# chem

posted by on .

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?

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