Question

An impure sample of $CaC{O_3}$ contains $38\%$ of $Ca$. The percentage of impurity present in the sample is?

Answer 1

This question gives the knowledge about the molecular formula and weight of the chemical compounds. The molecular formula is the representation of chemical compounds. It comprises the chemical symbols for the elements tailed by the numeric subscripts labelling the atoms of each element present in a molecule.

Complete step-by-step answer: The molecular formula is the way of representing the chemical compounds. It comprises the chemical symbols for the elements tailed by the numeric subscripts labelling the atoms of each element present in a molecule.
Impurities are defined as the chemical substances present in a very small amount inside the chemical species differing in the chemical composition of the compound.
Firstly, to determine the percentage impurity in the sample we have to calculate the $Ca$ present in the $CaC{O_3}$ .
$\Rightarrow \% Ca = \dfrac{{{M_{Ca}}}}{{{M_{CaC{O_3}}}}} \times 100$
Where ${M_{Ca}}$ is the molecular weight of calcium $Ca$ and ${M_{CaC{O_3}}}$ is the molecular weight of calcium carbonate.
The molecular weight of calcium is $40$ and the molecular weight of calcium carbonate is $100$. Substitute these values in the chemical formula to determine the $\% Ca$ present in the impure sample:
$\Rightarrow \% Ca = \dfrac{{40}}{{100}} \times 100$
The amount of calcium present in the calcium carbonate is
$\Rightarrow \% Ca = 40$
The percentage of calcium given in the impure sample is $38\%$.
The change in impurity is determined by the difference between the given percentage $\left( {38\% } \right)$and the calculated percentage $\left( {40\% } \right)$,
$\Rightarrow 40 - 38$
Therefore, the change is
$\Rightarrow 2$
The percentage of impurity present in the sample is determined as follows:
$\Rightarrow \% {\rm I} = \dfrac{C}{{{M_{Ca}}}} \times 100$
Where $I$ is the impurity, $C$ is the change in impure sample and ${M_{Ca}}$ is the molecular weight of calcium $Ca$ . Substitute all the values,
$\Rightarrow \% {\rm I} = \dfrac{2}{{40}} \times 100$
So, the percentage of impurity present in the sample is
$\Rightarrow \% {\rm I} = 5$
Therefore, the percentage of impurity present in the sample is $5$.

Note: You should have the complete knowledge about the molecular formulas of the chemical compounds. And also always remember the molecular weights of chemical compounds. Impurities are substances present in a very small amount inside the chemical species differing in the chemical composition of the compound.