Was The burning of Washington Dc by the British an attempt to boost American morale?

No, the British did not burn down Washington D.C. in an attempt to boost American morale. In August of 1814, the British did burn down Washington D.C. but this was after the signing of the Treaty of Ghent, which officially ended the War of 1812. The burning of Washington D.C. was done as retaliation for American attacks on Canada and the capture of York, Ontario.