Question

5. The pH of HCl is 5. It is diluted by 1000 times
Its pH will be​

Answer 1

by concept of millimoles

M1*V1 = M2*V2

since pH = 5 , so concentration of H+ is molarity = 10^-5M , V2 = 1000*V1

so M2 =10^-8 but since [H+] = 10^-8

pH = 8 [can not be 8 for acid ]

so here when concentration of HCl is less than 10^-6M , we have to consider concentration of H+ = 10^-7M from water.

so Total [H+] = 10^-7 +10^-8

[H+] = 1.1*10^-7

now take negative of logarithm to base 10

pH = 7 - log(1.1 with base 10)

pH = 7 -0.04 = 6.96

Answer 2

pH of HCl would be 7.