How to make 0.086M sodium phosphate when combined with 0.1N HCl has a pH of 6.2?
To understand how to make a 0.086M sodium phosphate solution that, when combined with 0.1N HCl, has a pH of 6.2, we need to consider the acid-base properties of sodium phosphate and HCl.
First, let's start by understanding what the terms "0.086M" and "0.1N" mean:
- "0.086M" represents the molarity (M) of the sodium phosphate solution. Molarity refers to the concentration of a solution, i.e., the number of moles of solute dissolved in one liter of solvent. So, 0.086M sodium phosphate means that there are 0.086 moles of sodium phosphate dissolved in each liter of solution.
- "0.1N" represents the normality (N) of the HCl solution. Normality measures the equivalent concentration of an acid or base, which takes into account its acid-base properties and reaction stoichiometry. In this case, 0.1N HCl means that the HCl solution is equivalent to 0.1 moles of HCl per liter of solution.
Now, let's focus on the pH of the final solution. The pH scale measures the acidity or basicity of a solution. A pH of 6.2 indicates a slightly acidic solution.
To make the desired solution, we need to consider how sodium phosphate and HCl interact. Sodium phosphate is a basic compound, while HCl is an acidic compound. When they react, the phosphate ion (PO4^-3) from sodium phosphate can react with the H+ ions from HCl, forming H3PO4 (phosphoric acid) and neutralizing some of the acidity.
Here's a step-by-step guide to make the desired solution:
1. Calculate the molar ratio: The balanced equation for the reaction between sodium phosphate (Na3PO4) and HCl is:
3Na3PO4 + xHCl → 3H3PO4 + xNaCl
The coefficient 'x' represents the amount of HCl required to react with sodium phosphate. To balance the equation, we need 'x' moles of HCl for every 3 moles of Na3PO4.
2. Calculate the moles of sodium phosphate (Na3PO4): We want a concentration of 0.086M for sodium phosphate. Therefore, if we want to make 1 liter of the solution, we'll need 0.086 moles of Na3PO4.
3. Calculate the moles of HCl required: Using the molar ratio from step 1, determine the number of moles of HCl needed to react with the calculated moles of sodium phosphate.
4. Calculate the volume of the HCl solution: Since the HCl concentration is given as 0.1N, this means that every liter of the solution contains 0.1 moles of HCl. Use this information to calculate the volume of the HCl solution required to obtain the calculated moles of HCl.
5. Prepare the solution: Measure out the calculated moles of sodium phosphate, dissolve it in water, and then add the calculated volume of the HCl solution. Ensure to mix them thoroughly.
By following these steps, you should be able to prepare a 0.086M sodium phosphate solution that, when combined with 0.1N HCl, results in a final solution with a pH of 6.2.