salicylic acid help? Do you only use this when you know (after adding Fe3+) that the aspirin isn't pure? I know there is a very simple answer to this question...
When using UV Vis spectroscopy to determine the purity of a product, knowing the amount of salicylic acid can be helpful in a couple of ways.
Firstly, UV Vis spectroscopy measures the absorption of light by a sample at specific wavelengths. Each compound has a characteristic absorption spectrum, which can be used to identify and quantify its presence in a mixture. In the case of salicylic acid and aspirin, both compounds have different absorption spectra, allowing us to differentiate between them. By comparing the absorption of light by the sample at the known wavelength for salicylic acid, we can determine the amount of salicylic acid present in the mixture.
Secondly, the knowledge of the amount of salicylic acid is useful when the aspirin sample is impure. If the sample contains other impurities or byproducts, these can also contribute to the absorption of light at specific wavelengths. By subtracting the absorption due to salicylic acid (which is known) from the total absorption of the sample, we can obtain the absorption contributed by the impurities. This allows us to estimate the purity of the aspirin product.
In summary, knowing the amount of salicylic acid helps in determining the purity of the aspirin product using UV Vis spectroscopy. It allows us to differentiate between salicylic acid and aspirin based on their unique absorption spectra and helps in quantifying the amount of salicylic acid present in the sample. Additionally, it assists in estimating the purity of the product by subtracting the absorption due to salicylic acid from the total absorption of the impure sample.