Question

Hydrobromic acid dissolves solid iron according to the following reaction:
Fe(s)+2HBr(aq)?FeBr2(aq)+H2(g)

What mass of HBr (in g) would you need to dissolve a 3.0?g pure iron bar on a padlock? Express your answer using two significant figures. m=______________g

What mass of H2 would be produced by the complete reaction of the iron bar?

Express your answer using two significant figures. m=_____________________g

Answer 1

Given is the equation,

Fe(s) + HBr(aq) -------------> FeBr2(aq) + H2(g)

so we can see that,

1 mole of Fe requires 2 moles of HBr

Molar mass of Fe = 55.85 g

Molar mass of HBr = 80.91 g

As 1 mole of Fe requires 2 Mole of HBr

Such that 55.85 g of Fe will use 2 x 80.91 g of HBr= 161.82 g of HBr

thus, 55.85 g of Fe will use 161.82 gms of HBr

and, 1 gms of Fe will need 161.82/55.85 g of HBr = 2.90 g of HBr

Therefore 3.0 g of Fe would need 2.9 x 3.0 g of HBr = 8.70 gms of HBr

Now from the equation we know,

1 mole of Fe produces 1 mole of hydrogen

or, 55.85 g of Fe will produce 2 g of hydrogen

so 1 g of Fe will produce = 2/55.85 g of hydrogen = 0.036 g of hydrogen

given Fe mass = 3.0 g

therefore, 3.0 g of Fe would produce = 3.0 x 0.036 g of hydrogen

                                                               = 0.11 g of hydrogen