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

How many mL of HCl were required to lower the pH by 1 unit? Calculate the number of moles of HCl required to lower the pH of 1.0 L buffer solution by 1 unit.