Textbook problem 6.19

[Joanne Sarsam 2F]

Hi,

The problem states: Hemoglobin (Hb) molecules in blood carry O2 molecules from the lungs, where the concentration of oxygen is high, to
the tissues where it is low (see the Interlude following Focus 5). In the tissues the equilibrium H3O+(aq) 1 HbO2- (aq) <--> HHb(aq) + H2O(l) + O2(aq) releases oxygen. When muscles work hard, they produce lactic acid as a byproduct. (a) What effect will the lactic acid have on the concentration of HbO2-? (b) When the hemoglobin returns to the lungs, where oxygen concentration is high, how does the concentration of HbO2- change?


I understand the answer to part b is because the Hb molecules will combine with the O2- to make more HbO2-, increasing it's concentration. However, could someone please explain the solution to part a to me, as its a little more confusing. Thank you so much!

[Sydney Ngao 3I]

I'm not sure if this is correct, but here is what I'm thinking.. I think that the HbO2- concentration would be lower when there is more lactic acid present, because the muscles were working and using up the oxygen that it carries. Lactic acid is being produced when the muscles are working, so HbO2- would need to release the oxygen so the muscles can function properly and HbO2- would decrease as it releases the oxygen.

[Rose Arcallana 2B]

For A. I thought of it like Le Chatelier. Lactic acid will act as the H3O+ and since HbO2- is on the same reactant side, increasing H3O+ will induce a decrease of HbO2- to keep the reaction in equilibrium, not sure if that's the right process of thinking though. Another way would be increasing H3O+ will produce more HHb, therefore more HbO2- will be used lowering its concentration. Hope it helps!

[Divya Hebbar]

more lactic acid will increase the H3O+ concentration because it is an acid and will give off protons. This shifts the reaction to the products side increasing the O2 production.