Calculating pH Change from HClO4 Addition

[answerseeker]

when you add 10.0 mL of 1.0M HClO4 into 990.0mL water, the pH changes by 2.
how would you find the change in pH?

 

[Gokul43201]

1. Write out the expression that defines pH
2. Assume HClO4 is close to 100% dissociated in solution
3. From the original concentration of HClO4, find [H+] and calculate the original pH from this

4. Calculate the new (diluted) concentration of HClO4 (molarity = number of moles/volume of solution)
5. Using the new value of [H+], calculate pH again.
6. Subtract from the original number to find the difference.