Sapling HW Question 13

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Nayra Gharpetian 3F
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Sapling HW Question 13

Postby Nayra Gharpetian 3F » Thu Nov 12, 2020 9:22 pm

Hi can someone explain how to do this problem? I can't seem to get the correct answer.

Urea is an organic compound widely used as a fertilizer. Its solubility in water allows it to be made into aqueous fertilizer solutions and applied to crops in a spray.
What is the maximum theoretical number of water molecules that one urea molecule can hydrogen bond with? Ignore shape for the purposes of this answer.

Marcus Lagman 2A
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Re: Sapling HW Question 13

Postby Marcus Lagman 2A » Thu Nov 12, 2020 9:47 pm


To answer this question, we must know what a hydrogen bond is and when it forms.

So from what Professor Lavelle taught us, a hydrogen bond is a special type of dipole-dipole bond that occurs between two highly electronegative atoms; one of them has to be a hydrogen atom covalently bonded to either an Oxygen, Nitrogen or Fluorine atom. So from this definition, we can solve the problem:

On the organic compound, Urea, there are many highly electronegative atoms and Hydrogen atoms that are covalently bonded to Nitrogen atoms. Since water molecules are highly electronegative due to their distinct positive Hydrogens and negative Oxygen dipoles, the water molecules can theoretically form 8 hydrogen bonds at 8 sites of Urea: the four Hydrogen atoms attached to Nitrogen, the lone pair of each of the two Nitrogen atoms, and the two lone pairs of the Oxygen atom.

I hope this helps!

Angel More
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Re: Sapling HW Question 13

Postby Angel More » Thu Nov 12, 2020 9:52 pm

We know that a hydrogen bond forms when there is a hydrogen bonded to two very electronegative molecules. Both a nitrogen atom and oxygen atom, with an unshared pair of electrons, can form a hydrogen bond by bonding to a hydrogen (of a water molecule). Also, if a Hydrogen is already bonded to nitrogen, then it can bond to the Oxygen (of a water molecule).

Urea has 1 oxygen, 2 nitrogen, and 4 Hydrogens bonded to nitrogen.

Since the oxygen in Urea has 2 unshared pairs of electrons it can bond with 2 hydrogens. The 2 nitrogen can each bond with a hydrogen, and each of the 4 Hydrogens bonded to nitrogen can bond with an oxygen.

Thus, Urea can form hydrogen bonds with eight water molecules.

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Re: Sapling HW Question 13

Postby Reese_Gover2K » Sat Nov 14, 2020 5:42 pm

So since a Hydrogen bond occurs between Hydrogen and N, O, and F we can look for these atoms in the molecule. Since Oxygen has 2 lone pairs meaning that it can form 2 Hydrogen bonds, and there are 2 Nitrogens each with 1 lone pair that is 2 Hydrogen bonds, and lastly there are 4 Hydrogen atoms that can form 4 Hydrogen bonds. If youa dd all these up you get 8 Hydrogen bonds! Hope this helps :)

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