A 0.136 g sample of an unknown metal (X) reacted with excess hydrochloric acid according to the following balanced chemical reaction:
2X(s) + 6 HCl(aq) → 2XCl3(aq) + 3 H2(g)
The volume of hydrogen gas collected over water was 90.5 mL at 20°C and a barometric pressure of 756 mmHg. Determine the atomic mass of the unknown metal. Use the Periodic Table of elements to identify the metal.