Equal volumes of two solutions of HCl are mixed. One solution has pH = 1
while the other has pH = 5. What will the pH of the solution obtained be?
Solution:
Let the volume of the solutions mixed = “V” mL
So, the volume of the final solution obtained after mixing = “2V” mL
For solution with pH = 1,
Concentration of H+ = 10-1 M
Moles of H+ = 10-1 V
For solution with pH = 5,
Concentration of H+ = 10-5M
Moles of H+ = 10-5 V
For the Final Solution,
Total moles of H+ in the final solution
= (10-1 V) + (10-5 V) ≈ 10-1 V
Concentration of H+ in the final solution
= (10-1 V) / 2V = 0.05 M
pH of the final solution = -log 0.05 = 1.3