Assume you dissolve 0.235 g of the weak acid benzoic acid, C6H5CO2H, in enough water to make 4.00*10^2 mL of solution and then titrate the solution with 0.138 M NaOH.
C6H5CO2H(aq) + OH-(aq) C6H5CO2-(aq) + H2O(l)
Find concentration of Na+ at equivalence point.
To find the concentration of Na+ at the equivalence point, we first need to determine the number of moles of benzoic acid (C6H5CO2H) in the solution. Then, we can use stoichiometry to calculate the number of moles of Na+ ions present at the equivalence point.
1. Calculate the number of moles of benzoic acid (C6H5CO2H):
- Given mass of benzoic acid = 0.235 g
- Formula weight of benzoic acid (C6H5CO2H) = 122.12 g/mol
- Number of moles of benzoic acid = mass / formula weight
= 0.235 g / 122.12 g/mol
2. Calculate the volume of the solution in liters:
- Given volume of solution = 4.00*10^2 mL
- Convert mL to liters: 4.00*10^2 mL / 1000 mL/L
3. Calculate the concentration of benzoic acid (C6H5CO2H) in the solution:
- Concentration (molarity) = moles / volume
4. Use the balanced equation to determine the stoichiometry between benzoic acid (C6H5CO2H) and Na+ ions:
- From the balanced equation, we know that 1 mole of benzoic acid reacts with 1 mole of Na+ ions.
5. Therefore, at the equivalence point, the number of moles of Na+ ions is equal to the number of moles of benzoic acid.
6. Convert the number of moles of Na+ ions to concentration:
- Concentration (molarity) = moles / volume
Follow these steps, plug in the given values, and perform the calculations to find the concentration of Na+ at the equivalence point.
To find the concentration of Na+ at the equivalence point, we need to calculate the moles of benzoic acid (C6H5CO2H) and NaOH that are involved in the reaction.
1. Calculate the number of moles of benzoic acid:
- Given the mass of benzoic acid is 0.235 g.
- The molar mass of benzoic acid (C6H5CO2H) is 122.12 g/mol.
- Number of moles = mass / molar mass = 0.235 g / 122.12 g/mol.
2. Determine the volume of the benzoic acid solution:
- Given the volume of the solution is 4.00 * 10^2 mL, which is equivalent to 0.4 L.
3. Calculate the concentration of the benzoic acid solution in mol/L:
- Concentration (C) = moles / volume in L = (0.235 g / 122.12 g/mol) / 0.4 L.
4. Use the balanced equation to determine the stoichiometry between benzoic acid and NaOH:
- From the equation: 1 mol of benzoic acid reacts with 1 mol of NaOH.
5. Determine the moles of NaOH at the equivalence point:
- The volume of NaOH used at the equivalence point can be obtained from the titration data, and let's assume it is V NaOH.
6. Use the concentration of NaOH (0.138 mol/L) and the volume V NaOH to calculate the moles of NaOH:
- Moles of NaOH = concentration * volume in L = 0.138 mol/L * V NaOH.
7. Since the stoichiometry between benzoic acid and NaOH is 1:1, the moles of NaOH are equal to the moles of Na+ produced.
So, the concentration of Na+ at the equivalence point is equal to the moles of NaOH divided by the total volume of the benzoic acid solution:
Concentration of Na+ at the equivalence point = Moles of NaOH / Total volume of the solution.