question 5 on Test 2


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Joanna Pham - 2D
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Joined: Fri Apr 06, 2018 11:04 am

question 5 on Test 2

Postby Joanna Pham - 2D » Sun Mar 10, 2019 4:53 pm

This problem asked us to determine if a pH = 7 is acidic or basic when the temperature went from 25 Celsius to 10 C. Standard enthalpy was 58 kJ/mol and Kw at 25 Celsius = 10^-14, and the equation was

Does anyone happen to know how to determine if a pH of 7 is either acidic or basic when the temperature went from 25 celsius to 10 C??

WilliamNguyen_4L
Posts: 65
Joined: Fri Sep 28, 2018 12:28 am

Re: question 5 on Test 2

Postby WilliamNguyen_4L » Sun Mar 10, 2019 5:01 pm

You would use the Van't Hoff equation, ln(K2/K1)=-(deltaH/R)*((1/T2)-(1/T1))to find the Kw of water at 10 C. convert 25 c and 10 c to kelvin and then plug in the given values to find K2. The sqaure root of K2 would be the concentration of H+ and taking the negative log would give u the ph of water at 10 C. This would be lower than 7 so a ph of 7 at 10 C would be higher than the ph of water at 10 C so the ph of 7 would be basic.

hannahdaijo_4H
Posts: 48
Joined: Fri Sep 28, 2018 12:27 am

Re: question 5 on Test 2

Postby hannahdaijo_4H » Sun Mar 10, 2019 5:31 pm

The negative log of the H+ concentration essentially gives you the new "neutral" pH at the second temperature. So as was said above, pH 7 > pH x, so pH 7 is basic


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