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^{-5}M
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 MpH of the final solution = -log 0.05 = 1.3