50 ml of 0.001M phosphoric acid is exactly neutralised by addition of 0.005N NaOH.the molarity of resulting salt solution is

To determine the molarity of the resulting salt solution after neutralizing phosphoric acid with sodium hydroxide, we need to first understand the reaction that occurs between these two substances. Phosphoric acid (H₃PO₄) is a triprotic acid, meaning it can donate three protons (H⁺ ions), while sodium hydroxide (NaOH) is a strong base that can accept these protons. Let's break down the steps to find the molarity of the resulting salt solution.

Step 1: Calculate Moles of Phosphoric Acid

First, we need to calculate the number of moles of phosphoric acid present in the solution. The formula for calculating moles is:

Moles = Molarity × Volume

Given that the molarity of phosphoric acid is 0.001 M and the volume is 50 ml (which is 0.050 L), we can calculate the moles:

• Moles of H₃PO₄ = 0.001 M × 0.050 L = 0.00005 moles

Step 2: Determine the Equivalent of Phosphoric Acid

Since phosphoric acid is triprotic, each mole can donate three protons. Therefore, the number of equivalents of phosphoric acid is:

• Equivalents of H₃PO₄ = 0.00005 moles × 3 = 0.00015 equivalents

Step 3: Calculate Moles of Sodium Hydroxide

Next, we need to find out how many moles of sodium hydroxide were used in the neutralization. The normality (N) of NaOH is given as 0.005 N. Since NaOH is a strong base that provides one hydroxide ion (OH⁻) per molecule, its molarity is equal to its normality:

• Moles of NaOH = Normality × Volume
• Volume of NaOH = 0.005 N × 0.050 L = 0.00025 moles

Step 4: Neutralization Reaction

The neutralization reaction can be represented as:

H₃PO₄ + 3 NaOH → Na₃PO₄ + 3 H₂O

From the balanced equation, we see that 1 mole of H₃PO₄ reacts with 3 moles of NaOH. Since we have 0.00015 equivalents of H₃PO₄, it will react with:

• 0.00015 equivalents of H₃PO₄ require 0.00015 × 3 = 0.00045 moles of NaOH.

However, we only have 0.00025 moles of NaOH available, which means NaOH is the limiting reagent in this reaction.

Step 5: Calculate Moles of Salt Formed

Since NaOH is limiting, we can calculate the moles of salt (sodium phosphate, Na₃PO₄) formed based on the moles of NaOH used:

• From the reaction, 3 moles of NaOH produce 1 mole of Na₃PO₄.
• Moles of Na₃PO₄ = 0.00025 moles NaOH × (1 mole Na₃PO₄ / 3 moles NaOH) = 0.0000833 moles Na₃PO₄.

Step 6: Calculate Total Volume of the Solution

After the reaction, the total volume of the solution will be the sum of the volumes of the phosphoric acid and sodium hydroxide solutions:

• Total Volume = 50 ml (H₃PO₄) + 50 ml (NaOH) = 100 ml = 0.1 L.

Step 7: Find the Molarity of the Resulting Salt Solution

Finally, we can calculate the molarity of the sodium phosphate solution using the formula:

Molarity = Moles of solute / Volume of solution in liters

• Molarity of Na₃PO₄ = 0.0000833 moles / 0.1 L = 0.000833 M.

Thus, the molarity of the resulting salt solution is approximately 0.000833 M.