- #1

- 62

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in a lecture entitled "calculating the pH of a strong acid/base solution " after adding a certain amount of HCl in water we are asked to calculate the pH

(the amount of HCl and volume of water is known )

*to calculate the pH we need to calculate [H3O+]

*we have 2 sources of [H3O+] in this solution

-first the [H3O+] from HCl

-second the [H3O+] from the dessosiation of water

we know that [H3O+]from HCl=[Cl-] because HCl is a strong acid

and we reffered to the [H3O+] from water as [OH-] ( here is the problem but we'll come back to it later )

using Kw we replaced [OH-] with (10^-14/[H3O+])

now we have this equation [H3O+]=(10^-14/[H3O+]) +[Cl-]

and the professor said that all we need to do is to solve the quadratic equation

here is the problem it seem that the two [H3O+] are not the same unknown ( the amount of [H3O+] from water do not equal to (10^-14/[H3O+])) , here is a plot