Calculate the volume, amount of substance and mass of gas obtained by the interaction of 3.5 g of lithium with water.

Given:
m (Li) = 3.5 g
To find:
m (H2) =?
V (H2) =?
new (H2) =?
Decision:
1) Let’s compose the equation of the chemical reaction
2Li + 2H2O = 2LiOH + H2
2) Find the mass of the gas, that is, hydrogen. For this, we calculate the molecular weights of Li and H2
M (Li) = 7 g / mol, since 2 molecules are 14 g / mol
M (H2) = 1 x 2 = 2 g / mol
Let the mass of H2 be x g, then 3.5 g: 14 g / mol = x g: 2 g / mol
x = (3.5 x 2): 14 = 0.5 g
3) New = m: M
New (H2) = 0.5: 2 = 0.25 mol
3) To find the volume of hydrogen, let H2 be x l. Vm (H2) = 22.4 L / mol
3.5 g: 14 g / mol = x L: 22.4 L / mol
x = (3.5 x 22.4): 14 = 5.6 l
Answer: m (H2) = 0.5 g; V (H2) = 5.6 L; new (H2) = 0.25 mol.