Iodine, I2, reacts with aqueous thiosulfate ion in neutral solution according to the balanced equation How many grams of I2 are present in a solution if 35.20 mL of 0.150 M Na2S2O3 solution is needed to titrate the I2 solution?

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Step 1: Write down the balanced chemical equation for the reaction. In this case, the balanced equation is I2 + 2S2O3^2- -> 2I^- + S4O6^2-. This tells us that one mole of I2 reacts with two moles of S2O3^2-.

Step 2: Calculate the number of moles of S2O3^2- used in the titration. The number of moles can be calculated using the formula: moles = volume (in liters) x molarity. In this case, the volume of the Na2S2O3 solution used is 35.20 mL or 0.03520 L and the molarity is 0.150 M.

Step 3: Use the stoichiometry of the reaction to find the number of moles of I2. From the balanced equation, we know that 1 mole of I2 reacts with 2 moles of S2O3^2-. Therefore, the number of moles of I2 is half the number of moles of S2O3^2-.

Step 4: Convert the number of moles of I2 to grams. The molar mass of I2 is approximately 253.8 g/mol. Therefore, the mass in grams is calculated by multiplying the number of moles by the molar mass.

Step 5: The result from step 4 is the mass of I2 in the solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It involves using balanced chemical equations to determine the relationships between the amounts of substances consumed and produced. In this case, understanding the stoichiometric ratio between iodine (I2) and thiosulfate ions (S2O3^2-) is essential for calculating the amount of I2 present in the solution.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (M). In this problem, the molarity of the thiosulfate solution (0.150 M) is crucial for determining how many moles of thiosulfate are used in the titration, which can then be used to find the corresponding moles of iodine.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant (in this case, Na2S2O3) to a solution until the reaction reaches completion, indicated by a color change or another measurable endpoint. The volume of titrant used allows for the calculation of the amount of the analyte (I2) in the solution based on the stoichiometry of the reaction.

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