Why are hydrogen-bonded compounds (such as NH3) excellent solvents for most lab reagents?
Recall that hydrogen bonding interactions result from the polarized nature of bonds between hydrogen and nitrogen, oxygen, and fluorine. This polarized bond results in a hydrogen atom with very low electron density—a property that allows the atom to interact very strongly with negatively charged particles.



Thus, anions and electronegative atoms in polarized molecules have very strong electrostatic interactions with the low-electron-density hydrogen atom in $\ce{NH3}$ or $\ce{H2O}$, for example. Cations and positively charged elements in polarized molecules can also be stabilized by the electronegative atoms in molecules exhibiting hydrogen bonding ($\ce{N}$ and $\ce{O}$ in this case).



These strong interparticular interactions ultimately result in polarized or ionic solutes generally being very soluble in solvents with hydrogen bonding such as $\ce{NH3}$ or $\ce{H2O}$.