Question

Find how many moles of atoms are there in:
(A) $ 7g $ of Nitrogen.
(B) $ 4.6g $ of Sodium.
(C) $ 40g $ of Calcium.
(D) $ 14g $ of Lithium.
(E) $ 3.2g $ of Sulphur.

Answer 1

Hint: We know that the concept of general chemistry which deals with the chapter called as some basic concepts of chemistry, tells us about the mole, molecule and atoms and their masses along with it. This was initially not well known but later his works were known and later the Avogadro constant value was derived based on his law.

Complete answer:
First of all, let’s discuss the mole. Mole is that which tells us about the amount or the quantity of the substance. It can be in terms of either atoms, molecules, particles or grams, liters etc. Now considering the statement as; To calculate the number of moles of any substance, we should first know about the given mass and the molar mass of that very substance i.e., the atom or molecule and then, we can easily calculate the moles of that very atom or molecule. Mole of a substance describes the quantity of that very substance and if we know the mass and the molar mass of that very substance, then by using them we can easily calculate the number of moles of the substance.
According to the Avogadro law, mole concept, that is one mole of a substance is defined as the amount of a substance which contains as many elementary particles. Avogadro proposed a law which states that ‘equal volumes of different gases measured under the same conditions of temperature and pressure contain the same number of molecules.
Since we have $ 7g $ of Nitrogen and the Number of moles $ \dfrac{Given~Mass}{Atomic~Mass}=\dfrac{7}{14}=0.5~moles. $
Similarly, for $ 4.6g $ of Sodium thus, the Number of moles is $ \dfrac{Given~Mass}{Atomic~Mass}=\dfrac{4.6}{23}=0.2~moles. $
For $ 40g $ of Calcium thus, the Number of moles $ \dfrac{Given~Mass}{Atomic~Mass}=\dfrac{40}{40}=1~mole. $
For $ 14g $ of Lithium thus, the Number of moles $ \dfrac{Given~Mass}{Atomic~Mass}=\dfrac{14}{7}=2~moles. $
For $ 3.2g $ of Sulphur thus, the Number of moles $ \dfrac{Given~Mass}{Atomic~Mass}=\dfrac{3.2}{32}=0.1~moles. $

Note:
Remember that the Avogadro number also relates the molar volume of a substance to that of the average volume which is nominally occupied by one of its particles when both are expressed in the same units of volume.