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Test #2 Question 5 (ph acidic or basic)

Posted: Sat Mar 09, 2019 6:25 pm
by Nathaniel 2E
This question from Test #2 baffled me, I still don't know what was the correct way to approach it:

The ionic dissociation of water is given by the following reaction: The deltaHo for the reaction is 58 kJ/mol. The Kw for the reaction at 25 degrees C is 10^-14. Is a pH of 7 acidic or basic at 10 degrees C?

How were you supposed to solve this problem? Which equations do you use? The thing I couldn't figure out was what we were even solving for...

Re: Test #2 Question 5 (ph acidic or basic)

Posted: Sat Mar 09, 2019 6:41 pm
by Emily Huang 1E
For this question you use the equation of ln(K2/K1)=delta H/R (1/T2 - 1/T1) . K1 is 10^-14 and T1 is 25 degrees celsius. You plug in delta H=58 kj/mol and plug in T2=10 degrees celsius or 283K. You plug in all values to find K2. K2 is equal to the concentration of H30+ and OH-. You know that the concentration of H30+ is 10^-7 since the pH is 7. Then you solve for the concentration of OH-. If the pOH is greater than the pH then the reaction is basic at pH7. If pOH is less than the pH, then the reaction is acidic at pH7.