Wolfgang Amadeus Mozart's Piano Sonata No. 9 in D major, K 311 (284c) (1777) is a sonata in three movements:
A typical performance takes about 15 to 17 minutes.
The first movement begins with a swift and cheerful melody which lasts for several measures and leads into a passage of rapid sixteenth notes. The section ends with four strong chords, quickly leaping into the second theme (which is repeated). A brief section of the second theme is then repeated in a minor key. With a few soft chords the movement gradually transfers into the swift original melody and closes.
The second movement, being more relaxed, starts with a slow melody accented by soft cadences with the left hand. Gradually the bass progresses with a moving ostinato into the second theme. The main melody is played again, followed by a short minor section. The original key is then reestablished as the second movement ends.
The energetic and robust third movement, being the most technically demanding of the three, begins with several acciaccaturas, and a sixteenth note passage introduces the second theme. The main theme is repeated and enters into a minor section. A rapid chromatic scale takes the piece back to the major key at the conclusion of the sonata. The piece as a whole can be clearly categorized under Mozart's "Middle Period," having matured thematic development and evident orchestral writing.