Question

Hydrobromic acid dissolves solid iron according to the following reaction:

Fe(s)+ 2HBr(aq)—> FeBr2(aq) + H2(g)

Question 1:

What mass of HBr (in g) would you need to dissolve a 3.4— g pure iron bar on a padlock?

Question 2:

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

Answer 1

Molar mass of Fe = 55.85 g/mol

mass of Fe = 3.4 g

mol of Fe = (mass)/(molar mass)

= 3.4/55.85

= 0.0609 mol

1)

From balanced chemical reaction, we see that

when 1 mol of Fe reacts, 2 mol of HBr is formed

mol of HBr formed = (2/1)* moles of Fe

= (2/1)*0.0609

= 0.1218 mol

Molar mass of HBr = 1*MM(H) + 1*MM(Br)

= 1*1.008 + 1*79.9

= 80.908 g/mol

mass of HBr = number of mol * molar mass

= 0.1218*80.908

= 9.85 g

Answer: 9.85 g

2)

From balanced chemical reaction, we see that

when 1 mol of Fe reacts, 1 mol of H2 is formed

mol of H2 formed = moles of Fe

= 0.0609 mol

Molar mass of H2 = 2.016 g/mol

mass of H2 = number of mol * molar mass

= 0.0609*2.016

= 0.123 g

Answer: 0.123 g