Can someone help me by calculating change in pH?

50mL of water is added to 20 mL of a 0.50 mol/L solution of hydrochloric acid. Have to calculate the change in pH that occurs. How do you write the ? and figure it out?Can someone help me by calculating change in pH?
C1V1 = C2V2



where:

C1 - concentration 1

V1 - volume 1

C2 - concentration after dilution

V2 - volume after dilution



HCl is a strong acid where the concentration of the acid, [HCl], would be equal to the hydronium ion concentration, [H+]



1st pH = -log(0.5) = 0.301



use the first equation for dilution:



(0.5mol/L)(20mL) = C2(20mL + 50mL)

(0.5mol/L)(20mL) = C2(70mL)

[(0.5mol/L)(20mL)]/(70mL) = C2 = 0.1429mol/L



2nd pH = -log(0.1429) = 0.8451



the change in pH = 0.8451 - 0.301 = 0.5441



the dilution of the acid to 70mL would indicate a decrease in hydronium ion concentration thus it would result in a high pH value (more basic).Can someone help me by calculating change in pH?
What so rt of level are you asking this question at? At advanced levels you may have to take into account ion activities, non ideal solutions and the like.



However, on a simple level



How many moles of HCl do you have to start with? What volume do you end up with? So what is the concentration of H+, and hence, what is the pH