FeCl3 + 3NH4OH → Fe(OH)3 + 3NH4Cl

Question

If 6.4 moles of ammonium chloride are produced, how many moles of iron(III) chloride reacted? Remember to write your answer with the correct number of significant digits. No units are necessary for this question .

Answer 1

The equation for this reaction is balanced. It tells us that 3 moles of ammonium chloride are produced from 1 mole of iron(III) chloride, a 3/1 molar ratio of NH₄Cl/FeCl₃. We can use this as a conversion factor.

(6.4 moles NH₄Cl) is divided by 3NH₄Cl/1FeCl₃ to yield (1/3)*(6.4) moles FeCl₃ or 2.1 moles FeCl₃, to 2 sig figs.

Note: I dislike division since it is both harder to see the written equation: (6.4 moles NH₄Cl)/(3NH₄Cl/1FeCl₃),

and because it is more difficult predicting the answer (for me).

Since the 3/1 molar ratio is a conversion factor, we can simply invert it to: (1 FeCl₃/3NH₄Cl) and then multiply:

(6.4 moles NH₄Cl)*((1 FeCl₃/3NH₄Cl) = 2.1 moles FeCl₃.