Question

$261.6g$ of $Zn$ was burnt in excess of ${O_2} $ to give $244.2g$ of $ZnO$. The percentage yield of$ZnO$ is?
A. $25\% $
B. $50\% $
C. $75\% $
D. None.

Answer 1

Hint: The percentage yield of a reaction is to determine the abundance of an atom in the earth’s crust or atmosphere. This also takes into consideration the isotopes of the element. It is a comparison of the abundance of the different isotopes of the element.

Formula used: $\;percentage\;{{ }}yield = \dfrac{{\exp\; weight}}{{theoretical \;weight}} \times 100$

Complete step by step answer:
It is first required to write the correct balanced reaction using the reactants mentioned.
$Zn + {O_2} \to ZnO$
We now need to find out the amount of substance that would have been produced theoretically. For this we have to remember the atomic mass of the elements and assume that the reaction proceeds to completion that is till the entirety of the reactants is used up.
For this, the mass of $Zn$ is $65g$ and the mass of the product $ZnO$ is $81$ . We will not consider the reactant ${O_2} $ as this is in excess.
Now in the question we know that the concentration of $Zn$ is $261.6g$ and the concentration of $ZnO$ is $244.2g$ .
We know that based on the data given, with $261.6g$ of $Zn$ , the amount of $ZnO$ formed can be found using the method of cross multiplication:
for, $65$ grams of $Zn$ we get, $81$ grams of $ZnO$ .
therefore, for $261.6g$ of $Zn$ we get,

Amount of $ZnO$ theoretically = $\dfrac{{261.6 \times 81}}{{65}}$

$ \Rightarrow 325$
Thus, the percentage yield= \[\dfrac {{244.2}} {{325}} \times 100\]
$\Rightarrow 0.75 \times 100$
$ \Rightarrow 75.1\%$

So, the correct answer is Option c.

Note: The experimental weight is the weight of the product formed when we consider that the reactants will completely disappear and be used up to produce the products.
Theoretical weight is the weight of the product that is mentioned in the question.
By comparing these two the value of percentage yield is calculated.