How many grams of metallic Na will be needed to produce 25.43 grams of H2 upon reaction with H2O?

Question

I need help setting up the equation.

Answer 1

Stoichiometry

Write the correctly balanced equation:

2Na(s) + 2H₂O(l) ==> 2NaOH(aq) + H₂(g) ... balanced equation

Convert grams H₂ to moles H₂:

25.43 g H₂ x 1 mol H₂/2.016 g = 12.61 moles H₂

Using the balanced equation and dimensional analysis, to find moles of Na needed:

12.61 mol H₂ x 2 mol Na / 1 mol H₂ = 25.23 moles Na needed

Convert moles Na to grams Na:

25.23 moles Na x 22.99 g/mol = 579.995 g Na = 580.0 g (to 4 significant figures)

If you want to string the entire calculation into one equation, it would look like this:

25.43g H2 x 1 mol H2/2.016g x 2 mol Na/mol H2 x 22.99 g Na/mol = 579.995 g Na = 580.0 g Na