An alkali metal weighing 15.6 g was dissolved in water. The volume of hydrogen evolved

An alkali metal weighing 15.6 g was dissolved in water. The volume of hydrogen evolved under normal conditions was 4.48 liters. Identify the metal.

Given:
m (Me) = 15.6 g
V (H2) = 4.48 L
To find:
Me =?
Decision:
1) Let’s compose the equation of the chemical reaction, let the molecular weight of the metal be x.
2Ме + 2Н2О = 2МеОН + Н2
2) Vm (H2) = 22.4 L / mol
15.6 g: 2x g / mol = 4.48: 22.4 l / mol
2x = (15.6 x 22.4): 4.48 = 78 g / mol
x = 78: 2 = 39 g / mol
3) The molecular weight of the metal is 39 g / mol, using the periodic table we find that this metal is potassium (K).
Answer: K (potassium).