Virtual Laboratory Activity - Preparing and testing your buffer solution Prepare the buffer solution - In this task, your will prepare the buffer solution described in point 1 of the Experimental Procedure in the Expermimental overview (D1). The required calculations are similar to the calculations on the previous pages of this tutorial. Using the chemicals provided in the Virtual Lab stockroom, prepare 100 mL of the calculated buffer solution in a 100 mL volumetric flask. Transfer the calculated amount of NaH2PO4 (weak acid) to a 100 mL volumetric flask. Add 1.0 M NaOH (strong base) until the desired pH has been obtained. Fill the volumetric flask to the mark with water. Please answer the first set of questions below the virtual lab. Checking the capacity of the buffer - Check the buffer capacity on a 25 mL sample of this buffer. Pour 25 mL of the buffer into a flask or beaker. Add 0.10 M HCl or 0.10 M NaOH to your buffer solution until the pH changes by 1 unit. Please answer the second set of questions below the virtual lab. How many mL of NaH2PO4 did you use? 35 mL How many mL of 1.0 M NaOH did you use in your virtual laboratory experiment to reach the target pH of 7.45? 11.36 mL [H2PO4-] = 0.5 M [HPO4-2] = 0.5 M

q1.How many mL of HCl were required to lower the pH by 1 unit?

q2.Calculate the number of moles of HCl required to lower the pH of 1.0 L buffer solution by 1 unit.

A buffer solution is created in which the concentration of weak acid [HA] = 0.90 M and the concentration of conjugate base [A-] = 1.0M. The volume of the solution is 100 mL and the pH is 4.3. Please indicate how each of the following procedures will affect the pH and buffer capacity of this buffer solution.

1. Addition of 5.0 mL each of 10M HA and 10M NaA

2. Addition of 50 mL distilled water

3. Evaporation until the volume is 50 mL

4. Addition of 5.0 mL of 1.0 M NaOH and 5.0 mL of 1.0 M HCl

q3. A buffer solution is created in which the concentration of weak acid [HA] = 0.90 M and the concentration of conjugate base [A^-] = 1.0M. The volume of the solution is 100 mL and the pH is 4.3.

Which of the following statements is true regarding the buffer solution mentioned ? (More than one statement can be true). 1.The buffer capacity for addition of acid is greater than that for addition of base 2. The pKa of HA is greater than 4.3

3. A mixture of HA and A^- is a good choice for a buffer that mimics blood 4. Slowly adding 10M HCl to the solution until the pH is 4.5 will lead to a good buffer with pH=4.5

q4.A student at another university was asked to define buffer capacity. The answer given was: the concentration of weak acid plus the concentration of conjugate base ([HA] + [A-]). How good is this definition, i.e. what aspects of buffer capacity (if any) does it capture and what aspects (if any) does it miss?