Suppose that you have 0.500 L of each of the following solutions, and an unlimited supply of water. (Note: C9H7NHBr is a salt containing the ions C9H7NH+ and Br− and C9H7N is quinoline, an organic base with pKb = 6.24 at 298 K. If you like, you may represent C9H7NH+ as HB+ and C9H7N as B.)
0.113 mol L−1 C9H7NHBr (aq) 0.104 mol L−1 HBr(aq) 0.122 mol L−1 NaOH(aq)
(a)Provide simple instructions for preparing 1.00 L of a solution having pH = 7.00 at 298 K. Your instructions should include the volumes of the solutions required.
(b) What is the buffer capacity of the resulting solution? (The buffer capacity is the number of moles of NaOH that must be added to 1.0 L of solution to raise the pH by one unit.)
Two questions.
1. Do you have the concns of the BH^+ and B?
2. What is the sentence 0.113 mol L−1 C9H7NHBr (aq) 0.104 mol L−1 HBr(aq) 0.122 mol L−1 NaOH(aq) I don't know what that has to do with the problem.
To prepare 1.00 L of a solution with a pH of 7.00 at 298 K, you'll need to use the given solutions and dilute them as required. Here are the step-by-step instructions:
(a) Instructions for preparing the solution with pH = 7.00:
Step 1: Calculate the required ratio of HB+ to B for a pH of 7.00.
- pH = pKa + log([B]/[HB+])
- Since pKa = 14 - pKb, and pKb = 6.24:
- 7.00 = 14 - 6.24 + log([B]/[HB+])
Step 2: Use the Henderson-Hasselbalch equation to calculate the ratio [B]/[HB+] for a pH of 7.00.
- pH = pKa + log([B]/[HB+])
- Rearrange the equation:
- [B]/[HB+] = 10^(pH - pKa)
Step 3: Calculate the moles of HB+ required.
- Moles of HB+ = concentration of HB+ in mol/L × volume of solution desired in L
Step 4: Calculate the volume of C9H7NHBr (aq) required.
- Volume of C9H7NHBr (aq) = Moles of HB+ required / concentration of C9H7NHBr (aq) in mol/L
Step 5: Calculate the volume of HBr (aq) required.
- Volume of HBr (aq) = Volume of C9H7NHBr (aq) required
Step 6: Calculate the volume of NaOH (aq) required.
- Volume of NaOH (aq) = (Volume of C9H7NHBr (aq) required + Volume of HBr (aq) required) / 2
Step 7: Dilute the solution to 1.00 L with water.
- Add water in the amount necessary to reach a final volume of 1.00 L.
(b) To calculate the buffer capacity of the resulting solution:
- Buffer capacity = (moles of NaOH required to raise the pH by one unit) / (volume of solution in L)
Please note that for more accurate calculations, molecular weights should be considered to convert moles to mass or vice versa. You can find the molecular weights of the substances involved to perform those conversions.