How many milliliters of 0.250 M Na2S2O3 solution is needed for complete reaction with 2.486 g of I2 according to the equation in Problem 4.124?

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Identify the balanced chemical equation for the reaction between \( \text{Na}_2\text{S}_2\text{O}_3 \) and \( \text{I}_2 \). Typically, the reaction is: \[ \text{I}_2 + 2 \text{Na}_2\text{S}_2\text{O}_3 \rightarrow 2 \text{NaI} + \text{Na}_2\text{S}_4\text{O}_6 \]

Calculate the moles of \( \text{I}_2 \) using its molar mass. The molar mass of \( \text{I}_2 \) is approximately 253.8 g/mol. Use the formula: \[ \text{moles of } \text{I}_2 = \frac{\text{mass of } \text{I}_2}{\text{molar mass of } \text{I}_2} \]

Use the stoichiometry of the balanced equation to find the moles of \( \text{Na}_2\text{S}_2\text{O}_3 \) needed. According to the equation, 1 mole of \( \text{I}_2 \) reacts with 2 moles of \( \text{Na}_2\text{S}_2\text{O}_3 \).

Calculate the volume of \( 0.250 \text{ M } \text{Na}_2\text{S}_2\text{O}_3 \) solution required using the formula: \[ \text{Volume (L)} = \frac{\text{moles of } \text{Na}_2\text{S}_2\text{O}_3}{\text{Molarity of } \text{Na}_2\text{S}_2\text{O}_3} \]

Convert the volume from liters to milliliters by multiplying by 1000, since 1 L = 1000 mL.

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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 branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. It allows us to calculate how much of a substance is needed or produced in a reaction based on the balanced chemical equation. Understanding stoichiometry is essential for determining the amount of Na2S2O3 required to react with a given mass of I2.

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 question, the molarity of the Na2S2O3 solution (0.250 M) is crucial for calculating the volume needed to completely react with the specified mass of iodine (I2).

Molecular Weight

Molecular weight, or molar mass, is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To find out how many moles of I2 are present in 2.486 g, one must first calculate its molecular weight (approximately 253.8 g/mol). This information is necessary to relate the mass of I2 to the stoichiometric amount of Na2S2O3 needed for the reaction.

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