Question

Complete the following calculations.
-Calculate the mass of calcium that will contain the same number of atoms as are present in $3.2gm$ of sulphur.
[Atomic masses: $S = 32$ , $Ca = 40g/mol$ ]

Answer 1

Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance. One mole of substance contains $6.022 \times {10^{23}}$ which is equal to ${N_A}$ .

Complete step by step solution
Let us first read about the number of atoms and number of moles.
Atoms: It is the smallest unit of an element. The elements are made of the same kind of atoms. In the atoms there are three particles: electrons, protons and neutrons.
Electrons: They are the negatively charged particle having negligible mass. They move in the atoms outside the nucleus in a fixed orbit.
Protons: They are positively charged particles. They have mass. They are present in the nucleus (a special room in the atoms were neutrons and protons are present).
Neutrons: They have no charge but they have mass. They are also present in the nucleus along with protons.
Gram molecule: It is defined as the number of grams of the substance i.e. the molecular mass of the substance.
Atomic mass: It is defined as the total number of protons and neutrons present in the nucleus of an atom. It is represented by symbol A.
Atomic number: It is defined as the number of protons in the nucleus of an atom. It is represented by symbol Z.
Molecular weight of the substance: It is defined as the sum of the molecular masses of all elements present in the substance.
Number of moles: It is defined as the ratio of mass of the substance to the molecular mass of the substance.
And one mole of substance contains $6.022 \times {10^{23}}$ which is equal to ${N_A}$ . Now here we are given with $3.2gm$ of sulphur so the number of mole of sulphur will be $\dfrac{{3.2}}{{32}} = 0.1$ so the number of atoms in $0.1$ mole of sulphur will be $0.1{N_A}$ . And also in the question it is given that the number of atoms in the $3.2gm$ of sulphur and in a given mass of calcium are same and we have to find the mass of calcium. Now as the number of atoms in sulphur is $0.1{N_A}$ so the number of atoms of calcium will also be the same and hence the moles of calcium will be $0.1$ . And already we know the molar mass of calcium i.e. $40$ and let the mass of calcium will be $x$ . So the equation of number of moles of calcium will be
$\dfrac{x}{{40}} = 0.1 \\\ x = 4g \\\$

Note
Formula mass: It is defined as the sum of the atomic weights of all the atoms present in the compound. And if the compound is covalent in nature then the formula mass is known as molecular mass and if we are calculating mass of one mole of substance then it is known as molar mass.