Problem 1
Nitrogen trifluoride is a surprisingly stable compound that was first prepared by the melt electrolysis of a mixture of ammonium fluoride and hydrogen fluoride. (a) At which electrode does form? Write the balanced half-reaction for its formation. (b) The related compounds and are very unstable and form as side products. Which of , , is expected to condense at the lowest temperature? (c) The N–F bond lengths in these molecules are 136, 140 and 142 pm; assign them using a simple electrostatic (partial-charge) model. (d) When is bubbled through a solution of KF in HF, a binary nitrogen–fluorine compound is obtained as a mixture of two geometric isomers; write a balanced equation for its formation. (e) salts form from and in the presence of a suitable reagent — propose one and write the equation. (f) hydrolyzes to and , but less than expected is often obtained; write the hydrolysis equation and a possible side reaction lowering the : ratio. (g) A tetrafluoroammonium salt (a candidate solid rocket fuel) contains 65.6% fluorine by mass, all released as and on heating, with . Determine the formula of the salt.
Step 2 of 6: Boiling point and bond-length assignment
Analysis
has no N–H bonds, so no hydrogen bonding — it condenses at the lowest temperature. Each F on nitrogen pulls electron density toward itself and away from the remaining bonds: the more F atoms, the shorter the N–F bonds, hence 142 pm, 140 pm, 136 pm.