Question

How many grams of potassium chloride are produced if 25.0g of potassium chlorate decompose?

Answer 1

Hint In potassium chlorate molecule there is one K atom,one Cl atom and three O atom present. The equation to find the number of moles of the substance is given as,
$\text{no}\text{. of moles=}\dfrac{\text{Given mass of the substance}}{\text{Molecular mass of the substance}}$

Complete step by step solution:
So in the question, it is given that by the decomposition reaction of 25g of potassium chlorate, how many grams of potassium chloride will be produced.
Before going into the solution part let’s have some basic idea of the decomposition reaction. We are familiar with many types of reactions and among them is the decomposition reaction. In a decomposition reaction the compound gets decomposed to simpler compounds. Generally the decomposition reaction requires any external source to initiate the decomposition reaction. The external aids like heat, light, electricity etc.
Here we are considering the decomposition reaction of potassium chlorate.
Potassium chlorate has the molecular formulae $\text{KCl}{{\text{O}}_{\text{3}}}$and it’s getting decomposed into potassium chloride which has molecular formulae of $\text{KCl}$.
So first let’s write the decomposition of $\text{KCl}{{\text{O}}_{\text{3}}}$
$2KCl{{O}_{3}}\to 2KCl+3{{O}_{2}}$
Now we have to find the number of moles of $\text{KCl}{{\text{O}}_{\text{3}}}$in 25g of the sample given.
To find the number of moles of the substance which is of concern, we use the equation,
$\text{no}\text{. of moles=}\dfrac{\text{Given mass of the substance}}{\text{Molecular mass of the substance}}$
Here we, the given mass of $\text{KCl}{{\text{O}}_{\text{3}}}\text{=25g}$
Now we have to calculate the molecular mass of $\text{KCl}{{\text{O}}_{\text{3}}}$
The atomic mass of K is 39, Cl is 35.5 and O is 16
$\text{Molecular mass of KCl}{{\text{O}}_{\text{3}}}\text{=39+35}\text{.5+3 }\!\!\times\!\!\text{ }\left( \text{16} \right)\text{=122}\text{.5g/mol}$
Therefore we will find the number of moles as per the equation,
$\text{no}\text{. of moles=}\dfrac{\text{25}}{\text{122}\text{.5}}\text{=0}\text{.2040mol}$
Now if we consider the chemical equation we know that the mole ratio of $\text{KCl}{{\text{O}}_{\text{3}}}$ and $\text{KCl}$ is 1:1
Therefore lets calculate the weight of $\text{KCl}$when 25g of $\text{KCl}{{\text{O}}_{\text{3}}}$ is decomposed.
No.of moles of $\text{KCl}$ is 0.2040mol
We alter the equation of number of moles and write the equation for weight of the substance.
$\text{no}\text{. of moles=}\dfrac{\text{Given mass of the substance}}{\text{Molecular mass of the substance}}$
$\text{Weight of the substance=no}\text{. of moles }\!\!\times\!\!\text{ molecular}\,\text{mass}\,\text{of substance}$
$\text{Weight of the substance=0}\text{.2040 }\!\!\times\!\!\text{ 74}\text{.5=15}\text{.198g}$
And we got the final solution of the question,the weight of $\text{KCl}$ formed is 15.198g.

Note: Always write the balanced chemical equation for these types of questions, so that we will be able to calculate the mole ratio between the compounds formed in the chemical reaction by comparing the respective coefficients of the atoms.
The unit of number of moles of the substance is mol.
The unit of weight of the sample is grams.