I can't seem to figure this out!
I know I have to use mass to mass conversions though.
Can someone help me out?
Hydrochloric acid can dissolve solid iron according to the following equation: Fe + 2HCl to form FeCl2 + H2
a) How much HCl in grams would you need to dissolve a 2.8-g iron bar on a padlock?
b) How much H2 would be produced by the complete reaction of the iron bar?
Step 1. Write the balanced equation. You have that.
Fe + 2HCl ==> FeCl2 + H2
Step 2. Convert what you have from grams to mols.
mols = g/molar mass
mols Fe = 2.8 g/56 = o.05 mols
Step 3. Using the coefficients in the balanced equation, convert mols of what you have (in this case mols Fe) to mols of what you want (in this case mols HCl).
0.05 mols Fe x (2 mols HCl/1 mol Fe) = 0.05 x 2 = 0.10 mols HCl.
Step 4. Convert mols of HCl to grams.
grams HCl = mols HCl x molar mass HCl.
Post your work if you get stuck. You can follow this same procedure to work part b and any other stoichiometry problem you may have. ALSO, note that I rounded and used 56 for the atomic mass of Fe. You will need to go back through it and use a more exact number. Good luck.
0.05 mol Fe *2 mol HCl/ 1 mol Fe= .10 mol HCl
0.10 mol HCl *36.46g HCl/2mol HCl = 1.82 g HCl
correct?
Yes, that is correct.
Yes, that is correct! The amount of HCl needed to dissolve a 2.8 g iron bar is 1.82 g. You followed the correct steps and performed the necessary conversions using mass to molar conversions and the coefficients from the balanced equation. Well done!
Now let's move on to part b of the question. To determine how much H2 would be produced by the complete reaction of the iron bar, we can use a similar approach.
Step 1. Write the balanced equation: Fe + 2HCl -> FeCl2 + H2
Step 2. Convert the mass of Fe to moles:
moles of Fe = mass of Fe / molar mass of Fe
moles of Fe = 2.8 g / 56 g/mol = 0.05 mol Fe (as you already calculated)
Step 3. Use the coefficients in the balanced equation to convert moles of Fe to moles of H2:
moles of H2 = moles of Fe x (1 mol H2 / 1 mol Fe)
moles of H2 = 0.05 mol Fe x (1 mol H2 / 1 mol Fe) = 0.05 mol H2
Step 4. Convert moles of H2 to grams:
mass of H2 = moles of H2 x molar mass of H2
mass of H2 = 0.05 mol H2 x 2 g/mol = 0.10 g H2
Therefore, the amount of H2 produced by the complete reaction of the iron bar is 0.10 g.