Determine the pH (to two decimal places) of a solution prepared by adding 395 mL of 0.0360 M benzoic acid (C6H5COOH) to 12.5 g of sodium benzoate (NaC6H5COO).
Use the Henderson-Hasselbalch equation.
Sodium benzoate is the base and benzoic acid is the acid.
To determine the pH of the solution, you need to understand the concept of acid-base reactions and how to calculate the pH using the concentration of hydrogen ions (H+).
1. Start by writing down the balanced equation for the reaction between benzoic acid (C6H5COOH) and sodium benzoate (NaC6H5COO):
C6H5COOH + NaC6H5COO → C6H5COO- + Na+ + H2O
2. Now, calculate the moles of benzoic acid and sodium benzoate:
Moles of benzoic acid = volume (in liters) × concentration
Moles of benzoic acid = 0.395 L × 0.0360 M
Moles of sodium benzoate = mass ÷ molar mass
Moles of sodium benzoate = 12.5 g ÷ (109.1 g/mol + 22.99 g/mol + 72.1 g/mol)
3. Determine the limiting reagent. The reactant that generates fewer moles of product is the limiting reagent. In this case, the limiting reagent is benzoic acid because it generates one mole of C6H5COO- for every mole used, while sodium benzoate generates one mole of C6H5COO- for each mole used.
4. Calculate the moles of C6H5COO- produced by the limiting reagent:
Moles of C6H5COO- = moles of benzoic acid
5. From the balanced equation, you can see that for every mole of C6H5COOH that reacts, one mole of H+ is also produced. Thus, the moles of C6H5COO- is equal to the moles of H+.
6. Convert moles of H+ to concentration by dividing the moles by the volume of the solution in liters:
Concentration of H+ = moles of H+ ÷ volume of the solution (in liters)
Concentration of H+ = moles of C6H5COO- ÷ total solution volume (in liters)
Total solution volume = volume of benzoic acid + volume of sodium benzoate
7. Finally, calculate the pH using the concentration of H+:
pH = -log[H+]
Plug in the concentration of H+ calculated in step 6 and solve for pH. Round your answer to two decimal places.
Following these steps, you should be able to determine the pH of the solution.