Question

How many molecules are present in one gram of hydrogen?
A. 6.02 $\times$ 10$^{23}$
B. 3.01 $\times$ 10$^{23}$
C. 2.5 $\times$ 10$^{23}$
D. 1.5 $\times$ 10$^{23}$

Answer 1

Hint: Hydrogen is a diatomic molecule i.e. it is found in pairs. We know, two gram of hydrogen contains one mole of hydrogen. One mole is equal to Avogadro’s number. Now, the molecules present in one gram could be known.

Complete step by step answer:
a) Now, we know that hydrogen is a diatomic molecule with the atomic number 1, and atomic weight 1.

b) According to the basic mole concept, one mole of any atom is equal to the one gram of that element; but if we talk about the hydrogen in this case,
1 mole of hydrogen = 2 g of hydrogen, due to diatomic existence.

c) Now, we can say that one mole is equal to Avogadro’s no. i.e. 6.02 $\times$ 10$^{23}$ molecules. Thus, the first option is incorrect.

d) So, in 1 g of hydrogen it is Avogadro’s no. divided by 2,
i.e. $\dfrac{6.02 \times 10^{23}}{2}$ molecules = 3.01 $\times$ 10$^{23}$ molecules .

e) Thus, 3.01 $\times$ 10$^{23}$ molecules are present in one gram of hydrogen.

Therefore, the correct option is B.

Additional information: Avogadro’s number is the number of units in one mole of any substance, or its molecular weight in grams. It is the proportionality factor that relates the number of constituent particles in a sample with the amount of a substance in that sample.

Note: Don’t get confused between the statement that one mole of element is equal to one gram. It depends upon the existence, as we have already seen in the case of hydrogen. Suppose, we have to calculate for helium then we will consider one gram only, as helium is a monatomic molecule.