Help Please!! Bio/Chem Question!

[ckmonster]

This is from one of my exams when I took Bio!



The answer is A, I dont understand why! 🙁 Can someone explain it to me!



One of the buffers that contribute to pH stability in human blood is carbonic acid H2CO3. Carbonic acid is a weak acid that when placed in an aqueous solution dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). Thus,

H2CO3 .⇔. HCO3- + H+​

​

If the pH of the blood increases, one would expect
A) a decrease in the concentration of H2CO3 and an increase in the concentration of H2O.
B) an increase in the concentration of H2CO3 and a decrease in the concentration of H2O.
C) a decrease in the concentration of HCO3- and an increase in the concentration of H2O.
D) an increase in the concentration of HCO3- and a decrease in the concentration of H2O.
E) a decrease in the concentration of HCO3- and an increase in the concentration of both H2CO3 and H2O.

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[dfymarine]

This is from one of my exams when I took Bio!



The answer is A, I dont understand why! 🙁 Can someone explain it to me!



One of the buffers that contribute to pH stability in human blood is carbonic acid H2CO3. Carbonic acid is a weak acid that when placed in an aqueous solution dissociates into a bicarbonate ion (HCO3-) and a hydrogen ion (H+). Thus,

H2CO3 .⇔. HCO3- + H+​

If the pH of the blood increases, one would expect
A) a decrease in the concentration of H2CO3 and an increase in the concentration of H2O.
B) an increase in the concentration of H2CO3 and a decrease in the concentration of H2O.
C) a decrease in the concentration of HCO3- and an increase in the concentration of H2O.
D) an increase in the concentration of HCO3- and a decrease in the concentration of H2O.
E) a decrease in the concentration of HCO3- and an increase in the concentration of both H2CO3 and H2O.

okay, try to think of le chatelier's rule, so by increasing the pH, you are going to increase the concentration of [OH-] and decrease the concentration of [H+], right?

so, the shift favors the product over the reactant, which means it is shifting to the right side. Thus, the concentration of H2CO3 decreases, whereas the concentration of H2o is increased.

 

[ckmonster]

OMG! I feel like punching myself in the face! This is so easy! I was doing Le Chantelier's but thinking about it the other way around!

Appreciate your help! 🙂

 

[Shinpe]

okay, try to think of le chatelier's rule, so by increasing the pH, you are going to increase the concentration of [OH-] and decrease the concentration of [H+], right?

so, the shift favors the product over the reactant, which means it is shifting to the right side. Thus, the concentration of H2CO3 decreases, whereas the concentration of H2o is increased.

I agree with the H2CO3 decreasing part, but I'm not sure with the way they say water is changing. Two reactions that could affect it are:
H20+CO2 -> H2CO3
H2O - > H+ + OH-

In both cases, lowering of H+ results in removal of products so the rxn should shift to right, which would mean decrease H2O, right? What am I missing?

 

[orangutan777]

the H is coming from when H2CO3 -> H + HCO3 not from splitting of water