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Hydrogen bonding exists between $\ce{NH3}$ molecules. When $\ce{NH3}$ is dissolved in water, I know that hydrogen bonds are formed between $\ce{NH3}$ and $\ce{H2O}$ molecules. However, do the $\ce{NH3}$-$\ce{NH3}$ hydrogen bonds still exist?

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It depends on the concentration. For an ammonia concentration of 0.06 mol/L, you would have a thousand water molecules for every ammonia molecule, and the hydrogen bonds between ammonia (if you started with liquid ammonia) will be replaced by ones with water. Also, you will have more hydrogen bonds (ammonia has only one donor, so you can have one hydrogen bond on average per ammonia molecule in pure ammonia). Up to four water molecules can have a direct hydrogen bond with ammonia.

At very high concentrations of ammonia, you would expect occasional direct hydrogen bonds between two ammonia molecules. Because in a liquid, hydrogen bonds are temporary and dynamic, this would eventually be replaced by a hydrogen bond with water, and other pairs of ammonia molecules might form a hydrogen bond.

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    $\begingroup$ Also diluted NH3 is protonated to greater degree. $\endgroup$
    – Mithoron
    Jun 19, 2023 at 17:22

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