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Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: Bakda on August 18, 2021, 01:17:52 PM

Title: Urea measurements in water
Post by: Bakda on August 18, 2021, 01:17:52 PM
Hello,
Biology/chemistry question. I am confused.

You can purchase powder urea, (CO(NH2)2).

If you add this to water (H2O), you apparently get carbondioxide (CO2) and ammonia (NH3).

Urea is an animal and fish and waste product.
People take urea measurements in lakes, rivers, oceans, and sewage processing plants. How is this possible? If urea is immediately converted to carbon dioxide and ammonia in water, how could the urea concentration in water be anything but absolute 0?

They do not just test for ammonia, because that is a separate reading/measurement.
Title: Re: Urea measurements in water
Post by: Borek on August 18, 2021, 01:30:19 PM
immediately converted

Not immediately. Slowly enough.
Title: Re: Urea measurements in water
Post by: Bakda on August 18, 2021, 01:41:52 PM
immediately converted

Not immediately. Slowly enough.

Is that really it?
Any idea how I could calculate the rate?

For example if i added 1g urea to 100ml of water, how long would it take for there to be no urea? How would I know?
Title: Re: Urea measurements in water
Post by: Bakda on August 18, 2021, 03:08:31 PM
Actually, after some more research, it seems like there is a lot of misinformation.
I have seen many posts that say that urea in h2o remains urea…
Title: Re: Urea measurements in water
Post by: Orcio_Dojek on August 18, 2021, 03:14:31 PM
Hydrolysis of (H2N)2CO is the pseudo-first reaction order and I found that "urea is stable in aqueous solutions between pH 2 and 12, with a half-life of 3.6 years at 38°C (Zerner, 1991)". [K. A. Fisher, University of Maryland, 2014].
Title: Re: Urea measurements in water
Post by: Babcock_Hall on August 18, 2021, 06:49:51 PM
8 M aqueous urea is in equilibrium with around 20 mM each ammonium ions and cyanate ions IIRC.  I believe that the kinetics are slow, inasmuch as one can clean up concentrated urea solutions using mixed-bed ion exchange resins and store the solution in the freezer.