Biology pH questions

[Spitphire]

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Not really a MCAT question, but it may be a good refresher and i have a biology test tomorrow so i need help understanding these questions

1.) H2CO3 ---> HCO3-(negative) + H+

If the pH of blood increases, one would expect

A.) A decrease in the concentration of H2CO3 and an increase in the concentration of HCO3-
B.) A increase in the concentration of H2CO3 and an decrease in the concentration of HCO3-
C.) A decrease in the concentration of HCO3- and an increase in the concentration of H+
D.) A increase in the concentration of HCO3- and an decrease in the concentration of OH-

Correct answer is A, but im not sure why.


2.) A give solution contains 0.0001(10^-4) moles of hydrogen ions [H+] per liter. Which of the following best describes this solution?
A.) Acidic: will accept H+ from both strong and weak acids.
B.) Basic: will accept H+ from both strong and weak acids.
C.) Acidic: will give H+ to weak acids, but accept H+ from strong acids.
D.) Basic: will give H+ to weak acids, but accept H+ from strong acids.


Correct answer is C. I know it's acidic, but im not sure why it can give to weak and receive from strong acids. Any help would be appreciated!

(this is NOT a homework question btw, this was on a previous quiz that has already been graded.)

 

[Jkh389]

For 1, it's just a general equilibrium reaction. When pH increases, it means H+ decreases. So how does Le Chatliers principle work in this situation? Well, it shifts to the right to produce more bicarbonate and hydrogen ion, while, reducing carbonic acid.

For 2, the pH of the solution is 4. If you have a strong acid it will react by receiving a H+ because the pH of strong acids are usually less than 2. A weak acid can have a pH range from 2-7, depending on its specific pKa and concentration. So it is reasonable to assume a weak acid will receive a H+ if the pH is higher than the solution because it will in essence be acting as a bronsted base.

 

[Spitphire]

For 1, it's just a general equilibrium reaction. When pH increases, it means H+ decreases. So how does Le Chatliers principle work in this situation? Well, it shifts to the right to produce more bicarbonate and hydrogen ion, while, reducing carbonic acid.

For 2, the pH of the solution is 4. If you have a strong acid it will react by receiving a H+ because the pH of strong acids are usually less than 2. A weak acid can have a pH range from 2-7, depending on its specific pKa and concentration. So it is reasonable to assume a weak acid will receive a H+ if the pH is higher than the solution because it will in essence be acting as a bronsted base.

That makes perfect sense now 😀 The second one I guess i did know but i wasn't entirely sure thank you!

 

[Jkh389]

No problem. For the carbonic acid, you'll want to understand it more in-depth because it shows up in the circulatory system review for biology in most review materials. Try to remember that increases in CO2 concentrations lead to increases in H+, or that it lowers pH. This simple relationship can help you solve many of the Review questions that ask you what happens when pH changes or when CO2 changes!

 

[Spitphire]

No problem. For the carbonic acid, you'll want to understand it more in-depth because it shows up in the circulatory system review for biology in most review materials. Try to remember that increases in CO2 concentrations lead to increases in H+, or that it lowers pH. This simple relationship can help you solve many of the Review questions that ask you what happens when pH changes or when CO2 changes!

That was actually one of the questions on my test yesterday
it was like "if you increase the amount of CO2 in blood what happens?"
Choices were: the pH would slightly increase, the pH would stay the same, or the pH would increase, then decrease because it'll do something with hemoglobin? I picked the last one, not really sure which was right

I just thought of the question as the body will try to compensate for the increase of CO2 so it'll try to do something to regulate the pH so i chose the last choice, not sure though