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Chapter 6: Acids and Bases

Re: Chapter 6: Acids and Bases

Postby goldstanda3269 » Sat Feb 13, 2021 10:36 am

Laura_2707 wrote:Hi

Im just wondering about question 16.
Would you be able to talk me through it in a bit more detail? I don't understand the solution given!
How do you arrive at [A-]/[HA] = 10-3 ?


Thank you!


Masters Series GAMSAT Question 16

The question stem mentions pKa and pH so we need to find a way that they relate. The passage provides that relationship by describing the Henderson-Hasselbach equation:

pH = pKa + log([A-]/ [AH])

The question stem describes this relationship: [A-]/[HA] = 1/10^3 = 10^-3. We are also told that the pKa is 5.

Substituting:

pH = pKa + log([A-]/ [AH]) = 5 + log (10^-3) = 5 - 3 = 2
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Re: Chapter 6: Acids and Bases

Postby SarahMcKenna » Thu Feb 18, 2021 12:48 am

Hi, for Q21 i dont understand the log explanation of -log ka to be -log (4x10-4) if Ka was given as 2.0x10^-4?
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Re: Chapter 6: Acids and Bases

Postby goldstanda3269 » Thu Feb 18, 2021 11:19 pm

SarahMcKenna wrote:Hi, for Q21 i dont understand the log explanation of -log ka to be -log (4x10-4) if Ka was given as 2.0x10^-4?


That is a typo. It will be updated within 24 hours (though of course, it does not change the answer or the reasoning in the worked solution). Good pick up!
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Re: Chapter 6: Acids and Bases

Postby zimengy17106 » Sun Feb 28, 2021 9:03 pm

Hi,

I have a question on Q15. I chose C because I thought statement II is not correct?

Statement II: The higher the PH, the greater the activity of carbonic anhydrase. However, carbonic anhydrase is an enzyme so has an optimal PH. If PH too high, the enzyme will be deactivated?

Thanks!
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Re: Chapter 6: Acids and Bases

Postby goldstanda3269 » Sun Feb 28, 2021 10:15 pm

zimengy17106 wrote:Hi,

I have a question on Q15. I chose C because I thought statement II is not correct?

Statement II: The higher the PH, the greater the activity of carbonic anhydrase. However, carbonic anhydrase is an enzyme so has an optimal PH. If PH too high, the enzyme will be deactivated?

Thanks!


If you have tea at room temperature, and someone says: You will enjoy the tea better if you increase its temperature. I am not sure if you would respond: But there is an optimal temperature, if you increase it too much the tea will evaporate.

Yes, enzymes can denature if the pH is too high. There is clearly a positive correlation between activity and increasing pH for this enzyme. And please remember what the enzyme is doing: deprotonation. This means as the pH goes up, the enzyme keeps working to bring the pH back down so the pH is not going up unchecked. The activity keeps increasing to try and maintain pH balance.
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