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.)
Data
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.)
Question 2)
Ethylamine, CH3CH2NH2, is an organic base with pKb= 3.367 at 298 K. In an experiment, a 40.0 mL sample of 0.105 mol L-1CH3CH2NH2(aq) is titrated with 0.150 mol L-1HI(aq) solution at 298 K.
(a) Write a balanced chemical equation for the neutralization reaction upon which this titration is based, and indicate clearly which atom is being protonated. Then, calculate the equilibrium constant for the neutralization reaction. (Hint: To calculate the equilibrium constant, you may find it helpful to represent the neutralization reaction as the sum of two separate reactions.)
(b) Calculate the pH, [CH3CH2NH2], and [CH3CH2NH3+] at the following stages of the titration.
i) before the addition of any HI solution.
ii) after the addition of 20.0 mL of HI solution.
iii) at the equivalence point.
iv) after the addition of 60.0 mL of HI solution.