Respiratory acidosis doesn't make sense?

[scilearner]

Hello everyone,

 

C02 + H20 <---> H+ + HCO3-

 

Now in respiratory acidosis. You breathe slowly retaining more carbon dioxide. Ok this would shift the reaction to the right but how does it raise the PH. HCO3- also raised the same amount. Thank you

[Mr Skeptic]

The pH only looks at the H+. It is pH = -log([H+]).

 

Note also that H2CO3 is a weak acid.

[scilearner]

Thanks skeptic. I don't know I have really gone blank and totally confused. So in this solution there are equal amount of base and acid. So how can you just measure the concentration of H+ and say the solution is acidic, don't you have to take account how much base is there in the solution. If there is equal amount of acid and base in a solution shouldn't it be neutral. I know I have some major misunderstanding. Thanks

[Mr Skeptic]

Two ways to think about it. When you put an acid such as H2CO3 in the water it dissociates into H+ and its conjugate base HCO3-. H+ is a strong acid and HCO3- a weaker base, so the H+ counts for more. Another way to think about it is that when you put acid and base into water, they neutralize each other and can't much affect the [H+].

[Belle Richard]

Hello everyone,

 

C02 + H20 <---> H+ + HCO3-

 

Now in respiratory acidosis. You breathe slowly retaining more carbon dioxide. Ok this would shift the reaction to the right but how does it raise the PH. HCO3- also raised the same amount. Thank you

 

Um, I will TRY to answer your question, but don't shoot me if I'm wrong.

 

In respiratory acidosis, as you already know, there is an increase in carbon dioxide. Increased CO2 causes the equilibrium to shift right increasing H2CO3, H+ and HCO3-. Increased H+ ion leads to decreased pH. The HCO3- will then be slightly higher than normal. Now, since the body has its own methods to correct abnormalities in pH, which is referred to as "compensation" methods, and have two main acid-base regulatory mechanisms, then in a case of respiratory acidosis, the kidneys will attempt to compensate for the low pH. The compensation is to increase excretion of H+ ion and therefore increase the retention or re-absorption of HCO3- into the blood. An increase in HCO3- ions in the blood causes the buffer equation to shift left, thus H+ ions decrease and pH increases.

 

Hope this helps.

[cypress]

Thanks skeptic. I don't know I have really gone blank and totally confused. So in this solution there are equal amount of base and acid. So how can you just measure the concentration of H+ and say the solution is acidic, don't you have to take account how much base is there in the solution. If there is equal amount of acid and base in a solution shouldn't it be neutral. I know I have some major misunderstanding. Thanks

 

 

In addition to what the others have said, note that HCO₃^-1 is not an equal base... It is actually a weak acid that further dissociates a bit to provide a bit more H+ as Skeptic indicated. Think of it this way, If it were a base of equal strength to the H+ acid, it would associate all the H+ it could until it was in solution as H₂CO₃.