Final answer:
Ammonia is formed from the bacterial breakdown of urea in a urine sample that has been left unpreserved for over 2 hours.
Step-by-step explanation:
If a urine sample is allowed to sit for over 2 hours unpreserved, ammonia will be formed from the bacterial breakdown of urea. Urea is synthesized in the liver from ammonia which is produced by the oxidation of amino acids. It is a water soluble, non-toxic form that can be safely stored and excreted in urine.
When urine is exposed to bacteria, the urea in it can be broken down back into ammonia, especially if the urine is left unpreserved.