Earlier, in the second line of the piano song, we encountered a scale phrase that went up and down again continuously. The fingers never lost contact with the keyboard while playing it.
Now in the 1st bar of the 11th line of the piano song, a series of scale phrases take their turn to adorn the piece. Unlike the phrase we played earlier, this time they are not continuous.
Instead, the first of the series of the scales starts in the treble clef with a D that ascends an octave to the next D and stops. Previously the phrase would have descended, but not here.
On this occasion the RH rests while LH plays a scale in the bass clef starting with the second note of the bar, an F that descends one octave until G#.
Then it is the LH’s turn to rest while the RH plays a scale beginning with a B ascending one octave until the next B. The pattern is repeated for several bars to create what resembles a musical conversation between the RH and LH. The RH speaks scales that ascend while the LH answers with scales that descend.
When observing the rests in the treble clef, raise your RH high while the LH does its work. Just as the LH is about to finish, lower the RH slowly, time its drop so that it lands on the key at exactly the moment after the last note of the scale in the bass clef has been struck and the finger pressing it has lifted off it.
Similarly, do so with the LH as well. Can you picture it? The arms dancing above the keys, as the RH hovers just for a few seconds while the LH plays, then their positions are reversed, taking turns to dance on the piano and rising away from it.
The chats between the LH and RH continue into the 3rd bar of line 12 of the piano song. In the bar that follows, the LH returns to its role of accompanying the melody in the treble clef, made to sing by the orchestrated strikes of the RH fingers.
Play the first note D in bass clef first before you start the phrase in the treble clef, they do not begin simultenously - look out for the semiquaver rest at the top of the bar in the treble clef.
Observe this rest, then hit the B flat with the middle finger. Open your RH a bit so that you shall be able to reach D with the 5th finger that comes next, and move down the keyboard all the way to E to perform a scale descent.
As the scale descends, prepare the LH to play a triple note chord – specifically, get the LH’s fingers 5,2 and 1 ready to land on C, G and B flat in harmony. They make their debut when the scale phrase in the treble clef lands on the last note, E, in its downward voyage.
Hold the chords longer as they are minims, while the thumb in the RH moves under the index finger that had just struck the E to play F and send the scale phrase up the keyboard to ascend until the next E , an octave higher. During the climb, use the 4th finger to play the B flat, then thumb-under it to continue the ascent until E.
The climb does not end there, after the E is played with the 3rd finger, guide your thumb under the middle finger to extend the ascent of the scale phrase into the next bar by ending it on a minim F.
The minim F fulfills a dual role of completing the ascending scale phrase and initiating the next movement in this piano song. It is the first note of the second movement of Sonata K545 that plays in a similar rhythm as the previous one albeit in a minor key.
Since only the notes in the melody and accompaniment are different, and by this time you should have known the rhythm by heart, it would be easy to adapt to playing this part of the piano song.