Working on a quiz and I have no understanding of this. Please help me.

Question

An alkaline battery produces electric energy according to this equation.

 

Zn + 2MnO₂ + H₂O ---> Zn(OH)₂ + Mn₂O₃

 

a. If 30.0 grams of zinc and 45.0 grams of manganese (II) oxide are reacted with excess water, what is the limiting reactant?

b. What mass of zinc hydroxide is produced by the reaction?

I've gotten that Zn is the limiting reactant and that 0.45 grams of Zinc hydroxide would be produced. Am I right, and if not, can someone help me?

Answer 1

No. Unfortunately you are not correct. I will go through the procedure and hopefully it will help you.

Zn + 2MnO₂ + H₂O ---> Zn(OH)₂ + Mn₂O₃ ... balanced equation

Let's find mass of Zn(OH)₂ produced from each reactant as if it were limiting. We will do this by using the stoichiometry (mole ratios) of the balanced equation along with dimensional analysis.

For Zn we have...

30.0 g Zn x 1 mol Zn / 65.4 g Zn x 1 mol Zn(OH)₂/mol Zn x 99.4 g/mol Zn(OH)₂ = 45.6 g Zn(OH)₂

For MnO₂ we have...

45.0 g MnO₂ x 1 mol MnO₂ / 86.9 g x 1 mol Zn(OH)₂ / 2 mol MnO₂ x 99.4 g Zn(OH)₂ /mol = 25.7 g Zn(OH)₂

So, MnO2 is limiting since it produces the lesser amount of product, and that amount would be 25.7 g.