The physiological mechanism for renal tubule exchange of ammonia (NH3 + NH4+) between the blood and the urine is illustrated in the figure above. The equilibrium dissociation reaction for ionized ammonia is written as NH4+ ↔ NH3 + H+ and is defined by the equilibrium dissociation constant:
Kdn = [NH3]*[H+]/[NH4+] = 10^(-9.25)

Determine the CU/CB ratio for the total ammonia concentration in urine, CU – where CU = [NH3]U + [NH4+]U – divided by the total ammonia concentration in blood, CB – where CB = [NH3]B + [NH4+]B

In formulating your answer, make the following assumption:
1) Only unionized ammonia (NH3) freely diffuses across the membranes separating blood from urine;
2) Only unionized ammonia (NH3) is in equilibrium between both sides of the membranes separating blood from urine such that [NH3]U = [NH3]B
Explain and justify
CU/CB = ?