4. A student is asked to prepare a buffer solution made with equimolar amounts of CH3NH2(aq) and CH3 — Buffers, Acid-Base Equilibria, Experimental Design Chemistry Question
Problem Context
- A student is asked to prepare a buffer solution made with equimolar amounts of CH3NH2(aq) and CH3NH3Cl(s). The student uses 25.00 mL of 0.100 M CH3NH2(aq), which contains 0.00250 mol of CH3NH2, to make the buffer.
(a) Calculate the mass of CH3NH3Cl(s) that contains 0.00250 mol of CH3NH3Cl.
The student has the following materials and equipment available.
• Distilled water
• 0.100 M CH3NH2(aq)
• Solid CH3NH3Cl
• Electronic balance
• Weighing paper
• 50.00 mL buret
• 50 mL beaker
• 10.0 mL graduated cylinder
• Small spatula
• Pipets
• pH meter
(b) The following table contains a partial procedure for making the buffer solution. Fill in steps 1 and 4 to complete the procedure using only materials and equipment selected from the choices given. (Not all materials listed will be used. Assume that all appropriate safety measures are already in place.)
The value of Kb for CH3NH2(aq) is 4.4 × 10^-4, and the pH of the buffer the student prepared is 10.64.
(c) The student prepares a second buffer solution. The student uses 25.00 mL of 0.050 M CH3NH2(aq) instead of 25.00 mL of 0.100 M CH3NH2(aq), and half the mass of CH3NH3Cl(s) that was used in the first buffer. Is the pH of the second buffer greater than, less than, or equal to the pH of the first buffer? Justify your answer.