Question

In an experiment, $1.0g$ $CaC{{O}_{3}}$ on heating evolved $224ml$ of $C{{O}_{2}}$ at NTP. What mass of $CaO$ (calcium oxide) is formed?
A.$0.56$
B.$56$
C.$0.57$
D.$0.58$

Answer 1

Hint: Mole concept gives the relationship between the number of moles, weight and molar mass of the compound. Molar mass is calculated by adding up the atomic masses of the element combined to form a molecule.

Formula used:
$n=\dfrac{W}{M}$
Where, $n$ is the number of moles, $W$ is the weight of the compound and $M$ is the molar mass of the compound. 
Complete step-by-step answer: In this question, it is given that the moles of $CaC{{O}_{3}}$ is $1g$
Volume of $C{{O}_{2}}$ is $224ml$ which is equal to $0.224l$
The molar mass of $CaC{{O}_{3}}$is $100gmo{{l}^{-1}}$
Now we will apply mole concept to calculate the moles of $CaC{{O}_{3}}$
$n=\dfrac{W}{M}$  
Where, $n$ is the number of moles, $W$ is the weight of the compound and $M$ is the molar mass of the compound. 
Now, we will substitute the values in the above formula we get,
$n=\dfrac{1}{100}$
$n=0.01mol$
The moles of $CaC{{O}_{3}}$is $0.01mol$
Now, we will calculate the moles of $C{{O}_{2}}$
At STP,
$n=\dfrac{V}{22.4l}$
Now substituting the value of volume of $C{{O}_{2}}$ in litres we get,
$n=\dfrac{0.224}{22.4}$
$n=0.01mol$
The moles of $C{{O}_{2}}$is $0.01mol$
The thermal decomposition reaction of $CaC{{O}_{3}}$ is
$CaC{{O}_{3}}\to CaO+C{{O}_{2}}$
$0.01mol$ of $CaC{{O}_{3}}$will decompose to give $0.01mol$ of $CaO$ and $0.01mol$ of $C{{O}_{2}}$
The molar mass of $CaO$ is $56gmo{{l}^{-1}}$
On applying mole concept we get,
$n=\dfrac{W}{M}$
Where, $n$ is the number of moles, $W$ is the weight of the compound and $M$ is the molar mass of the compound. 
On substituting the values we get,
$0.01=\dfrac{W}{56}$
$W=0.56g$
Therefore, the mass of $CaO$ is $0.56g$

Hence, the correct option is A.

Note: Moles are defined as a scientific unit which is used to measure large quantities of atoms and molecules. It is defined as the amount of substance present in sample.
 $1mole=6.022\times {{10}^{23}}particles$
This is also called as Avogadro’s number $\left( {{N}_{A}} \right)$ .
-Molar mass is defined as the addition of atomic mass of atoms, combined in a molecule. Here, the molar mass of $CaC{{O}_{3}}$ is $100gmo{{l}^{-1}}$ .
-Moles are defined as the weight if the compound per molar mass of the compound.
-Formula mass is different from molecular mass. In formula mass, there is an addition of atomic masses of ion present in an ionic compound, whereas molecular mass is the addition of atomic masses of the atoms in a molecule