The pH of a solution is 2.57 at 25 degrees C. What is the molar concentration of hydronium ions? What is the molar concentration of hydroxide ions?

The pH of a solution is 2.57 at 25 degrees C.

What is the molar concentration of hydronium ions?
What is the molar concentration of hydroxide ions?

1 Answer
anor277
Sep 7, 2016

Given the definition of #pH#, I can write immediately that if #pH=2.57#, then #[H_3O^+]=10^(-2.57)# #mol*L^-1#

Explanation:

And also given the definitions, I know that #[H_3O^+][HO^-]=10^-14# under standard condtions; taking #log_10# of both sides, this gives our defining relationship:

#pH+pOH=14#

And thus #pOH# #=# #{14-2.57}#, and #HO^-# #=# #10^(-11.43)*mol*L^-1#.

Of course you will need a calculator to assess these values. I have never got one handy.

In a neutral solution at #298*K#, the equilibrium operates, #[H_3O^+][HO^-]=10^-14#, and #pH# #=# #pOH# #=# #7#. At temperatures higher than #298K#, how would you expect #pH# to evolve in a neutral solution. Would it increase, decrease, stay the same?

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