posted by Anne on .
a 2.00 g sample of zinc was dissolved in 50.0 mL of 6.0 M HCL the final volume of solution was 50.2 mL...
a. what was the concentration of Cl- after the zinc was dissolved??
b. what was the concentration of hydrogen ion after the zinc was dissolved??
a. Chloride comes ONLY from HCl and none was used; therefore, mols Cl^- = M x L = ? and M = mols/L. That's 6.0 x 0.0500 for mols Cl^- and that/0.0502 for new M.
Zn + 2HCl ==> ZnCl2 + H2
This is a limiting reagent problem with others all rolled into one. First determine the limiting reagent.
Convert 2.00 g Zn to mol. mol = grams/atomic mass.
Convert HCl to mols = M x L = ?
Use the coefficients in the balanced equation to convert mols Zn to mols H2.
Do the same for mols HCl.
It is likely you will get different numbers for mols H2; therefore, one of them must be wrong. The correct value in limiting reagent problems is ALWAYS the smaller one and the reagent producing that number is the limiting reagent. I think Zn is limiting.
Second part of the question:
Convert mols Zn to mols HCl. This gives mols HCl used.
mols HCl unreacted = initial mols - mols used.
mols (H^+) = mols HCl unreacted/L and L in this is 0.0502 since that's the final volume in the problem.