The optimal ratio of phenol to nitric acid for the preparation of 2,4-dinitrophenol is 1:2. This is because one molecule of phenol C6H5OH reacts with two molecules of nitric acid HNO3 to form 2,4-dinitrophenol C6H3N2O5 and water H2O as a byproduct. The balanced chemical equation for this reaction is:C6H5OH + 2 HNO3 C6H3N2O5 + 2 H2OMaintaining this stoichiometric ratio is important for maximizing the yield and purity of the final product. If there is an excess of nitric acid, it can lead to over-nitration, producing undesired byproducts such as 2,4,6-trinitrophenol picric acid . This would decrease the yield of 2,4-dinitrophenol and reduce the purity of the final product.Conversely, if there is an excess of phenol, the reaction may not go to completion, resulting in a lower yield of 2,4-dinitrophenol. Additionally, unreacted phenol could contaminate the final product, reducing its purity.To ensure the optimal yield and purity of 2,4-dinitrophenol, it is crucial to maintain the 1:2 ratio of phenol to nitric acid during the preparation process.