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 2.8-g pure iron bar on a padlock?
What mass of H2 would be produced by the complete reaction of the iron bar?

8.1g

0.1g

Explanation:

The reaction expression is given as:

      Fe   +   2HBr   →  FeBr₂    +    H₂

Mass of pure iron given  = 2.8g

A. Mass of HBr needed to dissolve a padlock of the mass;

To solve this problem, we need to use the mole concept.

 Convert mass of the known iron to the number of moles.

  Number of moles =  

  Molar mass  = 56g/mol  

   Number of moles of iron  =   = 0.05mole

 1 mole of Fe will react with 2 mole of HBr

 0.05mole of Fe will react with 0.05 x 2  = 0.1mole of HBr

 Mass of HBr  = number of moles x molar mass

   Molar mass of HBr  = 1 + 80   =  81g/mol

 Mass of HBr  = 0.1 x 81  = 8.1g

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

    Since:

         1 mole of Fe will produce 2 mole of hydrogen gas

        0.05mole of Fe will produce 2 x 0.05mole  = 0.1mole of hydrogen gas

 Mass of hydrogen gas  = number of moles x molar mass

                                          = 0.1 x 1

                                          = 0.1g

b is the correct answer

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