25 ml of solution of Fe2+ ions was titrated with a solution of the oxidizing agent Cr2O72- ,50 ml of 0.01 M K2Cr2O7 solution was required . what is the molarity of the Fe2+ solution ?

To determine the molarity of the Fe²⁺ solution, we first need to understand the stoichiometry of the reaction between Fe²⁺ ions and the dichromate ions (Cr₂O₇^2-). The balanced chemical equation for this redox reaction is as follows:

Balanced Reaction

The reaction can be represented as:

6 Fe²⁺ + Cr₂O₇^2- + 14 H⁺ → 6 Fe³⁺ + 2 Cr³⁺ + 7 H₂O

Understanding Molarity and Stoichiometry

Molarity (M) is defined as the number of moles of solute per liter of solution. To find the molarity of the Fe²⁺ solution, we need to follow these steps:

• Calculate the moles of K₂Cr₂O₇ used in the titration.
• Use the stoichiometry of the balanced equation to find the moles of Fe²⁺ that reacted.
• Calculate the molarity of the Fe²⁺ solution using the volume of the Fe²⁺ solution.

Step 1: Calculate Moles of K₂Cr₂O₇

The molarity of the K₂Cr₂O₇ solution is given as 0.01 M, and the volume used is 50 mL (which is 0.050 L). To find the moles:

Moles of K₂Cr₂O₇ = Molarity × Volume = 0.01 mol/L × 0.050 L = 0.0005 moles

Step 2: Relate Moles of Cr₂O₇^2- to Moles of Fe²⁺

From the balanced equation, we see that 1 mole of Cr₂O₇^2- reacts with 6 moles of Fe²⁺. Therefore, the moles of Fe²⁺ can be calculated as:

Moles of Fe²⁺ = 6 × Moles of Cr₂O₇^2- = 6 × 0.0005 = 0.0030 moles

Step 3: Calculate Molarity of Fe²⁺ Solution

Now that we have the moles of Fe²⁺, we can find its molarity. The volume of the Fe²⁺ solution is 25 mL (or 0.025 L). Using the molarity formula:

Molarity of Fe²⁺ = Moles of Fe²⁺ / Volume of solution (L)

Molarity of Fe²⁺ = 0.0030 moles / 0.025 L = 0.12 M

Final Result

The molarity of the Fe²⁺ solution is 0.12 M. This means that in every liter of the Fe²⁺ solution, there are 0.12 moles of Fe²⁺ ions present. Understanding these calculations is crucial for accurately determining concentrations in titration experiments.