Dilution and Mixing
Problem 1: Dilution of Sulfuric Acid
40 mL of 2.5 molar H2SO4 solution will be diluted to 2 L. What is the pH of the diluted solution?
Answer
Before we enter the parameters into the program, please recap: The dilution factor is
2000 mL / 40 mL = 50
Hence, the diluted solution contains exactly (2500 mM / 50) = 50 mM H2SO4.
Switch to pure water (button H2O), then click on Reac and enter for “H2SO4” the value 50 mM.
After clicking on Start the program outputs the result (see right screenshot):
pH = 1.27
The diluted solution has pH 1.27.
Note. If you would solve this task with a pocket calculator, you would get a pH value of 1.3. The deviation from the correct result (pH 1.27) is caused by activity corrections for non-ideal solutions.
Problem 2: Mixing HCl with NaOH
100 mL of 0.01 molar HCl is mixed with 50 mL of 0.05 molar NaCl. What is the pH of the final solution?
Answer
We begin with pure water (button H2O), then click on Reac and activate the checkbox More Reactions.
Before we enter the parameters, please recap: The final volume is 150 mL (= 100 mL + 50 mL) and, thus, the mixing solution contains:
| ( 100 mL / 150 mL ) × 10 mM = 6.67 mM HCl |
| ( 50 mL / 150 mL ) × 50 mM = 16.7 mM NaOH |
Run the calculation with Start. The result is shown on the right screenshot: The mixed solution has pH 11.94.