The Piano Sonata in B-flat major, K. 498a (Anh. 136), is a piano sonata in four movements. It was first printed in 1798 by P. J. Thonus in Leipzig on behalf of Breitkopf & Härtel and attributed to Wolfgang Amadeus Mozart; an edition printed in c. 1805 already credited it as opus 26 of the Thomascantor August Eberhard Müller (1767–1817).^[1] Some publications still attribute it to Mozart, often as Piano Sonata No. 20.^[2]

Form

A typical performance lasts for about 19 minutes. The movements are:

The musicologist Alfred Einstein suggested that the Menuetto from this work might be a piano arrangement of the "missing movement" of Mozart's Eine kleine Nachtmusik, K. 525 (1787).^[3]

The Andante is an arrangement of the variations movement of the concerto K. 450 in B-flat major, and the Rondo incorporates arrangements of passages from the finales of the B-flat concerti K. 450, K. 456, and K. 595.

Recordings

• Vincenzo Balzani: Pagine rare per pianoforte / Wolfgango Amadeo Mozart (1980), Ducale CD 349/350^[4]
• Transcription for chamber string orchestra recorded by the Hanover Band, Nimbus CD NI5228