Question

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

Part A:

What mass of HBr (in g) would you need to dissolve a 2.6 −g pure iron bar on a padlock?

Express your answer using two significant figures.

Part B:

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

Express your answer using two significant figures.

Answer 1

A)

Molar mass of Fe = 55.85 g/mol

mass of Fe = 2.6 g

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

= 2.6/55.85

= 4.655*10^-2 mol

According to balanced equation

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

= (2/1)*4.655*10^-2

= 9.311*10^-2 mol

Molar mass of HBr,

MM = 1*MM(H) + 1*MM(Br)

= 1*1.008 + 1*79.9

= 80.908 g/mol

mass of HBr = number of mol * molar mass

= 9.311*10^-2*80.91

= 7.533 g

Answer: 7.5 g

2)

According to balanced equation

mol of H2 formed = moles of Fe

= 4.655*10^-2 mol

Molar mass of H2 = 2.016 g/mol

mass of H2 = number of mol * molar mass

= 4.655*10^-2*2.016

= 9.385*10^-2 g

Answer: 9.4*10^-2 g