What happens when urine is allowed to stand for sometime exposed air?

When human urine is allowed to stand for some time exposed to the air, several changes occur due to the presence of ureas and uric acid.

Here's what happens:

1. Breakdown of Urea: Urea, a major component of urine, undergoes enzymatic hydrolysis by the ureas present in bacteria commonly found in the environment. When ureas react with water, they catalyze the breakdown of urea into ammonia (NH3) and carbon dioxide (CO2).

2. Alkalinization: As ammonia is released, it raises the pH of the urine, making it more alkaline. This rise in pH can be noticed by a change in the color of urine, shifting towards a darker yellow or even a brownish hue.

3. Putrid Odor: The production of ammonia results in a pungent and unpleasant odor. Ammonia has a distinct sharp smell that can be detected as the concentration increases.

4. Formation of Ammonium Salts: The ammonia produced can combine with other compounds in urine, such as phosphates and carbonates, to form ammonium salts. These salts contribute to the cloudiness or turbidity of the urine.

5. Microbial Growth: The alkaline environment and presence of organic compounds serve as a favorable condition for microbial growth. Various types of bacteria and fungi can thrive in urine, leading to the decomposition and eventual putrefaction of its constituents.

6. Color Changes: As urine decomposes, it can undergo further chemical changes, resulting in the formation of various pigments and colored compounds. These compounds can give urine a yellowish-brown, reddish, or even purple color.

It's worth noting that the exact changes and the rate at which they occur depend on several factors, including temperature, humidity, the initial concentration of urea and uric acid, and the specific microbial species present in the environment.