To dissolve an iron bar on a padlock, we need to use hydrochloric acid (HCl), which reacts with iron to form iron(II) chloride and hydrogen gas:
Fe + 2HCl -> FeCl2 + H2
The balanced chemical equation tells us that we need 2 moles of HCl for every 1 mole of Fe that reacts.
First, we need to convert the mass of iron into moles:
2.8 g Fe * (1 mol Fe / 55.845 g Fe) = 0.0501 mol Fe
Next, we can use the mole ratio from the balanced equation to determine how many moles of HCl we need:
0.0501 mol Fe * (2 mol HCl / 1 mol Fe) = 0.1002 mol HCl
Finally, we can convert the moles of HCl into grams using the molar mass of HCl:
0.1002 mol HCl * (36.46 g HCl / 1 mol HCl) = 3.65 g HCl
Therefore, we would need a minimum of 3.65 grams of HCl to dissolve a 2.8-gram iron bar on a padlock.