calculate % of O₃ in ozonised oxygen given that 18.8 ml of 0.1 thiosulphate solution is consumed by iodine liberated from KI in acid medium of 250 ml of sample at S.T.P..

To calculate the percentage of ozone (O₃) in ozonized oxygen, we need to follow a series of logical steps based on the information provided. The key here is to understand the relationship between the thiosulfate solution used and the amount of ozone present in the sample. Let's break this down step by step.

Understanding the Reaction

When ozone is present in a solution, it can react with potassium iodide (KI) in an acidic medium to liberate iodine (I₂). The reaction can be summarized as follows:

• O₃ + 2KI + 2H₂SO₄ → I₂ + 2KHSO₄ + H₂O

The liberated iodine can then be titrated with a sodium thiosulfate solution, which is what you have done in your experiment.

Calculating Moles of Thiosulfate

From the information given, we know that 18.8 mL of a 0.1 M thiosulfate solution was used. First, we need to calculate the number of moles of thiosulfate:

• Volume of thiosulfate solution = 18.8 mL = 0.0188 L
• Molarity of thiosulfate = 0.1 M
• Moles of thiosulfate = Molarity × Volume = 0.1 mol/L × 0.0188 L = 0.00188 moles

Relating Thiosulfate to Ozone

The stoichiometry of the reaction indicates that 1 mole of ozone reacts with 2 moles of thiosulfate. Therefore, the moles of ozone can be calculated as follows:

• Moles of O₃ = Moles of thiosulfate / 2 = 0.00188 moles / 2 = 0.00094 moles

Calculating Mass of Ozone

Next, we need to convert the moles of ozone to grams. The molar mass of ozone (O₃) is approximately 48 g/mol:

• Mass of O₃ = Moles × Molar Mass = 0.00094 moles × 48 g/mol = 0.04512 grams

Finding the Percentage of Ozone

Now, we need to find the percentage of ozone in the ozonized oxygen sample. The total volume of the sample is 250 mL, which is equivalent to 0.250 L. To find the density of the gas mixture, we can assume that the density of ozonized oxygen is similar to that of air, approximately 1.29 g/L. Thus, the mass of the 250 mL sample can be estimated:

• Mass of sample = Volume × Density = 0.250 L × 1.29 g/L = 0.3225 grams

Finally, we can calculate the percentage of ozone in the sample:

• Percentage of O₃ = (Mass of O₃ / Mass of sample) × 100 = (0.04512 g / 0.3225 g) × 100 ≈ 13.98%

Final Result

Therefore, the percentage of ozone in the ozonized oxygen sample is approximately 13.98%. This calculation illustrates the relationship between the amount of thiosulfate used in the titration and the concentration of ozone in the sample, providing a clear method for determining the percentage of ozone present.