URGENT!!! How many grams of sodium benzoate (NaC6H5CO2) must be added to 500 mL of 0.15 M benzoic acid (HC6H5CO2) to make a buffer solution with pH of 5.0? Assume no volume change upon sodium benzoate dissolution. Ka = 6.46 x 10-5
How would I go about this question?
Use the Henderson-Hasselbalch equation
To solve this question, you need to understand the concept of a buffer solution and how it works.
A buffer solution is a solution that can resist changes in its pH when small amounts of acid or base are added to it. It consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in similar concentrations.
In this case, you are given a solution of benzoic acid (HC6H5CO2), which is a weak acid, and you need to add sodium benzoate (NaC6H5CO2), its conjugate base, to create a buffer with a pH of 5.0.
Here's how you can approach this problem step by step:
1. Write down the balanced equation for the dissociation of benzoic acid in water:
HC6H5CO2 ↔ H+ + C6H5CO2-
2. Use the given value of the Ka (acid dissociation constant) to calculate the concentration of H+ ions in the solution. The Ka expression for benzoic acid is:
Ka = [H+][C6H5CO2-] / [HC6H5CO2]
You know the value of Ka and the concentration of the weak acid ([HC6H5CO2]), so you can solve for [H+] using this equation.
3. To create a buffer with a pH of 5.0, you need to calculate the ratio of the concentration of [HC6H5CO2] to [C6H5CO2-].
For a pH of 5.0, the ratio [HC6H5CO2]/[C6H5CO2-] should be 10:1 (as pH is calculated based on log[H+], which is approximately 10 times higher for pH 5 compared to pH 4).
4. Since you know the initial volume of the solution (500 mL) and the concentration of the weak acid (0.15 M), you can calculate the moles of benzoic acid (HC6H5CO2) present in the solution.
5. Now you can determine the required amount of sodium benzoate (NaC6H5CO2) needed to be added to the solution to achieve the desired buffer ratio. Since the volume does not change upon sodium benzoate dissolution, the moles of sodium benzoate will be equal to the moles of benzoic acid.
6. Convert the moles of sodium benzoate to grams by multiplying by its molar mass.
By following these steps, you can find the required grams of sodium benzoate needed to make a buffer solution with a pH of 5.0.