Test 2 Question 5


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Kassidy Tran 1E
Posts: 77
Joined: Fri Sep 28, 2018 12:15 am

Test 2 Question 5

Postby Kassidy Tran 1E » Sat Mar 16, 2019 9:53 pm

I'm having problems understanding what the correct answer for test 2 question 5 is. The question asks whether the pH of & is acidic/basic at 10C, and I have been told to do this problem multiple ways, both with differing answers. One way to solve the problem as I have been told is to find the [H+] concentration and the [OH-] concentration at pH = 7 at 10C, and compare the two, seeing whether [OH-] < [H+] or [OH-] > [H+], and determining the basicity or acidity that way. Another method I have been told to do is to find the new pH and compare it to 7, and if it is higher/lower than 7 then that determines whether 7 is basic or acidic. The first method says the pH of 7 is basic at 10C and the second method says the pH of 7 is acidic at 10C. Which is the correct method and answer, and why?

Srikar_Ramshetty 1K
Posts: 64
Joined: Fri Sep 28, 2018 12:27 am

Re: Test 2 Question 5

Postby Srikar_Ramshetty 1K » Sat Mar 16, 2019 9:59 pm

The correct answer is that the pH of 7 is basic at the new temperature. This is because the new neutral pH decreses to approx. 6.8. Since 7 is greater than that it will be basic. Hope that helps.

Maayan Epstein 14B
Posts: 39
Joined: Fri Sep 28, 2018 12:20 am

Re: Test 2 Question 5

Postby Maayan Epstein 14B » Sat Mar 16, 2019 10:02 pm

The second method is correct. I am not sure how you solved the first method, but you use the equation ln(k2/K1)= RT(1/T2 -1/T1) to solve for K2. Then you use K2 to find the concentration of H+. The equilibrium concentration of H+ at 10 degrees C for a neutral solution (we know it is neutral because it is made up of buffers) is higher than 7. Therefore, a pH of 7 is lower than this new scaled value and therefore it is acidic. I hope that makes sense! Good luck;

arif_latif_2G
Posts: 60
Joined: Fri Sep 28, 2018 12:23 am

Re: Test 2 Question 5

Postby arif_latif_2G » Sat Mar 16, 2019 10:06 pm

From what I understand, you should compare the pH at the new temperature to 7. If it is less than 7, consider it as acidic. Since pH is based on the concentration of H+, you shouldn't compare it the OH- concentration.

Karina Jiayu Xu 4E
Posts: 58
Joined: Fri Sep 28, 2018 12:29 am

Re: Test 2 Question 5

Postby Karina Jiayu Xu 4E » Sun Mar 17, 2019 12:53 am

u guys reply with different answers. did lavelle ever post the solution? where can i find the solution?

hanna_maillard3B
Posts: 61
Joined: Fri Sep 28, 2018 12:23 am

Re: Test 2 Question 5

Postby hanna_maillard3B » Sun Mar 17, 2019 1:12 am

what do you use a k1 value ? how do you calculate k2 when we're only given kw ?


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