In the third movement of Mozart's Piano Sonata in C Major K. 545, he introduces a new harmonic color by placing a Neapolitan augmented sixth in measure 47. Before this, however, the chord analysis from measure 41 is as follows:
m. 41: i64
m. 42: V
m. 43: i6
m. 44: V64, v6
m. 45: ii half diminished42, III
m. 46: iv
m. 47: Neapolitan +6, V
m. 48: i
Therefore, the N+6 is approached by a iv chord. This means that the solfege syllable me is going down to the ra of the N+6 chord. This is rather typical for the voice leading into a N+6 chord. However, the N+6 chord is left in an unusual way. Typically, the ra of the chord will resolve to the ti of the next chord. This does not happen immediately, however. There is a ti that shows up in the last eighth note of the measure, and this is expected. The ti is the last note of the melody line, the G#.
It seems that this Neapolitan sixth is not used in the typical way that other composers might choose to use it. In many cases, it seems that the texture when using this type of chord is thicker than in the Mozart; the use of a thicker texture causes an extreme sense of angst or urgency that does not seem present in this piano sonata. Perhaps Mozart only used it to provide a bit of contrast to the rest of the movement. It also serves as a nice lead-in to the cadence of measures 47-48, seeing as a typical N+6 progression is N+6-V-i. This is also typical because they are often used at the last cadence of a piece, and though this is not the cadence of the piece, it is a cadence within a movement. Truly, Mozart displays his adaptability and inventiveness while using this unique chord.