Question

Calcium hydride reacts with water to form calcium hydroxide and hydrogen gas. The balanced equation for this is CaH2 + 2H2O ---> Ca(OH)2 + 2H2 (a) How many grams of calcium hydride are needed to form 4.500 g of hydrogen?

Answer 1

If 4.5 g of Hydrogen is to be formed then this mass would have in x mol

x mol = Mass of H ÷  Molar Mass of H
         =  4.5g ÷ ( 1 x 2) g/mol
         = 2.25 mol

mole ratio of  CaH₂  :  H₂
                          1    :   2

∴ if mol of H₂ = 2.25 mol

then mol of CaH₂ = 2.25 mol × $\frac{1}{2}$
     
                             =  1.125 mol

Mass of CaH₂  =  1.125 mol  ×  [(40 × 1) + (2 × 1)]
                        =  47.25 g

Answer 2

I believe the answer is 47.25g
let me know if you need the workings i'll try and put it up