Question

chlorine gas can be prepared in the lab by the reaction of hydrochloric acid with manganese oxide. you add 42.5g of MnO2 to a solution containing 48.9g of HCL.

A-what is the theoretical yield of Cl2?

B- if the yield of the reaction is 79.5%, what is the actual yield of chlorine?

Answer 1

This is the balanced reaction:

4HCl + MnO2 ----> Cl2 + MnCl2 + 2H2O

You always need the balanced reaction to do calculations of theoretical yield and %yield.

The theoretical yield is the amount of product you expect to obtain with a given amount of reagent. And the %yield is a measure of the amount that you really obtain,

A) First find the limiting reagent:

mol HCl= mass/MW= 48.9g/36.453g/mol= 1.34mol

mol MnO2= 42.5g/87g/mol= 0.49mol

Now if we look at the balanced equation we can see that 4 mol of HCl reacts with 1 mol of MnO2, so, 1.34 mol of HCl will react with 0.335mol of MnO2. We have more MnO2 than we need, so MnO2 is in excess and HCl is the limiting reagent. Now that we know who is the limiting reagent we must do calculations with it.

4 mol of HCl produces 1 mol of Cl2, so, 1.34 mol of HCl produces 1.34/4 mol of Cl2= 0.335 mol.

Now transform mol to mass:

mass of Cl2= 0.335 mol x 70.906g/mol= 23.8g This is the theoretical yield.

B) 79.5%= actual yield/theoretical yield x 100= actual yield/23.8g x100

actual yield= 18.9g