Salicylic acid acts as a painkiller and is the active ingredient in aspirin. When a person ingests a dose of aspirin, the salicylic acid enters the blood and circulates in the bloodstream. Most of the salicylic acid is metabolised by the body. Some of the salicylic acid is excreted by the kidneys into the urine. You will estimate the concentration of salicylic acid in two solutions, S1 and S2. These solutions represent samples of blood and urine taken from a person who has ingested aspirin. Note: you will not be working with real blood or real urine. You are provided with the materials shown in Table 1.1. If any solution comes into contact with your skin, wash off immediately with cold water. It is recommended that you wear suitable eye protection. The concentration of salicylic acid can be determined by using iron(III) chloride, C, which forms a purple solution when mixed with salicylic acid. The greater the concentration of salicylic acid, the more intense the purple colour formed. You will need to: - prepare different concentrations of salicylic acid - record the intensity of purple colour for each concentration - $$\(\quad\)$$ estimate the concentration of salicylic acid in S1 and S2. You will use proportional dilution to make different concentrations of salicylic acid. You will prepare $$\(10 \mathrm{~cm}^{3}\)$$ of each concentration, using $$\(\mathbf{A}\)$$ and $$\(\mathbf{W}\)$$. Table 1.2 shows how to prepare two of the concentrations you will use. Decide which other concentrations of salicylic acid you will use. A person was given an oral dose of aspirin and the concentration of salicylic acid in their urine was measured at intervals over a period of four hours. The results are shown in Table 1.3. (i) Plot a graph of the data in Table 1.3 on the grid in Fig. 1.2. Use a sharp pencil. (ii) Use your graph in Fig. 1.2 to estimate the concentration of salicylic acid in the urine at 105 minutes. Show on your graph how you obtained your answer. concentration of salicylic acid $$\(=\)$$ ........................................ $$\(\mu \mathrm{gmL}^{-1}\)$$ (iii) The highest concentration of salicylic acid in the urine is detected at 60 minutes. Using the data in Table 1.3 and your graph in Fig. 1.2, describe the change in concentration of salicylic acid between 60 minutes and 240 minutes. ....................................................................................................................................... . ....................................................................................................................................... . ................................................................................................................................. (iv) Aspirin is also taken to reduce inflammation and blood clotting. Inflammation and blood clotting involve enzyme-controlled reactions. Suggest how aspirin reduces these enzyme-controlled reactions. ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . ....................................................................................................................................... . .................................................................................................................................

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